Department of Biological Sciences, Macquarie University, New South Wales, Australia j o a n n a . b r z e s k a @ s t u d e n t s . m q . e d u . a u

Possibility of “urgency response” function in the terrestrial alarm call of noisyminers (Manorina melanocephala)Joanna Brzeska

Animal Behaviour 2014

Word count: 2075 (excluding abstract, figures, acknowledgements, tables and

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Noisy miners are a gregarious and highly vocal passerine, who frequently engage

in alarm calling and mobbing behaviour. This study focused on the possibility

of ‘urgency response’ functionality in the terrestrial alarm call of the bird.

The researcher hypothesized that noisy miners would denote ‘urgency response’

with an increased proximity of predator. The study found, however, that the

acoustic structure of the terrestrial alarm call (stimulated by human presence)

was not affected by closeness of potential predator. The researcher proposes

that a re-evaluation of the term ‘alarm call’ of noisy miners should be

undertaken. Further research of the “chur call” (Higgins et al. 2001) and its

social function, without giving it a functional label (as given by Jurisevic &

Sanderson 1994) should be undertaken in order to better understand the true

function of the vocalisations recorded during this study.

Keywords: noisy miners – alarm call – urgency response – terrestrial – function – social interactions – humans – habituation – chur call

The acoustic structure of alarm calls has been suggested to

denote two primary functions, termed: “functionally referential”

(i.e., predator type) and “urgency response” (Furrer & Manser

2009; Hollén 2009; Warkentin et al. 2001). The evolutionary

motive for “functionally referential” calls has been mostly

associated with the ability for animals to adapt appropriately to

different types of threats (Furrer & Manser 2009). “Functionally

referential” alarm calls can encode information of not only the

external environment, but also the internal state of arousal of

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the sender (Evans et al. 1993). Similarly, the “urgency response”

type alarm calls denote the level of urgency in both the external

environment (i.e. the proximity of the threat/predator), and the

internal state of the signaler. It has been found that animal

species throughout the world can use one type primarily, both

interchangeably, or even both alarm call types in a singular

alarm call (Manser et al. 2002).

The function of “urgency response” in an alarm call is vital

for antipredation as the change in acoustic structure helps

conspecifics apply better strategies in reaction to predation,

and therefore has Darwinian advantages in survivability. It has

been hypothesized that changes in peak frequency, fundamental

frequency, and syllable rate, are responsible for denoting degree

of urgency in an alarm call (Fichtel & Hammerschmidt 2002). For

example, California ground squirrels (Otospermophilus beecheyi) have

been found to increase the peak and fundamental frequency of

their alarm call with increased risk of predation. The same study

(Fichtel & Hammerschmidt 2002) found that yellow-bellied marmots

(Marmota flaviventris) increased syllable rate in their alarm call

with increased perceived threat.

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In terms of avian taxa, a study found that the white-browed

scrubwren (Sericornis frontalis) used “urgency response” in alarm

calling. The bird increased the peak frequency and syllable rate

of its “trill” with an increased proximity of a predator

(Leavesley & Magrath 2005). The higher peak frequency with closer

threat of predation was suggested to be directly correlated with

syllable rate. This reaction was found in the absence of any

other visual/auditory cues, indicating that it is primarily

associated with “urgency response”.

The noisy miner (Manorina melanocephala) is a highly gregarious

honeyeater (Meliphagidae) endemic to South-eastern and Eastern

Australia (Higgins et al. 2001). Noisy miners live mostly in

open-eucalypt forests (although they are becoming increasingly

urbanized [Ashley 2009]) in colonies that comprise of “coteries”

(consisting of 10-25 birds on average) and within these coteries,

“coalitions”, which usually comprise of 5-8 birds (Higgins et al.

2001). Although these units are mostly stable (coteries being the

most permanent), birds are known to move between units

interchangeably, however often this is not met without

competition of pre-established residents (Higgins et al. 2001).

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The noisy miner is known for its highly complex social structure

and cooperative behavior and the colony are often involved in

interspecific and intraspecific antagonistic interactions, and

commonly engage in “mobbing” of heterospecifics and conspecifics

alike (Kennedy et al. 2009).

Alarm calling among avian taxa, especially songbirds, is

usually broken up into two type categories: ‘terrestrial threats’

and ‘aerial threats’ (Wood et al. 2000). The “terrestrial alarm

call” of the noisy miner is mostly characterised by repetitive,

loud, broad-band and low frequency pulses. The primary energy in

the call is given to the first two or three harmonics, which

allows it to travel long distances (Kennedy et al. 2009). This

aids in the recruitment of conspecifics to the area (Jurisevic &

Sanderson 1994) in cases of mobbing and aggression toward

potentially threatening species. These alarm calls are primarily

referred to as “chur” calls (Higgins et al. 2001; Kennedy et al.

2009). The “chur” alarm call of noisy miners elicited by human

presence has been documented by Jurisevic & Sanderson (1994)

(Fig. 1) and is one of the main sources in scientific literature

for noisy miner alarm calls.

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Although it is known that noisy miners evoke functionally

referential alarm calls (i.e. distinct terrestrial and aerial

predator calls) (Jurisevic & Sanderson 1994), there has not been

any research (to the researchers knowledge) as to the “urgency

response” aspect of noisy miner alarm calling. In this study, the

researcher asks whether noisy miners evoke “urgency response” in

their terrestrial alarm calls elicited by human presence. It is

hypothesized that the noisy miner will change the acoustic

structure of its alarm call according to perceived predation

threat. It is predicted that the acoustic structure of the

terrestrial alarm call will increase in syllable rate with

increased perceived threat of predation. If the first hypothesis

is supported, the researcher also wants to investigate whether

the peak frequency and fundamental frequency of the acoustic

structure of the call will increase with perceived threat, and

whether this is directly correlated with increased syllable rate,

as found by Leavesley & Magrath (2005).

MethodsThe study was conducted for a period of 12 weeks from 24-3-

2014 to 8-6-2014 at Macquarie University, Sydney, Australia. The

sample size of noisy miners visibly present ranged from two to

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approximately 10. All subjects in the study were adults (no

juveniles were seen during the study period). To study potential

of predator proximity in urgency response calling, the birds were

recorded in three treatment groups, from three distances; termed

“far” (approximately 15m away), “close” (approximately 10m away)

and “very close” (approximately 2m away). These distances were

measured from the base of the tree in which the focal vocalizing

bird/s were perched. A small nondescript flag was planted in the

ground to indicate the correct distances for recording on

subsequent days. The calls were recorded for a period of 10

seconds(s) for each treatment group (far, close, and very close).

One recording from each distance, starting from farthest to

closest, was taken during each recording session (Fig. 2).

Recordings sessions were spaced with at least two hours between

each, to allow possible sensitization of birds to the predator

(myself). When the 10s recording sample did not contain the whole

of one element, the syllable was emitted from the total tally of

syllables in that sample. The recording session began as soon as

the researcher arrived at the first recording point (“far”), and

ended as soon as the last recording was finished (at “very

close”). The vocalisations of the birds were recorded using a

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Roland R-09HR and R-05 recorders and a Sennheiser MKE-600 shotgun

microphone. The calls were recorded at a 44.1KHz sampling rate

with 32-bit depth in an uncompressed .wav file and were later

analysed using Audacity 2.0.5 (Audacity 2013). The predator

stimulus walked toward the subjects during the recording sessions

in a non-threatening manner and did not vocalise or attempt to

provoke the birds in any way. The study was conducted under the

Macquarie University Research Authority 2013-23.

ResultsThe results of the study found there to be no statistically

significant variation in the overall acoustic structure of noisy

miner terrestrial alarm calling with changing distance of

potential predator. Although, on average, there was an increase

in average syllable rate and peak frequency when the potential

threat was closer (Table 1), this carries no statistical

credibility, and could be largely due to chance. Specifically,

the results pertaining to the syllable rate per 10s (Fig. 3)

showed no statistically significant variation (Kruskal-Wallis

test: H=3.11, df= 2, P>0.2[two-tailed]). The same test found no

statistically significant variance in the peak frequencies in the

three treatment groups (Fig. 4) (Kruskal-Wallis test: H=4.4,

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df=2, P>0.1[two-tailed]), and fundamental frequency across the

treatment groups (Fig. 5) (Kruskal-Wallis test: H=2.35, df=2,

P>0.3[two-tailed]).

The results also found little visibly direct correlation

between increased syllable rate and increased peak frequency over

the three treatment groups (Fig. 6). It also found little visibly

direct correlation in increased peak frequency with increased

fundamental frequency in the three treatment groups (Fig. 7).

These findings negate the suggestions of Leavesley & Magrath

(2005) that increased syllable rate is directly correlated with

peak and fundamental frequencies.

From the results and statistical analyses, it appears that noisy

miners do not use ‘urgency response’ as a function in their

terrestrial alarm calls.

DiscussionThe results found in this experiment suggest that there is

no correlation between proximity of a (human) predator and the

acoustic structure of the noisy miner terrestrial alarm call.

Therefore, it is reasonable to assume that the noisy miner does

not incorporate “urgency response” into its terrestrial alarm

call elicited by human presence. A possible reason for this

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finding may be noisy miner habituation to humans, as the bird

species has been found to increasingly inhabit densely human-

populated areas (Ashley 2009). A future study may perhaps

investigate whether these findings would correlate with a study

conducted of a population of noisy miners that have never been

exposed to human beings, or using a predatory stimulus that the

noisy miners have not been readily exposed to, and may therefore

require “urgency response” denotation.

As mentioned previously (see introduction), different animal

taxa may use only “functionally referential” calls or only “urgency

response” calls, or both interchangeably, or both in the same

alarm call (Manser et al. 2002). A study conducted by Furrer &

Manser (2009) suggested that avian taxa are more likely to use

“functionally referential” calls, rather than “urgency response”

calls, especially those that live in open vegetation (such as

noisy miners). Better visibility may result in favouring

“functionally referential” calls in denoting appropriate action

for predator type and “urgency response” being much less

necessary.

The results also found no correlation between increased

syllable rate and other acoustic elements of the alarm call (Fig.

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4 & Fig. 5). These results contradict the findings made by

Leavesley & Magrath (2005) regarding white-browed scrubwrens, who

showed a direct correlation in syllable rate, peak frequency and

fundamental frequency with increased proximity of predator.

Findings such as these have great implications for the dynamic

and diverse evolution and communication behaviour among avian

taxa, and the possible evolutionary/environmental reasons for

these differences (or similarities).

As noted previously (see introduction), it has been found

that the terrestrial alarm call of noisy miners is also used in

other contexts, such as mobbing and social facilitation.

Therefore, since noisy miners may be habituated to human

presence, the “alarm calls” may have been being used for

different reasons altogether during the recording period. The

researcher did in fact find (during own empirical observations)

that the birds were usually engaged in some form of intraspecific

communication or interaction. The author also notes that during

the recording period there were two sessions where the noisy

miners did not vocalise at all. This further supports the

implication that noisy miners were in fact not producing alarm

calls in response to predation stimuli, and may have been

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engaging in other interactions. There may therefore be a

necessity for the re-evaluation of the term ‘alarm call’ that has

been documented for noisy miners (Higgins et al. 2001; Jurisevic &

Sanderson 1994). It is not wholly clear whether the noisy miners

are emitting this vocalisation as an alarm call and it should

therefore not be labelled as such until extensive research and

studies have been conducted on the vocalisations of the songbird.

The researcher strongly recommends that future studies and

research do not give animal vocalisations functional labels, but

rather use labels of onomatopoeia-type, that do not assume or

infer social functions (such as “chur call”, as opposed to

“terrestrial alarm call”).

Future research on the functionality of the vocalisations

recorded in this study should perhaps focus on intraspecific and

interspecific interactions, and their relationship with these

‘alarm call’ vocalisations. As mentioned previously (see

introduction), the noisy miners are highly gregarious and ‘noisy’

animals, and thus their vocalisations should be studied with

social context and interaction at the forefront. The “chur call”

may have many different functions in different social contexts

and therefore requires much more research and analysis.

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ConclusionAs evidenced by this study, and past literature on

vocalizations of noisy miners, there is still great ambiguity in

the understanding of alarm calls, their purpose, and their

context. This study found that noisy miners seemed to be

unaffected by human presence, and that their alarm call may be

used in different contexts altogether in the presence of humans.

It also found there to be no direct correlation between acoustic

structures in alarm calls that were previously found to have

direct correlations (Leavesley and Magrath 2005). It is important

to conduct further studies on the acoustic structure of calls in

avian taxa, as this has implications for the understanding of

evolution of avian communication and behavior, and the

environmental and contextual reasons for these evolutionary

differences.

AcknowledgementsMy thanks to Tim Pearson and Dr. Jennifer A. Clarke for their

assistance in the logistics, research, data compilation and

analysis of this study.

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ReferencesAshley LC (2009) Does the presence of grevilleas and

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urgency-based changes in call structure. Ethology 108:763:777

Furrer RD & Manser MB (2009) The evolution of urgency-based

and functionally referential alarm calls in ground-dwelling

species. The American Naturalist 173:400-410

Higgins PJ, Peter JM, Steele WK (ed.) Handbook of Australian, New

Zealand and Antarctic Birds 5 (Oxford University Press 2001)

Hollén LI & Radford AN (2009) The development of alarm call

behavior in mammals and birds. Animal Behaviour 78:791-800

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Jurisevic MA & Sanderson KJ (1994) The vocal repertoires of

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Kennedy RAW, Evans CS, McDonald PG (2009) Individual

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Wood SR, Sanderson KJ, Evans CS (2000) Perception of

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Tables and Figures

Table 1: Mean value of each acoustic aspect in recording samples within each treatment group over the study period.

Figure 1. Spectrogram of the “terrestrial alarm call” of noisy miners elicited by human presence, as documented by Jurisevic & Sanderson (1994).

Mean values Far Close Very close

Syllable rate/10s 19 21 24

Peak frequency

(KHz) 3.9 4.1 4.2

Fundamental

frequency (KHz) 1.40 1.46 1.45

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Figure 2. Spectrograms samples (4s long) of recordings from each treatment group, chosen at random, displaying aesthetic features of the terrestrial alarm call elicited by human presence, as defined by Jurisevic & Sanderson (1994).

Figure 2 legend:a) spectrogram sample of “far” alarm callb) spectrogram sample of “close” alarm callc) spectrogram sample of “very close” alarm call

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Figure 3. Mean syllable rate per 10 seconds of “terrestrial alarmcall” of noisy miners under each treatment group (with standard deviation).

Figure 4. Mean peak frequency of “terrestrial alarm call” of noisy miners under each treatment group (with standard deviation).

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Figure 5. Mean fundamental frequency of “terrestrial alarm call” of noisy miners under each treatment group (with standard deviation).

Figure 6. Scatter plot displaying little visible correlation between increased syllable rate and peak frequency across all recording samples of “terrestrial alarm calls” of noisy miners elicited by human presence.

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peak

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Figure 7. Scatter plot displaying little visible correlation between increased peak frequency and fundamental frequency acrossall recording samples of “terrestrial alarm calls” of noisy miners elicited by human presence.

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