ORIGINAL PAPER

Fledging success of little auks in the high Arctic: do provisioningrates and the quality of foraging grounds matter?

Johanna E. H. Hovinen • Katarzyna Wojczulanis-Jakubas •

Dariusz Jakubas • Haakon Hop • Jørgen Berge •

Dorota Kidawa • Nina J. Karnovsky • Harald Steen

Received: 20 April 2013 / Revised: 3 February 2014 / Accepted: 4 February 2014

� Springer-Verlag Berlin Heidelberg 2014

Abstract Long-lived birds often face a dilemma between

self-maintenance and reproduction. In order to maximize

fitness, some seabird parents alternate short trips to collect

food for offspring with long trips for self-feeding (bimodal

foraging strategy). In this study, we examined whether

temporal and spatial variation in the quality of foraging

grounds affect provisioning and fledging success of a long-

lived, bimodal forager, the little auk (Alle alle), the most

abundant seabird species in the Arctic ecosystem. We

predicted that an increase in sea surface temperature (SST),

with an associated decrease in the preferred Arctic zoo-

plankton prey, would increase foraging trip durations,

decrease chick provisioning rates and decrease chick

fledging success. Chick provisioning and survival were

observed during three consecutive years (2008–2010) at

two colonies with variable foraging conditions in Spits-

bergen: Isfjorden and Magdalenefjorden. We found that a

change in SST (range 1.6–5.4 �C) did not influence trip

durations or provisioning rates. SST was, however,

negatively correlated with the number of prey items

delivered to a chick. Furthermore, provisioning rates did

not influence chick’s probability to fledge; instead, SST

was also negatively correlated with fledging probability.

This was likely related to the prey availability and quality

in the little auk’s foraging grounds. Our findings suggest

that predicted warmer climate in the Arctic will negatively

influence the ability of parents to provide their chicks, and

consequently, the fledging prospects of little auk chicks.

Keywords Bimodal foraging � Fledging success �Alle alle � Calanus � Svalbard

Introduction

Under stressful conditions, for example when there is a

food shortage, long-lived species are predicted to prioritize

self-maintenance, and thus survival, at the cost of current

reproduction (Stearns 1989; Zera and Harshman 2001).

Seabirds are typically long-lived species (Lack 1968).

Their breeding efforts require a lot of energy since they

need to regularly return to a nest site to feed offspring

(Ricklefs 1983). In order to maximize the energy delivered

to offspring, and also maintain their own body condition

efficiently, some seabirds have adopted a bimodal foraging

strategy of interspersed short and long foraging trips

(Weimerskirch et al. 1994; Ropert-Coudert et al. 2004;

Congdon et al. 2005; Welcker et al. 2012). Parents self-

feed and store energy during long trips (LTs), and subse-

quently spend this energy gathering food for their chicks

during short trips (STs) (Grandeiro et al. 1998; We-

imerskirch et al. 2003; Brown et al. 2012; Welcker et al.

2012). If there is not sufficient amount of food close to

breeding sites or if food availability or quality deteriorates,

J. E. H. Hovinen (&) � H. Hop � H. Steen

Norwegian Polar Institute, Fram Centre, Tromsø, Norway

e-mail: johanna.hovinen@npolar.no

J. E. H. Hovinen

University Centre in Svalbard, Longyearbyen, Norway

K. Wojczulanis-Jakubas � D. Jakubas � D. Kidawa

Department of Vertebrate Ecology and Zoology, University of

Gdansk, Gdansk, Poland

J. Berge

Faculty of Biosciences, Fisheries and Economics, UiT-The

Arctic University of Norway, Tromsø, Norway

N. J. Karnovsky

Department of Biology, Pomona College, Claremont, CA, USA

123

Polar Biol

DOI 10.1007/s00300-014-1466-1

bimodal foragers may commute longer distances and/or

spend more time on foraging (Duriez et al. 2000). This may

reduce the chick provisioning rate (e.g. Duriez et al. 2000;

Davoren and Montevecchi 2003) and hence decrease the

amount of prey and energy delivered to chicks, and nega-

tively influence survival of chicks (Schaffner 1990).

The bimodal foraging strategy has been documented in a

number of procellariiform seabird species (Chaurand and

Weimerskirch 1994; Weimerskirch et al. 2001), and

recently also in the little auk (Alle alle), a small (*160 g),

long-lived, zooplanktivorous alcid (Steen et al. 2007;

Welcker et al. 2009a, b, 2012; Wojczulanis-Jakubas et al.

2010; Brown et al. 2012). The little auk is probably the

most abundant seabird species breeding in the high Arctic

(Stempniewicz 2001; Barrett et al. 2006). It is a monoga-

mous colonial breeder, which lays a single-egg clutch in

rocky crevices in talus slopes, incubates an egg for

*29 days and provisions the hatched chick until it fledges

*20–31 days later (Stempniewicz 1981; Harding et al.

2004; Wojczulanis-Jakubas and Jakubas 2012). Both sexes

incubate the egg and feed the chick, but prior to fledging

only males are left to take care of the chick (Harding et al.

2004; Wojczulanis-Jakubas and Jakubas 2012). Each par-

ent alternates LTs interspersed with 3–5 STs daily to pro-

vide adequate energy for themselves and for the chick

during the intensive and short summer breeding period

(Steen et al. 2007; Welcker et al. 2009a, b; Wojczulanis-

Jakubas et al. 2010; Welcker et al. 2012). The main prey of

little auks during summer is lipid-rich Calanus copepods

that account for up to 90 % of their diet (Karnovsky et al.

2003; Kwasniewski et al. 2010). Little auks are major

harvesters of these copepods, and thus have an important

role in the nutrient cycling of the Arctic marine ecosystem

(Barrett et al. 2006). Arctic, cold water associated Calanus

glacialis and Calanus hyperboreus contain *25 % more

lipid (mg-1 dry weight) than the smaller, Atlantic (boreal)

counterpart Calanus finmarchicus, and are thus the most

preferred calanoid copepod prey by the little auks (Wes-

lawski et al. 1999; Scott et al. 2000; Karnovsky et al. 2003;

Jakubas et al. 2007, 2011). The quality of the little auk’s

foraging ground is largely influenced by the distribution of

warm Atlantic (T [ 3 �C, salinity [ 34.9 PSU) and cold

Arctic (T \ 0 �C, salinity: 34.3–34.8 PSU) water masses

(Saloranta and Svendsen 2001) that regulate the distribu-

tion and abundance of these three Calanus species (Willis

et al. 2006; Daase and Eiane 2007; Blachowiak-Samolyk

et al. 2008; Stempniewicz et al. 2013).

In the present study, we investigated the bimodal for-

aging strategy of parent little auks and the fledging success

of their chicks at the west coast of Spitsbergen, Svalbard.

Inter-annual variation in the inflow and temperature of

Atlantic water into this area can be high (Walczowski et al.

2012), and some of the previous little auk studies have

suggested that resulting changes in the abundance of

associated zooplankton prey may lead to substantial vari-

ation in the little auk foraging effort (Karnovsky et al.

2003; Jakubas et al. 2007, 2011; Kwasniewski et al. 2010).

Increase in the amount of Atlantic zooplankton relative to

Arctic zooplankton may force little auks to spend more

time in search of their preferred Arctic prey (Jakubas et al.

2007, 2011; Kwasniewski et al. 2010; Gremillet et al.

2012). Consequently, little auks may increase the duration

of their LTs and decrease provisioning rates of their chicks

(Welcker et al. 2009a) that in turn could result in lower

amount of food and energy received by the chicks (Ricklefs

1983). This may cause decreased chick survival and

fledging success (Welcker et al. 2009b).

We wanted to further investigate the above-mentioned

suggestions and thereby (1) to test whether varying

oceanographic conditions with their associated zooplank-

ton prey affect foraging trip durations (we considered both

STs and LTs) and chick provisioning rates of little auks,

and then (2) to examine whether variations in these

oceanographic conditions, foraging trips and provisioning

rates influence fledging success of little auk chicks. We

assessed the differences in oceanographic conditions with

ocean surface temperature (SST)—SST has been shown to

be strongly linked to species composition of local zoo-

plankton communities in our study area, with large, lipid-

rich copepods inhabiting cold water (Karnovsky et al.

2010). We predicted that long-lived auks with low fecun-

dity prioritize self-maintenance over that of their chicks,

and that (1) LT durations are longer when SST is higher;

(2) chick provisioning rates are lower when SST is higher;

(3) fledging success of chicks is lower when LT durations

are longer and provisioning rates lower.

Materials and methods

Study area

We collected data during the chick rearing phase (July–

August) in three consecutive years (2008–2010) at two

colonies in the Svalbard archipelago: Isfjorden (78�120N,

15�200E) and Magdalenefjorden (79�350N, 11�050E)

(Fig. 1). Both fjords as well as the adjacent shelf sea area

outside the fjords are regularly supplied with both Atlantic

water from the West Spitsbergen Current and Arctic water

from the South Cape Current (Nilsen et al. 2008, Kwas-

niewski et al. 2010; Trudnowska et al. 2012; Jakubas et al.

2013). Furthermore, the nearby marginal ice zone at the

north-west off Spitsbergen (Fig. 1) provides a good quality

foraging ground for little auks breeding in Magdalenef-

jorden (Kwasniewski et al. 2010; Jakubas et al. 2011, 2012,

2013).

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123

We used SST (�C) to characterize oceanographic con-

ditions and the quality of little auk’s foraging ground. We

estimated mean SST for the chick rearing period (July) of

each study year for an area of *5,500 km2 adjacent to

each of the two colonies (Fig. 1). These areas were chosen

such that they covered the maximum foraging ranges of

little auks observed in our study area (*150 km; Jakubas

et al. 2013). We acquired monthly means of SST data at

4 km 9 4 km horizontal resolution from the moderate-

resolution imaging spectroradiometer (MODIS/aqua;

http://disc.sci.gsfc.nasa.gov/giovanni) and computed the

final July means by averaging all monthly data points

available within the selected areas mentioned above.

Foraging trip duration and chick feeding rate

We estimated foraging trip durations and chick feeding

rates by observing marked adults at both colonies. Birds

were caught during late incubation or early chick rearing

period with a mist net or noose carpet, and marked with a

stainless steel ring and a unique combination of three

plastic colour rings. The observation area at both colonies

was chosen such that it ensured the presence of sufficient

number of birds with visible nest entrances as well as

minimized disturbance.

We carried out observations non-stop for 48 h, from 15

to 26 July in Isfjorden and 27 July to 3 August in Mag-

dalenefjorden, when the chicks were 8–17 days old

(Table 1). During 48-h watches, two observers registered

time of departure and arrival of all the marked birds in the

observation areas. Only birds that returned to colony with

food for their chick (noticeable by their bulging gular

pouch below the beak) were registered. We defined for-

aging trip duration as the time between departing the col-

ony with an empty gular pouch and returning to the colony

with a filled gular pouch. We logged a feeding event when

a bird left the nest with an empty gular pouch after entering

it with a full gular pouch. During the study, we monitored a

total of 114 birds at the two colonies (Table 1).

Chick food samples

We collected 8, 27 and 15 gular pouch samples in Isfjor-

den, and 18, 59 and 30 samples in Magdalenefjorden (in

2008, 2009 and 2010, respectively). Data on the diets from

Magdalenefjorden are also presented in Jakubas et al.

(2011) and Kidawa et al. (submitted). We caught birds

during the 2nd and 3rd week of chick rearing with a mist

net or noose carpet, and procured samples by gently

scooping out the content from the gular pouch. We sam-

pled each bird only once in order to avoid malnutrition of

their chick and a pseudoreplication problem. Samples were

transferred to 4 % formaldehyde solution in the field. Prior

to identification of prey species, samples were rinsed with

fresh water and all big prey items ([ 1 cm) were picked up

and identified. The rest of gular pouch samples were split

(with a simple box splitter; Motoda 1985) into subsamples

that contained approximately 150–300 individuals of Cal-

anus spp. The copepodite stage of Calanus spp. was

determined, and prosome length (PL, mm) measured from

the tip of the cephalosome to the distal lateral end of the

last thoracic segment (Hirche et al. 1994). Identification of

the species was based on the stage and PL (Weydmann and

Kwasniewski 2008). The remaining prey items in subs-

amples were also calculated and identified to species or

taxon. Total number of prey in a gular pouch was extrap-

olated from the subsample.

Chick fledging success

To estimate fledging success of the chicks, we monitored

nests at both colonies. Nests containing egg were located

and marked during late incubation. They were monitored

Fig. 1 Little auk colonies (black dots) in Isfjorden and Magdalenef-

jorden, main water currents transporting Atlantic water (West

Spitsbergen Current) and Arctic water (South Cape Current), average

location of the marginal ice zone at the northwest off Spitsbergen

during the study period, and areas (squares; *5,500 km2 adjacent to

each of the colonies) for which sea surface temperature (SST �C) was

extracted

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every 2–3 days during the hatching period in order to

detect hatch date. During the chick rearing period, nests

were monitored every 4–5 days in order to record chick

survival. Frequency of nest checks was increased to every

2–3 days when chicks started to fledge. The presence of an

egg or a chick in the nest was confirmed with a use of light-

scopes (Moritex Europe Ltd, Cambridge, UK) or flash-

lights. We considered chick fledged if it disappeared from

the nest at the age of C20 days post-hatching (Harding

et al. 2004; Wojczulanis-Jakubas and Jakubas 2012).

During the study, we monitored a total of 321 chicks at the

two colonies (Table 1). Due to problems with capturing

sufficient number of birds from particular nests, the chicks

monitored and parents registered during the trip observa-

tions were from different family units.

Statistical analyses

To classify single trips as either ST or LT, we determined

an unbiased data-driven cut-off value separately for each

colony and year according to the procedure by Welcker

et al. (2009a). The bimodal distribution of foraging trip

durations of the little auk can be considered as two separate

log-normal distributions of STs and LTs. The cut-off value

was determined as the minimum sum of variances of both

trip types given their log-normal distributions. Derived cut-

off values varied slightly between the two study sites and

years (Isfjorden: 5–6 h, Magdalenefjorden: 6–8 h). We

calculated daily chick feeding rate as the number of times a

foraging bird returned to the colony and entered the nest

with a filled gular pouch within the 48-h period, divided by

two. The number of prey items delivered to a chick by one

parent during a day was estimated by multiplying the

average number of prey items in one food load (i.e. gular

pouch) with the daily chick feeding rate.

To examine inter-annual and inter-colony variation in

SST data (including all monthly data points available), we

applied an analysis of variance (ANOVA) with study year

and colony as explanatory variables. In all the other models

(see below), we assessed the potential effect of SST on trip

durations, chick provisioning rates and chick fledging

success by first including only year and colony as

explanatory variables into models. Then, we ran additional

models where the year effect was replaced with SST. We

also assessed the effect of other potential explanatory

variables by replacing the year effect with them.

Foraging trip durations between the years and colonies

were compared by fitting linear mixed effects (LMEs)

models with colony and year as fixed effects, and separate

models were run for STs and LTs. Additional LMEs for

both trip types were run to test whether SST, chick age

(day) and LT duration (in ST model) influence trip dura-

tions. Since trip durations and chick ages were estimated

from different parents and nests, respectively, we used a

mean chick age for each colony and for each year (all nests

combined; Table 1). Due to repeated trip duration esti-

mates of the same individuals, ‘‘individual’’ was included

as a random effect into all of these LME models.

We compared daily chick feeding rates between the

years and colonies by applying generalized linear mixed

effect (GLME) model with Poisson error distribution and

with ‘‘individual’’ as a random effect. We fitted additional

GLMEs to test whether SST, LT and ST durations, or chick

age influence daily feeding rates.

We used logistic regression (LR) with binomial error

distribution to test for difference in fledging success

between the years and colonies. Fledging success was

expressed as 0 if the chick survived \20 days (unfledged

chick) and 1 if the chick disappeared from the nest

C20 days post-hatching (fledged chick). We ran additional

and separate LRs to test the effect of SST, LT and ST

durations, and daily chick feeding rates on fledging suc-

cess. In addition, we fitted generalized linear models

(GLM) with Poisson error distribution to test whether

colony and year, or SST and daily chick feeding rates

influence chick’s fledging age. Mean values of each of

these explanatory variables for each year and colony were

used due to lack of real parent–chick pairs.

We log transformed data when needed to meet the

assumption of normality. All results are reported as mean

values with associated standard errors. We performed

model selection by using the Akaike information criterion

adjusted for small sample size (AICc). We excluded all

models with DAICc [ 2 as they have very limited support

Table 1 Mean hatching date

and number of hatched chicks,

and number of parent birds

observed and age of the chicks

(day) during 48-h non-stop

observations (dates shown) in

Isfjorden (I) and

Magdalenefjorden (M)

Year Colony Hatching date Chicks 48-h watch Adults Chick age (day)

2008 I 9 July 21 24–26 July 11 15.8 ± 0.7

M 16 July 47 29–31 July 24 13.0 ± 0.5

2009 I 12 July 22 26–28 July 6 14.9 ± 0.4

M 19 July 77 27–29 July 32 8.0 ± 0.4

2010 I 6 July 39 15–17 July 9 9.7 ± 0.5

M 16 July 115 1–3 August 32 17.0 ± 0.4

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(Burnham and Anderson 2002). We report all selected

models with their AICc weights and evidence ratios. AICc

weight is the likelihood of the model given the data and the

set of candidate models. Evidence ratio is the relative

weight of the model against the best model. Statistical

analyses were performed in R 2.15.0 (R Development Core

Team 2012).

Results

Sea surface temperature, chick age and trip duration

Model selection suggested that oceanographic conditions

and thereby the quality of little auk’s foraging ground

differed between the two colonies, and varied throughout

the study period (Table 2); SST was higher in the Isfjorden

area (range 4.70–5.38 �C) than in the Magdalenefjorden

area (range 1.59–2.36 �C), indicating a higher presence of

Atlantic water masses in the former compared to the latter

area (Fig. 2a). Top selected LME models describing ST

duration included an interaction between colony and chick

age or SST (both models had similar support; Table 2).

These interactions were, however, ambiguous, because

generally ST duration was similar (*2.2 h) at both colo-

nies, regardless of the differences in chick age or SST

(Fig. 2b). Only exception was 1 year in Isfjorden when STs

were on average shorter (1.7 ± 0.2 h; Fig. 2b). Top

selected LME model describing LT duration included only

the year effect (Table 2): LT duration was shortest during

2009 (Isfjorden: 12.5 ± 1.6 h, Magdalenefjorden:

11.8 ± 0.5 h) and longer (up to 16 h) during 2008 and

2010 at both colonies (Fig. 2c). Neither SST nor chick age

influenced LT duration as models including these effects

were not among the selected models (Table 2).

Daily chick feeding rate

There was strong evidence from model selection that only

LT duration controlled the daily chick feeding rate

(Table 2), with decreased number of food loads delivered

to a chick when LT duration increased (Fig. 3). Feeding

rate was similar at both colonies (range 4.1–4.8 food loads

chick-1 days-1; Fig. 3). Basically no support was shown

for the influence of ST duration on daily feeding rates

(Table 2). Also, intra-annual differences in feeding rate

between the two colonies, and effect of SST and chick age

on feeding rates, were not supported by model selection—

as GLME models including these effects were not among

the selected models (Table 2).

Food delivered to a chick

The average number of prey items delivered to a chick by

one parent during a day was lower in Isfjorden (\6,300)

than in Magdalenefjorden ([7,400) throughout the study

Table 2 Model selection results for the models used in the statistical analyses

Model Response variable Explanatory variables DF AICc DAICc AICc w ER

ANOVA SST Colony ? year ? colony 9 year 5 9,016.27 0.00 1.000 1.00

Null model 0 17,598.84 8,582.57 – –

LME LT Year 3 21.43 0.00 1.000 1.00

Null model 1 35.45 14.02 – –

LME ST Colony ? chick age ? colony 9 chick age 6 51.04 0.00 0.537 1.00

Colony ? SST ? colony 9 SST 6 51.34 0.30 0.463 1.16

Null model 1 56.59 5.55 – –

GLME Feeding rate LT 2 422.58 0.00 0.628 1.00

LT ? ST 4 423.63 1.05 0.372 1.69

Null model 1 424.60 2.02 – –

LR Fledging probability Colony ? SST ? colony 9 SST 4 170.76 0.00 1.000 1.00

Null model 1 187.36 16.60 – –

GLM Chick age at fledging Feeding rate 2 1,556.28 0.00 0.473 1.00

Null model 1 1,556.86 0.58 0.354 1.34

Colony ? feeding rate 4 1,558.28 2.00 0.174 2.72

Only selected models with DAICc B 2 and null model are shown. ‘‘Individual’’ was included as a random effect into linear mixed effect (LME)

and generalized linear mixed effect (GLME) models (not shown in the table)

SST, sea surface temperature (�C); LT, long trip duration (h); ST, short trip duration (h), DF, model degrees of freedom; AICc, AIC adjusted for

small sample size; DAICc, difference between the AICc of this model and the AICc of the best model; AICc w, AICc weight representing the

likelihood of this model given the data and the set of candidate models; ER, evidence ratio indicating the relative weight of this model against the

best model

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period (Fig. 4 upper panel). The number of prey items

delivered was considerably low during 2008 in Isfjorden

(*2,000; Fig. 4 upper panel). The daily number of prey

items received by a chick did not seem to correlate with the

daily chick feeding rate (Fig. 5a), but was negatively cor-

related with SST (Fig. 5b). Chick diet was dominated by C.

glacialis at both colonies (Isfjorden [80 %, Magdalenef-

jorden [60 %; Fig. 4 lower panel). Rest of the diet was

formed by C. finmarchicus, C. hyperboreus and other prey

items (mainly krill and amphipods) whose proportion was

on average (all years combined) higher in Magdalenefjor-

den (*22.1, *1.1 and *7.2 %, respectively) than in

Isfjorden (*6.8, *0.35 and *6.5 %, respectively; Fig. 4

lower panel).

Fig. 2 Sea surface temperature (SST �C) in Isfjorden (dots) and

Magdalenefjorden (circles) during the chick rearing period a from

2008 to 2010, and in relation to b ST duration, and c LT duration. In

addition, mean chick age during 48-h watch is shown in (b), and study

year in (c)

Fig. 3 Number of food loads delivered daily to a chick by one parent

in relation to LT duration in Isfjorden (dots) and Magdalenefjorden

(circles). Meaningful trend is indicated with a regression line

Fig. 4 Chick diet content in Isfjorden (I) and Magdalenefjorden

(M) from 2008 to 2010. Total number of prey items (upper) and

proportion (%) of different prey taxa (lower) delivered daily to a

chick by one parent. C. fin = C. finmarchicus, C. gla = C. glacialis,

C. hyp = C. hyperboreus, and Other = other than Calanus spp., e.g.

Thysanoessa spp. and Themisto spp.

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Chick fledging success and age at fledging

Model selection strongly suggested that the probability of a

chick to fledge differed between the two colonies and was

negatively correlated with SST (Table 2): fledging proba-

bility was generally higher in Magdalenefjorden (range

0.91–1.0) with lower SST than in Isfjorden (range

0.62–0.97) with higher SST (Fig. 6). The effect of LT and

ST duration, or daily feeding rate on the fledging proba-

bility was not supported by model selection as models

including these effects were not among the selected models

(Table 2).

Chick’s age at fledging (range 24–26 days; Fig. 6) was

similar throughout the study period at both colonies as

evidenced by model selection (null model was among the

selected models; Table 2). Thereby, very limited support

was shown for the influence of daily feeding rate on

fledging age, and no support at all was shown for the

influence of SST on fledging age as model including SST

was not among the selected models (Table 2).

Discussion

We tested whether little auks adjust their bimodal foraging

strategy and chick provisioning according to local ocean-

ographic conditions and associated prey availability, and

whether these adjustments and conditions affect chick’s

fledging success. We found that regardless of clear spa-

tiotemporal variation in oceanographic conditions and the

quality of foraging ground (SST), little auks neither

adjusted their foraging trip duration nor chick provisioning

rate to balance this variation (i.e. SST was not the main

factor in the selected models). The duration of STs stayed

basically the same, while that of the LTs varied in a similar

manner at both colonies, independent of SST. Since chick

provisioning rates were determined by the duration of LTs,

they were similar at both colonies. However, we did find

that chick’s probability to fledge was negatively correlated

with SST.

Earlier little auk studies support our finding of rather

invariable ST duration (Welcker et al. 2009a, b), but not

the lack of SST influence on LT duration. Instead, they

have shown that little auks increase their LT duration when

the SST increases (Welcker et al. 2009a; Brown et al.

2012), and consequently decrease their chick provisioning

rates (Welcker et al. 2009a). One explanation for why we

did not find any effect of SST on LT duration could be that

little auks were very efficient in finding pockets of cold

water in their foraging area, even if overall foraging con-

ditions were not optimal. Also, little auks may have for-

aged in the areas that were characterized by high

abundance of good quality prey that was not determined by

SST. For example in Magdalenefjorden, little auks have

been shown to forage in the marginal ice zone further north

(Jakubas et al. 2012, 2013). The marginal ice zone is

known for its high primary and secondary production (e.g.

Smith et al. 1990; Hunt 1991). Furthermore, little auks

from Hornsund have been shown to utilize frontal systems

to the west and south of the colony, outside the Hornsund

Fig. 5 Number of prey items

delivered daily to a chick by one

parent in relation to a number of

food loads delivered, and b sea

surface temperature (SST �C) in

Isfjorden (dots) and

Magdalenefjorden (circles)

Fig. 6 Fledging success of hatched chicks in relation to sea surface

temperature (SST �C) in Isfjorden (dots) and Magdalenefjorden

(circles). Chick’s mean age at fledging is shown next to each symbol

(dot/circle)

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fjord, despite the presence of Arctic water masses close to

the colony (Brown et al. 2012; Jakubas et al. 2013). Frontal

areas are often characterized by elevated stocks of phyto-

and zooplankton (Fauchald 2009). Thus, during LTs, little

auks from Magdalenefjorden may have foraged along the

marginal ice zone in the north, and little auks from Isf-

jorden may have sought frontal systems outside the fjord in

the shelf zone where these fronts normally occur (Saloranta

and Svendsen 2001; Walkusz et al. 2009). As the Isfjorden

colony is located deep inside the fjord (Fig. 1), the distance

to the fronts may have been comparable to the distance

from Magdalenefjorden colony to the marginal ice zone.

This could explain the similar duration of LTs at both

colonies. The shorter duration of LTs in 2009 may have

been due to the more southern location of the marginal ice

zone or more drift ice in the fjords (Ice Information Portal;

http://polarview.met.no) and closer location of the fronts.

Much shorter and less variable duration of STs likely

indicates that little auks collected food for their chicks

closer to the colonies than during LTs. This is further

supported by the content of chick meals: C. glacialis,

which is especially abundant on the shelf and fjord waters

of western and northern Spitsbergen (Blachowiak-Samolyk

et al. 2008; Søreide et al. 2008), dominated chick diet at

both colonies. The use of different foraging grounds during

LTs and STs has been previously suggested by Steen et al.

(2007), Brown et al. (2012) and Jakubas et al. (2012).

Furthermore, similar chick provisioning rates at both

colonies were likely due to similarity of distance to util-

izable foraging grounds during LTs—as LT durations,

which influenced the provisioning rates, were similar.

There were, however, differences in the number of prey

items delivered daily to a chick between the colonies. This

number did not correlate with the provisioning rates, but

seemed to be higher when SST was lower: Magdalenef-

jorden chicks received on average 4,200 more prey items

on a daily basis than Isfjorden chicks (all years combined).

This also implies that despite the higher percentage of C.

glacialis in the food portions delivered to chicks in Isf-

jorden, chicks there received generally less C. glacialis

than chicks in Magdalenefjorden. Also, the proportion of

other prey items (C. finmarchicus, C. hyperboreus, and krill

and amphipods) was higher in Magdalenefjorden. Thereby,

it is probable that foraging grounds used to collect food for

the chicks were offering more prey of high quality in the

Magdalenefjorden area than in the Isfjorden area.

Other seabird studies have shown that changes in the

chick provisioning rate and in the content of chick meals

can affect chick’s condition, survival and probability to

fledge (e.g. Schaffner 1990; Brekke and Gabrielsen 1994;

Golet et al. 2000; Davoren and Montevecchi 2003; Kadin

et al. 2012). In our case, we found that chick fledging

success was not affected by provisioning rates, but that

SST had a strong effect on fledging. This effect was likely

related to the prey availability and quality in the little auk’s

foraging grounds. In the Magdalenefjorden area where SST

was lower, chicks received generally more prey of good

quality than chicks in the Isfjorden area where SST was

higher—despite the similar delivery rate of chick meals at

the two colonies. During 1 year, however, fledging success

in the Isfjorden colony was at the similar level with that of

the Magdalenefjorden colony: In that 1 year, SST was

lower (4.70 �C) than during the other two years in the

Isfjorden area (Fig. 6), and Isfjorden chicks received more

good quality C. hyperboreus (biggest species with highest

lipid reserves among the three Calanus species; Scott et al.

2000), and krill and amphipods compared to these other

two years (Fig. 4). This may have increased the fledging

success. Furthermore, there were no differences in chick’s

fledging age. This is in contrast to the recent study by

Jakubas et al. (2013) who found that chicks fledged at an

older age when conditions in foraging grounds were not

optimal.

To conclude, the results of our study suggest that vari-

ation in foraging trips or provisioning rates was not related

to SST. This contrasts the previous studies that found a

negative relationship between SST, trip durations and

provisioning rates (Welcker et al. 2009a; Brown et al.

2012). Search efficiency and access to foraging grounds

known for elevated prey stocks (e.g. the marginal ice zone

and fronts) may have had a greater influence on trip

durations and provisioning rates. Also, little auks seemed

to prioritize self-maintenance over that of their chicks

when foraging conditions so demanded: little auks adjusted

the duration of LTs but not that of STs and provisioned

their chicks at lower rate when duration of LTs increased.

However, these foraging adjustments did not influence

chick’s probability to fledge. Instead, SST had a strong

effect on fledging probability, and this was likely related to

prey availability and quality in the little auk’s foraging

grounds. Our study is a first one to report such a detri-

mental effect of a change in foraging conditions on the

little auk chicks. It is very likely that predicted, warmer

climate in the Arctic (IPCC 2013) and consequential

changes in the little auk’s foraging areas (e.g. change in the

ratio of Arctic vs. Atlantic water masses and disappearance

of sea ice; Falk-Petersen et al. 2007; Stempniewicz et al.

2007) will negatively influence the ability of parents to

provide their chicks, and consequently, the fledging pros-

pects of little auk chicks even more in future.

Acknowledgments This work was supported by a grant from

Norway through the Norwegian Financial Mechanisms Project No.

PNRF-234-AI-1/07(ALKEKONGE) and conducted under the per-

mission of the Governor of Svalbard and Norwegian Animal Research

Authority. We thank Rafał Boehnke for analysing chick diet data

from Magdalenefjorden and Mateusz Barcikowski, Anika Beiersdorf,

Polar Biol

123

Eirik Grønningsæter, Aino Luukkonen, Atle Coward Markussen,

Adam Nawrot, Jan Samołyk, Lech Stempniewicz, Tobias Stal and

Mikko Vihtakari for their invaluable help in the field.

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