The stress hormone corticosterone in a marine top predator reflects short‐term changes in food availability

Citation: Barger, C. P., R. C. Young, A. Will, M. Ito, and A. S. Kitaysky. 2016. Resource partitioning between sympatric seabird species increases during chick-rearing. Ecosphere 7(9):e01447. 10. 1002/ecs2.1447 Abstract. Partitioning of resources by competing species of seabirds may increase during periods of food shortages and elevated energy demands. Here, we examined whether food resource partitioning (differential use of foraging habitat or the consumption of different prey species) between common murres (COMU, Uria aalge) and thick-billed murres (TBMU, U. lomvia) breeding on the same colony in the Bering Sea increases with a predictable increase in energy demands between the incubation and chick-rearing stages of reproduction. We assessed the seasonal dynamics of food availability via corticosterone (CORT) levels and examined adult diet (via stable isotope analysis of nitrogen and carbon, SI) and chick diets (based on nest observations). We compared chick provisioning patterns and examined the characteristics of parental foraging habitat via deployment of bird-borne temperature-depth recorders. We found that CORT levels remained low and similar between the species and reproductive stages, reflecting relatively stable and favorable foraging conditions for both murre species during the study period. Comparisons of SI between murres and their potential prey indicated that diets were similar between the species during incubation and diverged during chick-rearing. Chick-rearing common and thick-billed murres also used different foraging habitats, as reflected in travel distances to foraging areas and sea surface temperature distributions of their foraging dives. TBMUs performed shorter foraging trips, deeper dives and delivered squid to their chicks, while COMUs foraged farther from the colony, performed shallower dives, and delivered fish species to their chicks. These results suggest that food resource partitioning between murre species increased during chick-rearing under favorable foraging conditions. Whether the dietary segregation reflected species-specific differences in adults' foraging efficiency, differences in chicks' dietary requirements, or was a way of reducing competition remains unknown. Regardless of the causal mechanism(s), food resource partitioning might ameliorate interspecific competition between sympatrically breeding birds during periods of increased energy demands.

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“…, Barrett et al. ), which in turn mediates the changes in foraging behavior (Angelier et al. , , Barger and Kitaysky ).…”

Section: Introductionmentioning

confidence: 99%

“…, Barrett et al. ). A previous study demonstrated that stressful food shortages (years when baseline CORT was elevated) resulted in increased interspecific trophic niche partitioning between murre species during incubation; that is, stable isotopic signatures diverged between species during food‐limited periods (Barger and Kitaysky ).…”

Section: Introductionmentioning

confidence: 99%

Resource partitioning between sympatric seabird species increases during chick‐rearing

et al. 2016

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“…; Barrett et al. ), negatively impact reproductive performance and adult nutritional status (Dorresteijn et al. ; Barrett et al.…”

Section: Introductionmentioning

confidence: 99%

“…Some studies find no evidence that changes in prey quality affect reproductive output (Jodice et al 2006;Kadin et al 2012;Hjernquist and Hjernquist, 2010). Others clearly demonstrate that low-quality prey, such as fisheries offal (Gr emillet et al 2008), or changes in the energy content, availability, or abundance of a preferred energy-rich prey species (Wanless et al 2007;Dorresteijn et al 2012;Barrett et al 2015), negatively impact reproductive performance and adult nutritional status (Dorresteijn et al 2012;Barrett et al 2015).…”

Section: Introductionmentioning

confidence: 99%

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

Will

Watanuki

Kikuchi

et al. 2015

Ecology and Evolution

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Changes in climate and anthropogenic pressures might affect the composition and abundance of forage fish in the world's oceans. The junk‐food hypothesis posits that dietary shifts that affect the quality (e.g., energy content) of food available to marine predators may impact their physiological state and consequently affect their fitness. Previously, we experimentally validated that deposition of the adrenocortical hormone, corticosterone, in feathers is a sensitive measure of nutritional stress in seabirds. Here, we use this method to examine how changes in diet composition and prey quality affect the nutritional status of free‐living rhinoceros auklets (Cerorhinca monocerata). Our study sites included the following: Teuri Is. Japan, Middleton Is. central Gulf of Alaska, and St. Lazaria Is. Southeast Alaska. In 2012 and 2013, we collected “bill loads” delivered by parents to feed their chicks (n = 758) to document dietary changes. We deployed time–depth–temperature recorders on breeding adults (n = 47) to evaluate whether changes in prey coincided with changes in foraging behavior. We measured concentrations of corticosterone in fledgling (n = 71) and adult breeders' (n = 82) feathers to determine how birds were affected by foraging conditions. We found that seasonal changes in diet composition occurred on each colony, adults dove deeper and engaged in longer foraging bouts when capturing larger prey and that chicks had higher concentrations of corticosterone in their feathers when adults brought back smaller and/or lower energy prey. Corticosterone levels in feathers of fledglings (grown during the breeding season) and those in feathers of adult breeders (grown during the postbreeding season) were positively correlated, indicating possible carryover effects. These results suggest that seabirds might experience increased levels of nutritional stress associated with moderate dietary changes and that physiological responses to changes in prey composition should be considered when evaluating the effect of prey quality on marine predators.

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“…Food availability has a pronounced effect on stress levels within individuals (Maxwell et al 1992;Clinchy et al 2004;Hinam & St. Clair 2008;Barrett et al 2015). Variation in food abundance was the best predictor of GCs in the common murre (Uria aalge; Kitaysky et al 2007).…”

Section: Using Physiological Measures To Understand Mechanisms Causinmentioning

confidence: 99%

Why are woodland-dependent avian insectivore populations vulnerable to declines in highly-modified landscapes?

Cosgrove¹

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Habitat loss, fragmentation, and degradation are the leading causes of faunal population declines.Substantial effort has been invested in identifying how these landscape changes are related to population parameters. However, to effectively mitigate declines, we must understand the underlying mechanisms impacted by landscape change. Woodland-dependent avian insectivores seem particularly vulnerable, and decline at rates disproportionately greater than other foraging guilds. This pattern suggests that reduced food availability in less-wooded landscapes may be a contributing factor. However, the evidence supporting this hypothesis is sparse. I adopted a multidisciplinary approach to investigate the mechanisms driving population changes of an avian insectivore in highly-modified landscapes by integrating physiological indices with measures of prey availability and landscape structure. First, I presented a framework for conceptualising how the spatiotemporal scale of fragmentation influences the mechanisms impacting populations. I then used the eastern yellow robin (Eopsaltria australis) in the Brigalow Belt South bioregion of southern Queensland to test the importance of local and landscape factors on robin site occupancy, prey density, and robin condition. I also investigated whether an index of chronic stress could be used to predict changes to robin occurrence and identify potential threats to the population. I concluded this work by conducting a supplementary feeding experiment to determine whether food availability was causing the variation in robin condition. A pilot study conducted in the study region four years earlier found that robins were more physiologically stressed (had higher heterophil:lymphocyte ratios) in sites with less woodland in the surrounding landscape, but site occupancy was unrelated to woodland cover. Re-examining the same study system, I established that woodland cover was now the strongest predictor of iii occupancy. While woodland cover at a local scale (within 500 m) was important for robin persistence, woodland cover at a broader scale relevant to dispersal movements (within 5 km) was not. While my stress index could not accurately predict the precise locations of future extirpations, patterns of stress indices (birds were more stressed where woodland cover was lower) did foreshadow a change to the pattern of occurrence. Extirpations from sites with low levels of woodland cover were balanced by colonisations of more-wooded sites. Surprisingly, I found that arthropod prey density was greater at sites that had less surrounding woodland. This result was primarily driven by a large number of Formicidae (ants). However, Formicidae have low nutritional value and once they were excluded from the results, soil moisture, not woodland cover, became the primary determinant of arthropod density. I predicted that robin condition would be strongly associated with arthropod density, but this was not the case. Instead, robins had elevated stress levels at sites with apparently more-favourable...

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The stress hormone corticosterone in a marine top predator reflects short‐term changes in food availability

Cited by 22 publications

References 50 publications

Resource partitioning between sympatric seabird species increases during chick‐rearing

Resource partitioning between sympatric seabird species increases during chick‐rearing

Feather corticosterone reveals stress associated with dietary changes in a breeding seabird

Why are woodland-dependent avian insectivore populations vulnerable to declines in highly-modified landscapes?

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