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Comparison of Hummingbird Time Budgets, Chase Frequencies, and Population Ratios in

a Mixed Species Tropical Environment:

Nathan M. Secrest

Guilford College: SIT Panama

Spring 2014, Panama.

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Table of Contents

Resumen Ejecutivo: ii:Abstract iii

Title Page 0:Introduction 1

:Methods 2Study ..........................................................................................................................................site 2

..................................................................................................................................Study subject 3- ..........................................................................................................Mist netting and Painting 3

...........................................................................................................................Artificial Flowers 6, :..............................................................................Feeding Chasing and Overall Behavior 8 .........................................................................................................................Territory Measure 10

.......................................................................................................................Studied Individuals 10 .................................................................................................................................Data Analysis 14

.................................................................................................................................Presentations 15

:Results 16- .....................................................................................................................................Mist netting 16

.......................................................................................................................Observational Data 17 .................................................................................................................................Time Budgets 18

............................................................................................................Individual Feeding Time 19 .........................................................................................................................Territorial Chases 21

.....................................................................................................................Chase Observations 23 ............................................................................................Feeding Times and Territoriality 24

:Discussion 25- ....................................................................................................................................Mist netting 25 ................................................................................................................................Time Budgets 26

........................................................................................................................Territorial Chases 28 .........................................................................................................Feeding and Territoriality 29

......................................................................................................................................Limitations 31

:Acknowledgments 32 :Works Cited 33

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Resumen Ejecutivo:

Mientras que hay más de 30 especies, han realizado pocos estudios sobre los presupuestos de

tiempo de colibríes tropicales. Esta información es útil porque podemos usarlo para ayudar a

educar a los lugareños sobre las diferencias interesantes de cada especie, así como ayuda en su

conservación proporcionando estimaciones de Cuántas flores uno podrían necesitar en su propia

casa para apoyar un colibrí de cada especie. Había dos partes con este estudio. Primero, En cinco

días usamos redes para atrapar los colibríes para obtener una estimación de población de la zona,

marcamos aves de principalmente dos especies diferentes que vivieron y protegieron territorios.

La segunda parte del estudio incluyó encontrando estos colibríes marcados en el campo y realizar

conducta sigue a través del día para explorar las diferencias entre alimentación y persiguiendo a

los comportamientos tanto entre especies e individuos de la misma especie. Los resultados de

ambos estos estudios mostraron que hubo casi el doble la cantidad de colibríes pechi-blanca

(Amazilia edward) que los colibríes cola-rufo (Amuziliu tzacatl) en el área. Ambas especies

perseguidos a los intrusos de su territorio sólo 2% de su tiempo total visitaron pero Rufous-colas

alimentan por casi el doble del tiempo (19%) en comparación con Snowy (10%). Otro hallazgo

sorprendente del estudio, demostrado que los casos de persecución se duplicaban con creces en

frecuencia entre las horas de 8 y 10 en comparación con otros momentos del día. Este estudio

puede actuar como base para futuras investigaciones en esta área y con estas especies tropicales

colibrí. También este estudio puede ser utilizado para crear una mejor conciencia de comunidad

de estas especies que son importantes para la polinización.

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Abstract:

While there are over 30 species, few studies have been done on the time budgets of tropical

hummingbirds. This information is useful because we can use it to help educate locals on the

interesting differences of each species and provide estimates of how many flowers one might

need on their own property to support one hummingbird of each species. There were two parts to

this study. First, five days of mist-netting took place to gain a population estimate of the area and

mark birds of primarily two different species that lived and held territories in the area. The

second part of the study involved finding marked hummingbirds in the field. Once found,

behavioral follows of individuals and neighboring individuals were performed through out the

day to explore the differences between feeding and chasing behaviors both between species and

individuals within the same species. The results of both studies showed that there were almost

double the amount of Snowy-bellied Hummingbirds (Amazilia edward) than Rufous-tailed

Hummingbirds (Amuziliu tzacatl) in the area. Both species chased off intruders from their

territories for only about 2% of their total time viewed but Rufous-tails fed for almost double the

time (19%) compared to Snowy's (10%). Another surprising find of the study showed that chase

instances more than doubled in frequency between the hours of 8 and 10am compared to other

times of day.

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Introduction :

Hummingbirds are some of the smallest and fastest flying birds in world. They have evolved to

have very small agile bodies with wings that can beat between 12 and 90 times per second

(Hummingbird 2014). This rapid movement results in a very high energy cost of feeding that has driven

these birds to find concentrated high energy food sources. Nectar from flowers provides a very high

sugar content that is energetically easy to digest.

In ecological studies, time and energy budgets are essential to better understand the division of

self-maintenance and reproductive activities of a population (Wolf and Hainsworth 1971). If we know

more about time budgets of a species, future studies could compare their results as a way of

understanding a populations change over time and overall health and food availability of the species.

In terms of conservation of species and habitats this type of work is essential. Behavioral

follow studies, provide a mountain of information on behaviors like feeding, resting and protecting

territory. Hummingbirds in particular have been shown to be very practical for these types of studies

because they have small territory sizes and periods of docile activity, making them easy to keep in sight

for long periods of time (Pearson 1954). Previously, most studies that have been done on hummingbird

feeding budgets and territoriality (Wolf and Hainsworth 1971, Paton and Carpenter 1984, Hixon 1983,

Powers and Mckee 1994) were done in the United States. Few studies have been done on tropical

hummingbird time and energy budgets (Boyden 1978, Dearborn 1998), thus limiting the variety of

hummingbirds studied.

To my knowledge there has never been a study comparing the feeding, chase and resting time

budgets of two different species living in the same site. The reasons for attempting such a study are

simply to develop a baseline data for this mixed species population and to see the differences in

foraging behavior between two populations. This study done in Loma Bonita, Panama attempts to

answer the following questions:

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• Is there a difference between feeding time, chase time and resting time of different species

of hummingbirds who live intermixed feeding on one specific food source?

• What are the population ratios species in the area?

Knowledge about the population of hummingbirds and their feeding behaviors is essential

for the conservation of these species because we can use this information to help protect the

habitat of these birds. If we know how much they eat and how frequently, we can also use this

information to educate locals about how many flowers they need to have in their own yard to

support the diet of one hummingbird. Additionally, with this baseline information on the species'

feeding behaviors other studies could look at other groups and compare their results to get a

better idea of population health or annual feeding cycles of these hummingbirds.

It was hypothesized that bigger of the two species studied would spend more time feeding

to maintain their bigger body size and less overall time chasing because they could more

effectively chase and threaten others with their big body. This study also helped in answering

secondary questions like “why was it observed that the smaller of the two species held all of the

most flower dense territories?” and “was there a specific time of day that feeding or chases

increased dramatically?”

Methods :

Study Site:

The area observed during the duration of this study was a hilly area located both in and

just outside of an overgrown plot of land that was used as horse grazing territory. A total of 5

species of hummingbirds were observed to be there at one point during the study period.

Within the study site, there was a main patch of densely packed flowers. There was

another section to one side that had a semi-dense area of the same flower. Much of the area

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above this was overgrown with grasses and thorny plants but had many areas with the same

flowering plant that had grown taller than the dense or semi-dense flowering areas (Figure 1).

This pattern of scattered plants strewn about the hillside went as far as the eye could see upwards

and held many territories of hummingbirds that were hard if not Impossible to get to.

Study Subjects:

Of all the five species observed in this area, 3 of these were common occurrences during

the time of the study. Two of these three, the Rufous-tailed Hummingbird (Amazilia tzacatl) and

the Snowy-bellied Hummingbird (Amazilia edward), held territories within the study site while

the other species, Garden Emerald (Chlorostilbon Assimilis) did not and instead frequently visited

many territories in the hopes of stealing some nectar. The two territory holding species were the

focus of the feeding behavior study.

Mist-netting and Painting:

Two mist nets were set up for 4 hour sessions once a day (6:00am-10am) for either one or

two days per location depending on the success of the first mist-netting day (Figure 1). My

assistant and local, Luis Carmen Rodriguez, helped me in setting up, tying, opening and closing

the mist nets daily using the MoSI protocol (Desante and Saracco 2009-10).

The wind played a big factor in helping hummingbirds escape from the mist nets once

they flew in and were initially trapped. Almost half of the hummingbirds that flew into these nets

escaped within seconds after being trapped because they were able to struggle through the fine

netting material with a little help from the wind to widen the holes. Because these birds do not

weigh more than about four grams the wind was easily enough to help them escape before we

were able to get to the net.

For this reason, during the five mist-netting days, most our time was spent sitting very

close to each net so that we could react as quickly as possible to any hummingbirds that would

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fly in. This method also allowed us to free the hummingbirds as quickly as possible so as not to

harm or stress them any more than needed. Once a bird was caught, I would go quickly over to

the net and untangle the bird usually starting with its feet but at times starting with the head

because the head would hit the net first and drop down getting tangled with its beak. Using the

bird bander's grip (index and middle finger in a V around the neck with the bottom of the V on

the shoulders and back of the bird), the bird was worked up. First, the bird was identified by

species. Afterward we took the wing, tail and beak length as well as looked for things like age

(Juvenile or Adult) sex, and molt. After this, the hummingbird was painted with non-toxic

washable paint. Each hummingbird received a different color (black, white, red, yellow, green,

blue, teal, or purple). The first birds caught were painted on their breasts and bellies because of

the distinguishing white belly that many of them had. When all easily visible colors had taken for

birds of a single species, subjects were painted on their backs or mantle so as to distinguish

between birds of the same species if spotted again in the field (Figure 2)

This painting of birds was done in hopes of being able to refind and track most of the

hummingbirds in the area after we had netted them. After painting and recording the color of

each bird we then released the bird back into the wild. In the latter days of bird banding we were

able to watch where the released bird flew and could sometimes track it back to its home territory

which it usually went to quite quickly after being released. This was not the case for the first two

days of banding because we were fairly busy with the next bird and frankly didn't think to watch

where it would return to.

During the entirety of the mist-netting procedure, safety of the hummingbirds was a high

priority. Birds on average were released within 5 minutes after being captured. Care was taken

to not harm the wings of the birds. If a hummingbird looked to be getting stressed the bird would

be given some nectar through the nostrils using capillary tubes.

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Data were recorded for this section of the experiment and used to help identify specific

individuals within the hummingbird community for further study.

Figure 1: A map of the area studied which includes the locations of all the mist-nets used as well

as information about which days each net was used (D1 Day-1) during the 5 day mist-netting

period. A rough sketch of the territories studied in relation to the nets can be seen as well as the

areas cut before the study (cut sections) and the areas cut before the burnings during the study

below. S indicates a Snowy-bellied Hummingbird (A. edward) individual while R represents a

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Rufous-tailed Hummingbird (A. tzacatl).

Figure 2: Picture A (Left) Snowy-bellied #1 painted Violet on its chest. Picture B (right) Snowy-

bellied #10 Green Back.

Artificial Flowers:

The cognition portion of the study attempted to replicate a study done called “Timing in

Free-Living Rufus Hummingbirds” by Henderson and Hurly (2006)

During the bird banding days artificial flowers were made in an attempt to imitate the

target flower shape and color (Figure 3) and placed in the center marked bird's territories. .

This first step of the process was intended to get the birds accustomed to feeding from

these artificial flowers when available. Unfortunately, during these days of attempting to get

individuals to eat from artificial flowers, there were only two instances where I believe these

flowers were used by the hummingbirds and I was not there to witness either of them. I can

merely speculate that this was hummingbirds because when I returned after an afternoon in the

city, I found a few of the flowers empty and had been drained of nectar. However, when I

replaced the artificial flowers in the territories and watched (Figure 3).

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After two days of trying to get these birds to feed from artificial flowers, I realized my

time constraints and continued with my back-up plan that I had started while waiting for these

birds to feed.

In other experiments, done very similarly to mine they had little trouble getting wild

hummingbirds to feed on their artificial flowers. This discrepancy in time taken to train birds to

use feeders could be because many of the birds studied in the US have lots of contact with

hummingbird feeders along their migration path where as these hummingbirds, who only locally

migrate, live in an area where hummingbird feeders are not a part of daily life here so these birds

have probably never seen an artificial flower in their lifetime which perhaps explains their initial

reaction to these artificial flowers.

Figure 3: Picture A (left): An example of the flower trying to be imitated by our artificial

flowers. Picture B (right): Artificial flowers placed on the transplanted flower plant with the

flowers having been removed and replaced with our artificial ones.

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Feeding, Chasing and Overall Behavior:

With my remaining time in Loma Bonita, I decided to follow through with my secondary

plan of taking behavioral follows of 30 minutes in order to better understand the inner workings

of territoriality, feeding behaviors, chasing behaviors, and how different individuals within a

population can be.

Behavioral Follows were done between April 17th and April 28th. During this time 8

individual hummingbirds of two different species were followed for a total of 3 hours (6

behavioral follows of 30 minutes) each. Four Snowy-bellied Hummingbirds (A. edward) were

chosen based on paint markings and neighboring territories to these painted individuals.

Likewise, the four Rufous-tailed Hummingbirds (A. tzacatl) chosen were also for coloration

reasons and because they neighbored territories of painted individuals.

In total 4 of the 8 individuals chosen for the behavioral follows were painted individuals

(2 Rufus-tailed and two Snowy-bellied) while the other four neighbored three of the painted

individuals territories. This choice to study neighboring territories was to gain a better insight

into how neighbors interacted as well as how these territories were kept (ie were they rigid and

inflexible? Or did they fluctuate depending on the day?). In addition to these reasons, studying

birds in nearby territories aided the research process because I did not have to spend lots of time

traveling between sites in order to track another individual. Because of this, I was able to get up

to 5 behavioral follows done in one morning session of three hours between the hours of 7 and

10am. Neighboring individuals were easliy recognized by their perching behavior. Each

individual had spots that they really liked to perch within their territory. Additionally, when

feeding these birds would not be chased by another individual when inside their territory. Thus,

by returning everyday I could tell if there was a shift in territories or if another individual had

taken over that territory because they acted differently within it.

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During the initial planning stages of this part of the project, and ethogram was created

including the following behaviors: Feed (FE), Move Perch (MP), Rest/Sit (RE), Chase (Ch), Get

Chased (G Ch), Preen (Pre). Leave Territory (Le). Not Visible (NV), Return (Ret), Vocalize (VO),

Squeak (SQ) [for Snowy-bellied Hummingbirds (A. edward) only], Chip (warning and regular),

Poop, and Stolen From (STF).

A stopwatch was used with pencil and paper to conduct the behavioral follow study. As

soon as the hummingbird started an action (leaving the perch usually) the lap function on the

stopwatch was pressed while maintaining visual of the bird so as to know what action was being

performed and where I could expect this individual to be in the next few seconds if I looked

down at the watch and paper quickly and back up. Feeding time in particular was thus slightly

elongated by this procedure because I included all time spent flying to and from the flowers.

There were times when so much was happening at once that I could not keep track of all

actions or missed writing down when an individual rested after chasing an individual. In that

case, when calculating the time spent feeding or chasing I used a set time of 4 seconds per chase

on average and 4 seconds for feeding. The feeding time was decided upon after observationally

seeing that it took about 4 seconds to feed on one flower and likewise the average time of chase

took about 4 seconds but could range from 1-15 seconds depending on how far they chased the

intruder.

Overall, there were definitely some actions missed due to the difficulty of terrain, size of

the territory, and personal distractions like locals wanting to know how my project was going.

While the work I was doing was important it was not worth ignoring a culture that thrived on

daily small talk and conversation. One of the points of my project here was to open the

communities eyes to more of the world of science so ignoring them and being rude for simply

one data sheet was highly counter productive.

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Territory Measure:

After just one or two behavioral follows, it was quite obvious where the boundaries of

each territory were. One could tell because each individual would have a point at which they

tended to rest at the edge of its territory or almost right in the middle where it could view all parts

of its territory. This observation in addition to chases of intruders when they entered into another

hummingbird's territory helped me in estimating the boundaries of each territory.

Territories were measured with a 30 meter tape measure. Since many of the territories

were oddly shaped I measured a square or sometimes a trapezoid encompassing all flowers

utilized in their territory.

Studied Individuals:

For each individual studied, a letter and Number were assigned based on the first letter of

their common name and the number in which they were added to the study (ie Snowy-bellied,

second added =S2). Pictures of each territory are shown below (Figure 4). A map of each where

each territory was located in relation to one another is shown above (Figure 1).

Snowy-bellied Hummingbird (A. edward) #1 S1:

This hummingbird lived on a territory that was 14.5m by 13m with a square of 6m by 4m

that had its flowers cut. In total the area of territory was measured to be 164.5m^2. When netted,

it was painted teal on its belly and released. His/Her territory bordered the bigger patch of

flowers where S3 lived and also shared territory lines with R1 and S4. During the behavioral

study period the lower part of its territory that stretched across the dirt road was cut when the

field below it was burned in preparation for the growing season. After this day, this hummingbird

abandoned its territory and was not seen from that day on. For this individual I was only able to

obtain 3 total behavioral follows.

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Snowy-bellied Hummingbird (A. edward) #2 S2:

This hummingbird's territory was discovered when watching R#2 during the first days.

During the course of this study, I was intrigued by this birds interactions with its neighbors (R1,

R2 and R3). At the beginning of the study it held a territory that was only 11m by 4m but by the

end of the study it held a territory of 25m by 11m. Thus increasing its territory from 44m^2 to

275m^2 in about 10 days. This increase of territory size added more than tripled the number of

flowers it protected. This process was aided by one of the neighboring birds abandoning its

territory but this process was incredibly interesting to watch as changes to territories were made

almost daily.

Snowy-bellied Hummingbird (A. edward) #3 S3:

This hummingbird lived in the most flower dense area in my study site. It held a territory of

8.5m by 6m which totaled 51m^2. When netted, this bird was painted white on its back and

slightly on its wings. When captured for a second time, yellow was added to its head to

differentiate from another of the same species that had accidentally been also painted white on its

wings and tail. During the course of the study this individual was generally in its territory but at

the very end of the project it was unable to be located and its territory seemed to be mostly empty

only being used by other neighbors to feed from occasionally. This disappearance coincided with

the first rains received in Loma Bonita for the start of the rainy season.

Snowy-bellied Hummingbird (A. edward) #4 S4:

This hummingbird was chosen because it was neighbors with S3, S1, R1 and R2. This

hummingbird held a territory that was not nearly as dense with flowers in comparison to

territories of S3 or S1. This bird was very cooperative during my study allowing me to sit very

close in the center of its territory without getting scared and moving away from me.

Rufous-tailed Hummingbird (A. tzacatl) #1 R1:

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This hummingbird was chosen because it was a neighbor of the teal painted S1. This bird shared

territory boundaries with S1, S2, S4, R2 and slightly with R3. Half of the behavioral follows

were performed before S1 abandoned its territory and half were performed after this event

occurred. When S1 abandoned its territory the territory of R1 expanded from 14m by 18m

previous to 28m by 18m . The area of this territory started at 252m^2 and increased to 504m^2 .

Behavioral follows after the change in territory size will be marked in the results.

Rufous-tailed Hummingbird (A. tzacatl) #2 R2:

This hummingbird was chosen because it was one of the first rufus individuals that we could

locate its territory relatively easily. When netted this bird was painted white on its breast. This

bird held a territory of 15m by 31m which totaled to 465m^2 and was neighbored territories with

S4, S2, R1 and slightly with R3. This bird was the first to have a behavioral follow performed

and was initially chosen to be part of the artificial flower study but was not able to be trained to

use artificial flowers consistently in the amount of time available for my study.

Rufous-tailed Hummingbird (A. tzacatl) #3 R3:

This hummingbird was chosen because it held similar size territories compared to other

individuals around the area. It also neighbored the territories of S2, R2 and part of R1's territory.

This bird unfortunately disappeared around the same time as S1 but since I had started taking

data on this bird later than S1, it had the least number of behavioral follows performed before it

disappeared for good. Before it left, it held a territory that was 21m by 11m which totaled to

231m^2 with some of that being relatively dense flowers and other parts with much more sparse

and younger flowering plants. Only one Behavioral follow was done for this bird.

Rufous-tailed Hummingbird (A. tzacatl) #4 R4:

This hummingbird was chosen because it was another painted individual that we were able to

locate and measure its territory fairly accurately. This individual had many neighbors but none

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that participated in this particular investigation. This individual held the most sparse territories of

all the individuals studied which also caused it to be one of the hardest birds to follow accurately.

Because the territory was located on very rough, hilly and overgrown terrain most of the territory

size had to be estimated rather than measured with a measuring tape. Additionally, behavioral

follows taken on this individual were performed in a tree to maintain as much visual contact with

the bird as possible.

During the study, on Tuesday April 22nd the bottom section of farm land was burned which

meant that they cut many of the flowers on the downhill side of the road. Directly after this

habitat destruction, S#1 and R#3 left the study site and have not been seen since. Those two and

S#3, who left 2 or so days after were not followed for the full 6 sessions of 30 minutes each. The

data taken after this event on some of the other individuals was kept together for overall feeding

comparisons but separated to indicate change in feeding time after territory shift.

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Figure 4: Shown are the territories of the individuals studied. In order from left to right: (Top

row) Territories of S1 and R1 (later all taken by R1), S2 and R3 (S2 later took if over), R4.

(bottom row) S3, R2 and part of S2 below, and S4.

Data Analysis:

Mist netting data were compiled and used to estimate the total population of different

species of hummingbirds as well as the species abundance in the area. This information along

with some observational data were used in conjunction with some of the behavioral follows data

to answer the question of why only one species held the territories with the most dense flower

concentration.

We hoped that the Mark and Recapture method could be used for this study to estimate

population size but given the destruction of much of the surrounding environment during the

behavioral section of the study, population estimate would have been skewed because for this

equation it is assumed that no changes to the population were made (ie migration from site)

which is observationally untrue.

Feeding behavior data were taken from the behavioral follows and compiled into total

seconds spent feeding (FE). After this, time not visible (NV) was calculated and subtracted from

the total seconds in 30 minutes (1,800). Percent time spent feeding was then calculated by the

formula:

FE (s)/[1800-NV]

Percent time feeding was calculated among an entire species as well as individually to see

if there was a difference in feeding budgets inter-specially as well as intra-specially.

In addition to feeding time, chase time and number were calculated to understand when

most of the territory chases occurred.

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Presentations:

As a finale to my project and a way to give back to the community for all the support they

have given me, I had planned to give a total of 5 presentations of various lengths. The purpose of

these presentations was to communicate with the community the reason why I thought it

necessary to come back to Loma Bonita to study hummingbirds and to potentially enlighten

people to the interesting world of birds. Four of my presentations were planned for the Schools

in both Loma Bonita, and El Cope.

Each presentation started with showing the students how to open the mist-nets as well as

explaining how they are used in scientific studies. During the course of the presentation, the nets

are left open so that when we returned we hopefully had caught a bird or two to show how this

form of research worked. After the nets were opened, an introduction to my topic including a few

vocabulary words was given. After this, I showed a video of my project and explained what I did

during my research process. Directly after this, I presented my results and talked about the

significance of research projects like this. What else can we learn and question now that we

know this information? What types of implications does this project show us about the

conservation of these animals?

After the presentation in Loma Bonita, contact info was exchanged with some teachers to

give them a contact of some ornithologists and project ideas of things they could do in their

classroom involving birds as a science project. The nets were closed and taken down.

Unfortunately, the El Cope School district told us we had a presentation on a day when

there was no school nationwide, so Connor and my presentations for that school were not able to

happen. In total only two presentations of 5 were done , but both in Loma Bonita were a success.

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Results :

Mist-netting:

In a total of five days we captured and marked 17 hummingbirds of 3 different species

(Table 1). After painting and releasing the birds we sighted 6 of the 17 in the area around our

site. Four of those sighted birds were included in the behavioral study because they were sighted

early on in the process and lived in the nearby territories that were easily studied.

Of all birds captured, 11 of the 17 were Snowy-bellied Hummingbirds (A. edward), 5

were Rufous-tailed Hummingbirds (A. tzacatl) and one was a Sapphire-throated Hummingbird

(Lepidopyga Coeruleogularis). The average wing length of the Snowy-bellied Hummingbirds

(A. edward) caught was 52 cm while the average wing length of Rufous-tailed Hummingbirds (A.

tzacatl) was 58. The average tail length of the Snowy-bellied Hummingbirds (A. edward) was

28.7cm while the Rufus-tailed tail length averaged to 31cm. Average beak length of Snowy's was

18cm with the Rufus' being 21cm (Table 1)

Every bird except for two were recorded as molting during the time they were captured.

Overall, Rufous-tailed Hummingbirds (A. tzacatl) were the biggest species found in that area with

the Saphire-throated being one of the smallest.

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Table 1: Shows all birds caught and measured in the 5 day mist-netting portion of the study. The

right most column illustrates what color each one was painted for individual identification in the

second part of the study.

Observational Data:

Many Garden Emerald Hummingbirds (C. Assimilis) were observed close and at times in

the net for no more than 1 or 2 seconds but none were able to be recorded. Many times these

smart hummingbirds would fly right up to the net and then move underneath or over it. There

were a few observed times of the Garden Emeralds (C. Assimilis) using the net to their advantage

because they knew that the territory holder was scared and would not chase them close to the net.

They would thus eat the nectar of the flowers closest to the net and not be chased often or if they

Hummingbird species Wings Tail Beak Paint Color/location

04/13/14 Snowy-Bellied #1 52 27 20.4 Violet Chest04/13/14 Snowy-Bellied #2 50 28 21.5 Yellow Chest04/14/14 Snowy-Bellied #3 50 27 20.4 Green Chest04/14/14 Snowy-Bellied #4 47 29.5 20.7 Black Chest04/14/14 Snowy-Bellied #5 54 29 19.3 Teal Chest04/16/14 Snowy-Bellied #6 54 27 18.3 White Back Yellow H 04/17/14 Snowy-Bellied #7 54 30 18.6 White Back +Tail04/17/14 Snowy-Bellied #8 52 30 1.87 Red Back04/17/14 Snowy-Bellied #9 54 29 19 Yellow Back04/17/14 Snowy-Bellied #10 53 29 18.6 Green Back04/17/14 Snowy-Bellied #11 53 30 18.9 Blue Chest

Averages Snowy-Bellied 52.090909091 28.681818182 17.960909091

04/13/14 Rufus Tailed #1 58 N/a 18.9 Blue Chest04/14/14 Rufus Tailed #2 54 29 20 Red Chest04/14/14 Rufus Tailed #3 57 28 21.6 White Chest04/15/14 Rufus Tailed #4 60 30 20.5 Yellow Tail04/16/14 Rufus Tailed #5 61 33 24 Blue Back

Average Rufus Tailed 58 30 21

04/14/13 49 31 14 White ChestRecaptures:

04/13/14 Snowy-Bellied Violet Chest04/15/14 Snowy-Bellied Teal Chest04/15/14 Rufus Tailed White Chest

Sapphire-Throated #1

Secrest 18

were they would simply dart out of the way and watch the chaser get caught in the net.

Another observation was made that most birds trapped in the net seemed to be ones who

came from other territories trying to steal some nectar from the most dense areas of flowers. This

observation came from the fact that we were not able to locate hardly any of the painted birds in

the area we were studying yet we painted over 17. It was later observed that we were able to

locate very few these flower patches way up at the top of the hill as well as to the left and right.

It was also observed that many birds flew far downhill after they were liberated from being

measured.

Of the 17 captured birds only 2 held a section of the territory where the nets were placed.

These two that were trapped had flowers within their territory on both sides of the net.

Time Budgets:

After over 1000 minutes of observation in total, the percent time spent feeding for each

species was quite different. The Snowy-bellied Hummingbirds (A. edward) fed for an 10.01%,

chased others for 2.35%, and rested for the rest (87.64%) of the time visible in their territory. The

Rufous-tailed Hummingbirds (A. tzacatl) fed for 19.14%, chased for 2.00% and rested for

78.87% while in their own territory (Figure 5). Both species were observed being chased from

other territories but that time accounted for less than .01% of total time observed. There were a

few instances where Garden Emerald Hummingbirds (C. Assimilis) were able to be followed for a

some time. While they were only followed for a total of about 30 minutes the difference in

feeding time is drastic. Within those 30 minutes they were observed to be feeding for 69.7% of

the time. The behavioral follows for the Garden Emeralds (C. Assimilis) were not done within

their territory because they did not seem to hold territories where my study took place.

Secrest 19

Figure 5: Shown is the % feeding time of three species observed at the site. The Rufus and the

Snowy were watched for over 500 minutes while the Garden Emerald (C. Assimilis) was

watched for only 30 because it was quite difficult to follow because it did not hold any set

territory where it could be found often. A Ttest- of the seconds spent feeding between behavioral

follows of Snowy-bellied Hummingbirds (A. edward) and of Rufous-tailed Hummingbirds (A.

tzacatl) proved to be significant (P<.0005).

Feeding time of Individuals:

When analyzing individual feeding times of individuals within the same species one can

see that the percentages are fairly similar between species given that there were not more than 6

behavioral follows done on any one individual. R4 had the lowest percent time spent feeding

among Rufous-tailed Hummingbirds (A. tzacatl) while S3 had the highest percent time feeding

within its species (Figure 6).

Snowy-Bellied Rufus-Tail Garden Emerald0

10

20

30

40

50

60

70

Percent Time Feeding

In Total Time Observed

Species

% F

eedi

ng T

ime

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Figure 6: Shown are the individual % time spent feeding over the course of the study to see if

there is a difference between individuals within a species. *Represents insufficient data which

could easily skew results.

Overall, the feeding time budgets in relation to time of day were showed that there did not

seem to be a significant difference between time spent feeding in the morning compared to the

afternoon. There did seem to be a spike of feeding at 8am (Figure 7).

S1 S2 S3 S4 R1 R2 R3* R40

5

10

15

20

25

30

Percent Time Spent Feeding

Individuals

Individuals

% T

ime

Spe

nt F

eedi

ng

Secrest 21

Figure 7: Shown here are the combined time budgets of both species to show the overall time

spent feeding at different hours of the day. Feeding times between the afternoon and morning

were not significantly different (P>.1).

Territorial Chases:

The number of chases an individual protecting a territory had during one behavioral

follow ranged from 0-21. Many times the same intruder was chased multiple times because after

every chase it would continue to re-enter the territory and attempt to feed on the same flowers.

This behavior was especially relevant when talking about Garden Emeralds (C. Assimilis)

entering other territories because instead of running they would generally duck out of the way

and continue trying to feed instead of being chased completely off the territory.

When looking over the data, there was a large spike in territoriality chases between the

times of 8am and 10am compared to other times of the day (Figure 8) . During these times there

were up to 21 chases recorded in one 30 minute follow. The most number of chases recorded at

other times of the day was eleven but the second highest was eight. The average number of

07:00 AM 08:00 AM 09:00 AM 03:00 PM 04:00 PM 05:00 PM0

246

810

1214

1618

Feed % in Accordance with Hour of the Day

Time of Day

% F

eedi

ng T

ime

Secrest 22

chases during the hours of 8am and 9am behavioral follows was more than double that of the

average number of chases recorded at any other time during the study (Figure 9).

Data for R4 was left out of this analysis for two reasons. First, given the difficult terrain

of R4's territory it was hard to accurately record Chases and instances of having nectar be stolen

because at no point could I see the entire territory very well. Secondly. Observations were made

that most of the chases occurred in flower dense areas or nearest to the main patch of flowers.

Hummingbirds coming in search of food seemed to come to these areas and then be chased into

neighboring territories right outside the most dense patch of flowers. Because R4's territory was

so far from the main patch, we decided to exclude that data from the number of chases.

One behavioral follow which started at 7:45am and was thus placed in the 7am category,

also depicted this interesting trend. During the first 15 minutes of the behavioral follow only 1

chase was recorded but after that first 15 minutes 8 chases were recorded from that individual at

spaced out times within those 15 minutes.

07:00 AM 08:00 AM 09:00 AM 03:00 PM 04:00 PM 05:00 PM0

2

4

6

8

10

12

Average Number of Chasesvs Time of Day

Time of Day

# of

Cha

ses

Secrest 23

Figure 8: Shown here is the average number of Chases performed by an individual in a 30

minute Behavioral Follow in accordance to the time of day.

Figure 9: Shown here is the average number of chase occurrences in relation to the time of day.

There are significantly more chases by an individual during the hours of 8 and 9 am than there

are during all other times of day that Behavioral follows were taken of the day (P value =.00014).

Chase Observations:

During the study, I witnessed countless chases between hummingbirds. One observation that

stuck out between species is that I noticed Snowy-bellied Hummingbirds (A. edward) chasing off

Garden Emeralds (C. Assimilis) and other intruders in areas that were not in their territory

boundaries. This was especially true in the most dense patch of flowers. All the territories held

in that dense patch of flowers were held by Snowy-bellied Hummingbirds (A. edward).

There were many intrusions by the Garden Emeralds (C. Assimilis) that caused these

Snowy-bellied Hummingbirds (A. edward) to chase them up to five or six times in a minute

because they would run at them at full speed and all the Garden Emeralds (C. Assimilis) had to do

was duck out of the way and continue to feed. The only species that I saw actually hit another

8 and 9am All Other times (7am 3,4,5pm)0

2

4

6

8

10

12

Comparison of Number of Chases based on Time of Day

Time of Day

Avg

# of

Cha

ses

Secrest 24

hummingbird during a chase was the Rufous-tailed Hummingbird (A. tzacatl). At times the

would drive the other hummingbird (usually Garden Emerald (C. Assimilis)) into the ground after

hitting them and continue to chase them more effectively it seemed than the Snowy-bellied

Hummingbirds (A. edward).

Feeding times and Territoriality:

As previously mentioned, three of the subjects left before all of their behavioral follows

could be completed. As a result of territory abandonment the neighboring territory holders

shifted their territories to include much of this new available territory into their habitat. Three of

the other individuals (S2, S4 and R1) had about equal numbers of behavioral follows done before

the territory shift and after. The results show that two of the three increased their % time feeding

while one had a slight decrease (Figure 9).

Figure 9: Shown is the % time spent feeding before a territory expansion and after a territory had

been expanded. Individuals R1 and S4 increased their % time feeding while S2 slightly

decreased its feeding time. R1 and S2 data proved to be not signifcant using Ttests (p>.1) while

S4 data proved significant (p<.05).

R1 Before R1 After S2 Before S2 After S4 Before S4 After0

5

10

15

20

25

Change in Time Spent Feeding Before and After Territory Size Increase

Individuals Before/After

% T

ime

Spe

nt F

eedi

ng

Secrest 25

Discussion :

Mist-netting:

After catching and painting 17 individuals, the number of unpainted individuals visible

was still quite large in the main area of the study site. From this observational data and from the

data of marked hummingbirds, I would guess there to be between 30-40 individual hummingbirds

that visit that site daily including the ones that hold territory on that area.

Because of the change in the site during the project, mark and recapture couldn't be

accurately done. For population ratios we found that there was slightly greater than a 2:1 ratio of

Snowy-bellied Hummingbirds (A. edward) to Rufous-tailed Hummingbirds (A. tzacatl)

The data from mist-netting doesn't seem to fully represent the percentage of all species

that inhabit the study site. As previously mentioned, in observations Green Emerald

hummingbirds were never trapped in the net long enough to measure them, hence the data from

mist-netting shows that there are only 3 species in the area when observations tell us that there

are up to 5 species that inhabit that one study site. The fifth species observed was the Stripe-

throated Hermit (Phaethornis striigularis) and was only seen occasionally at the end of the study

period.

What the data from the mist-netting does show us is that overall Rufous-tailed

Hummingbirds (A. tzacatl) are bigger in size in almost every way (wings, tail, and beak). This

information brings up the question of “If the Rufous-tailed Hummingbirds (A. tzacatl) are bigger

why don't they hold the most flower dense territories?”.

Another question that came from this data is: why were so many of the individuals marked not

able to be located afterward? Since many of the painted individuals from the first day were

observed almost two weeks later still containing much of the paint markings its not likely that

other birds were able to wash off the paint. Instead it seems more likely that the netted

Secrest 26

individuals were ones who came from farther territories looking to steal from this flower dense

area and instead ran into the net because they did not have time to observe and learn from other

individuals before being trapped. This also would explain why so many individuals who

protected territories near the net were not netted. They were able to watch and learn from

intruders how dangerous these nets were so they were able to avoid them after witnessing them

blowing in the wind.

One of the challenges during these mist-netting days was the windy conditions that came

with the territory. The site was located on a mountain hillside which entailed a lot of wind that

would start between 8 and 9 am and last consistently throughout the day. One of the reasons for

starting so early on mist-netting days was to avoid as much wind as possible because when wind

catches the nets, they don't function as well as they were meant to.

This escaping of individuals could have directly contributed to the number of individuals

not painted in the territories they held. Its very possible some of the many that escaped were

territory holders right next to the net locations but after being able to escape once they were not

able to be fooled twice or were already practiced at escaping the net and knew that if they

struggled in the net when wind blew they could usually get free.

Time Budgets:

The most interesting result of this experiment was perhaps the percent fed difference

encountered between the Rufous-tailed Hummingbird (A. tzacatl) species and the Snowy-bellied

Hummingbird (A. edward) species. This difference of amounts to almost 10% in total time

allocated for feeding. This could be for many reasons but I believe its most likely to be that

Rufous-tailed Hummingbirds (A. tzacatl) are bigger and therefore need to eat more to sustain

their body size. This difference could also be explained by a greater feeding efficacy of Snowy-

bellied Hummingbirds (A. edward) requiring less time to feed on their flowers within their

Secrest 27

territory.

The feeding times of the Rufous-tailed Hummingbirds (A. tzacatl) match well with other

studies that have analyzed feeding budgets of other hummingbird species like Rufus

hummingbirds (Hixon 1983; Stiles 1971; Wolf and Hainsworth 1971). However, the time

budgets for Snowy-bellied hummingbirds which is at the low end of the spectrum among

hummingbirds in % time spent feeding ( Wolf and Hainsworth 1971). This % is lower than other

papers recorded feeding times of hummingbirds more recently (Powers 1988).

With this data we can conclude, that Rufous-tailed Hummingbirds (A. tzacatl) feed for

significantly more time than Snowy-bellied Hummingbirds (A. edward). We don't have sufficient

information to conclude that Garden Emerald Hummingbirds (C. Assimilis) eat more than other

species but it would be an interesting question to follow up on to see if hummingbirds who don't

hold territories eat for significantly more time than hummingbirds that hold territories. This

seems to be the case and my hypothesis would be that they use different approaches to feeding.

The ones who hold territory know and remember which flowers have recently been feed on so

they can feed more efficiently while others who don't hold that territory seem to enter and try to

feed from every flower because they don't have knowledge of which flowers have been fed from

recently and which ones don’t. Therefore, there is a higher chance that by feeding from just one

flower they wouldn't receive any nectar.

Observationally, these non-territory holders seem much smaller which would help them

sustain flight for longer time without using as much energy so that when they do find flowers

with nectar that energy will go farther than it would in a bigger heavier hummingbird. This

observation matches other studies that state smaller hummingbirds have the highest mass-specific

metabolic rate among hummingbirds (Suarez 1992).

While this metabolic rate information explains the actions of the smallest hummingbirds

Secrest 28

in the territory, it seems to contradict the finding that Rufous-tailed hummingbirds (A. tzacatl) eat

more feed for almost double the time as Snowy-bellied hummingbirds (A. edward). This then

prompts the question: what causes this stark difference in feeding times? Some possibilities

could be foraging efficiency rates like intelligence levels and ability to remember which flowers

have been visited most recently, or even just patience levels.

Territorial Chases:

Another interesting find of the study was this huge spike in territoriality chases that

started around 8 in the morning and subsided around 9:30 or 10am. Statistically, these findings

proved to be very significant showing that there must be something about this time that causes

more intruders to come into nectar dense territories looking to steal. This observation seems to

coincide with my observations that hummingbirds will wait to feed from a specific flower for

about an hour. If daily activity starts around 6:30 or so, then after an hour the hummingbirds can

feed from their territory and then would have time to go searching for extra food because their

territory would have been cleared of nectar and wouldn't need to be protected for about 10-20

minutes because no hummingbird would have success even if they tried to feed there.

One likely explanation, revolves more around the flower itself. In other similar studies done

about bird territoriality, they found that nectar production in climates similar to this is at its

highest point around mid-morning meaning (Gill 1975). This increase in food availability could

draw other hummingbirds to the area knowing they can probably steal a bit of the excess. This

explanation is aided by the information in Figure 7 as well that shows a slight peak in feeding at

8am.

Another possible explanation for this behavior could be that the main stealer of nectar, the

Garden Emeralds (C. Assimilis), finished up their daily cycle of other flowers in other areas and

had a routine of arriving to this area around 8 or 9 in the morning where they would then be

Secrest 29

chased between territories of neighboring individuals thus increasing the overall number of

chases for this area studied at this time. More information on the behavior of, the Garden

Emeralds (C. Assimilis) would be required to know this for sure but the nectar production peak

could also drive this behavior from all species of hummingibrds looking for food. For future

studies if these hummingbirds were able to be netted, it would be interesting to place a GPS

tracker on these individuals to see how far they move in a day and to find out if they have any

specific territory that they rest at or protect. It would also be interesting to see if insect activity

on the flowers also increased during these hours of the morning.

On another note, chases of neighbors and intruders of other species was recorded

frequently. There were few instances where intruders were able to steal from a territory without

being chased. Many of these times occurred when the owner of the territory had left for a short

time. This information indicates that at this time period food was restricted because all intruders

were chased off a high percentage of the time (Powers and Mckee 1994). Additionally, it was

observed that Snowy-bellied Hummingbirds (A. edward) of neighboring territories often chased

smaller intruders like the Garden Emerald (C. Assimilis) and then would feed on the territory

directly after chasing away an intruder. This observation helps answer the question of why

Snowy's held the territories with the most flower density if they were the smaller of the two most

prevalent species.

Feeding and Territoriality:

While the data shows that two individuals increased their feeding time after a territory

increase, it is difficult to conclude anything from this section of the data because many factors

could have affected the data other than just territory increase. The drying of the flowers over the

course of the study could have caused more overall feeding time to get the same amount of nectar

because there weren't as many flowers on each stem. Additionally, since this was not the main

Secrest 30

question of the study, there is not sufficient data to conclude anything about changes in feeding

behavior with territoriality increase. Oddly enough, this increase in feeding time contradicted the

findings of a similar study done which concluded that increased territoriality resulted in an

overall decrease in feeding time (Hixon 1983). While no flower density manipulations were done

here, this fact could be explained by hypothesizing that previously their foraging time was

insufficient to their consumption needs which caused an increase in feeding when there was more

opportunity to do so. This data could also reflect the seasonality of these flowers and agree with

Hixon's study which stated that as food availability decreased (the flowers dried out and closed

leaving less flower density) foraging time increased (Hixon 1983).

Originally, it was planned to see if there was a correlation between flower density with in

a territory and feeding time. However, due to many of the subjects abandoning their territory

causing neighboring subjects to modify their territory boundaries it was difficult to do any sort of

analysis on territory area and feeding time because the territories of these individuals were in a

time of transition as this study was taking place. Thus, even though data was collected on

territory size estimates and number of flowers within the territory no thorough analysis was done

on this subject because it was sometimes unclear what the territory boundaries were on a daily

basis as they expanded.

Figure 9 is a good example of the difficulties of doing such a correlation between territory

size and feeding times. For this data it was decided that the start of the territory increase occurred

directly after the territory abandonment of S1 and R3. This division put about half of the

behavioral follows for those three individuals on either side of that diversionary line. However, it

is difficult to conclude anything from this data because of the lack of behavioral follows at

similar times of day as well as the lack of knowledge of when the territorial lines began to

change. Observationally, it seemed that the R1's territory increased in size almost every time I

Secrest 31

visited for a behavioral follow but S2's territory had a big jump one day and then seemed to

shrink the next day with the pressures of R2 trying to take some of S2's original territory. At

minimum this data opens up more questions as to how territory shifts occur within species mixed

populations as time goes on. It could be that many of my behavioral follows captured an interim

period where territories were being re-established for the beginning of the rainy

season. New flowers were opening up in other locations creating more draw and potentially less

competition for food which could have caused those who abandoned their territory leave in the

first place.

Limitations:

Data analysis time was a major limitation of this study. When reading other papers that

included formulas for feeding time budgets and territoriality in relation to nectar availability and

feeding times, I found that I wished I had the time to plug some of my data into those formulas

but because I had so much data from all my behavioral follows it would have taken me hours and

hours to plug in all my data pertaining to longest feeding bouts or percentages. Instead, for time

reasons it was more efficient to simply calculate time and instances spent chasing and feeding for

each behavioral follow.

This limitation also coincided with the lack of electricity and internet that I was faced with

during my study. While I truly learned a great deal more from my experience by not being

distracted by technology during my experiment, this fact prohibited me from inputting my data

into an excel spreadsheet little by little, as I would have liked to do, as opposed to all at once

during a period of less than a week.

Due to the lack of a statistical program and time for analysis, ANOVA's for feeding,

chasing and resting were not performed.

Like many researchers, I wish I had more time to collect and analyze data from this

Secrest 32

project because as more time passed I had more and more questions that I wished to answer

about this mixed species population of hummingbirds.

Acknowledgments:

This project could not have been accomplished without the help from key individuals.

Much thanks goes to SIT-Panama especially Ruben Gonzales and Chelina Batista for their

advice throughout the process. A special thanks goes to Chelina and her friend Betsy for taking

time out of their busy lives to drive me to Loma Bonita and help me get started on the mist-

netting portion of my project, as well as giving me advice on how best to proceed with my project

involving artificial flowers and other obstacles I may encounter during the process.

Another huge thanks must also go to my Host Family Carmen and Angela in Loma Bonita.

Without Carmen's help this project could not have happened the way it did. His attention

to detail, reliability, and knowledge of the area were just some of the invaluable characteristics he

contributed to the project that allowed me to be as successful as I was. Both Angela and Carmen

were extremely supportive in this process taking valuable time out of their days to help make my

project the best it could be.

As for my project, a big thanks goes to the owner of the land Lila, who allowed me to set

up mist-nets and to conduct much of my study on her wonderful property. With that, I must also

thank the hummingbirds for being fairly cooperative when being painted and for enduring my

presence which allowed me to study them from very close without having a big impact on their

natural lives.

I'd like to thank the people of Loma Bonita for accepting me into their small town and

being truly interested in what my project was about. Thank you to both schools in Loma Bonita

and El Cope for allowing me to share my passion and project with their classes and a special

thanks goes to Yariza Jimenez for organizing and sending me SIT's projector for the

presentations.

Finally, I'd like to thank everyone in the semester like Ruben, Connor, and friends in the US for

supporting me during this period of intense work and at times intense isolation.

Secrest 33

Works Cited:

Boyden, Thomas C. "Territorial Defense against Hummingbirds and Insects by Tropical

Hummingbirds." The Condor 80.2 (1978): 216-21. JSTOR. Web. 04 May 2014.

<http://www.jstor.org/stable/10.2307/1367921?ref=search-

gateway:ce6bb822d38e109998f097eb9eb75c69>.

Dearbor, Donald C. "Interspecific Territoriality by a Rufous-Tailed Hummingbird (Amazilia

Tzacatl): Effects of Intruder Size and Resource Value." Biotropica 30.2 (1998): 306-13.

JSTOR. Web. 04 May 2014. <http://www.jstor.org/stable/10.2307/2389172?ref=search-

gateway:2e1d781cf264e15eba04614b5d0601aa>.

Gill, Frank B., and Larry L. Wolf. "Economics of Feeding Territoriality in the Golden-Winged

Sunbird." Ecology 56.2 (1975): 333. Print.

Henderson, Jonathan, T. Andrew Hurly, Melissa Bateson, and Susan D. Healy. "Timing in Free-

Living Rufous Hummingbirds, Selasphorus Rufus." Current Biology 16.5 (2006): 512-15.

Print.

Hixon, Mark A., F. Lynn Carpenter, and David C. Paton. "Territory Area, Flower Density, and

Time Budgeting in Hummingbirds: An Experimental and Theoretical Analysis." The

American Naturalist 122.3 (1983): 366. Print.

"Hummingbird." Amazing Facts about Hummingbirds | OneKind. N.p., n.d. Web. 27 Apr. 2014.

Paton, David C., and F. Lynn Carpenter. "Peripheral Foraging by Territorial Rufous

Hummingbirds: Defense by Exploitation." Ecology 65.6 (1984): 1808. Print.

Pearson, Oliver P. "The Daily Energy Requirements of a Wild Anna Hummingbird." The Condor

56.6 (1954): 317-22. Print.

Powers, Donald R., and Todd Mckee. "The Effect of Food Availability on Time and Energy

Expenditures of Territorial and Non-Territorial Hummingbirds." The Condor 96.4 (1994):

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1064-075. Print.

Powers, Donald R. "Field Metabolic Rate and Food Consumption by Free-Living Anna's

Hummingbirds (Calypte Anna)." Physiological Zoology 61.6 (1988): 500-06. JSTOR.

Web. 03 May 2014. <http://www.jstor.org/stable/10.2307/30156158?ref=search-

gateway:741ea0a9afe53e471071e48390065dcd>.

Suarez, R. K. "Hummingbird Flight: Sustaining the Highest Mass-specific Metabolic Rates

among Vertebrates." Experientia 48.6 (1992): 565-70. Print.

Wolf, Larry L., and F. Reed Hainsworth. "Time and Energy Budgets of Territorial Hummingbirds." Ecology 52.6 (1971): 980. Print.