Breeding habitat loss reveals limited foraging flexibility and increases foraging effort in a colonial breeding seabird

Background Habitat loss can force animals to relocate to new areas, where they would need to adjust to an unfamiliar resource landscape and find new breeding sites. Relocation may be costly and could compromise reproduction. Methods Here, we explored how the Lesser black-backed gull (Larus fuscus), a colonial breeding seabird species with a wide ecological niche, responds to the loss of its breeding habitat. We investigated how individuals adjusted their foraging behaviour after relocating to another colony due to breeding site destruction, and whether there were any reproductive consequences in the first years after relocation. To this end, we compared offspring growth between resident individuals and individuals that recently relocated to the same colony due to breeding habitat loss. Using GPS-tracking, we further investigated the foraging behaviour of resident individuals in both colonies, as well as that of relocated individuals, as enhanced foraging effort could represent a potential driver of reproductive costs. Results We found negative consequences of relocation for offspring development, which were apparent when brood demand was experimentally increased. Recently relocated gulls travelled further distances for foraging than residents, as they often visited more distant foraging sites used by residents breeding in their natal colony as well as new areas outside the home range of the residents in the colony where they settled. Conclusions Our results imply that relocated individuals did not yet optimally adapt to the new food landscape, which was unexpected, given the social information on foraging locations that may have been available from resident neighbours in their new breeding colony. Even though the short-term reproductive costs were comparatively low, we show that generalist species, such as the Lesser black-backed gull, may be more vulnerable to habitat loss than expected. Long term studies are needed to investigate how long individuals are affected by their relocation in order to better assess potential population effects of (breeding) habitat loss.

Diet segregation in Adélie penguins: some individuals attempt to overcome colony-induced and annual foraging challenges

Intraspecific competition for food can be especially high in colonial breeding seabirds. To minimize colony-induced or annual foraging challenges, diet may vary among individuals, but few studies have simultaneously investigated the effects of both extrinsic conditions (e.g. colony or year effects) and parameters of an individual (e.g. sex, age or individual quality) on diet in seabirds. Using stable isotope analyses, we studied the diet of 214 Adélie penguins Pygoscelis adeliae of known sex, age and breeding quality, nesting in 2 colonies on Ross Island, Antarctica, over 3 breeding seasons. During the study, δ15N and δ13C isotope values were lower in penguins breeding at Cape Crozier compared to those at Cape Bird, revealing a difference in prey proportions. Cape Bird penguins were estimated to consistently consume more energy-rich silverfish Pleuragramma antarctica, while birds at Cape Crozier ate more crystal krill Euphausia crystallorophias. We also found inter-annual differences in diet, with a higher dietary fish proportion in both colonies during 2011. Males had significantly higher δ15N values, indicating a higher fish consumption than females. This sexual segregation in diet was particularly pronounced at Cape Bird, where the overall isotopic niche was wider than at Cape Crozier. Differences in diet among adults of varying ages only existed at Cape Bird, where middle-aged penguins consumed more fish than old and young penguins. This study provides evidence that Adélie penguin diet is largely driven by annual, seasonal and local abundances of prey, with only some individuals selectively foraging for more nutritional prey if prey choices are present.

Author Correction: Important At-Sea Areas of Colonial Breeding Marine Predators on the Southern Patagonian Shelf

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Nestling carcasses from colonially breeding wading birds: patterns of access and energetic relevance for a vertebrate scavenger community

Energy transfer is fundamental to ecosystem processes, affecting productivity and community structure. Large aggregations of colonially breeding birds are known as nutrient sources through deposition of feces, but also may deposit large quantities of energy in the form of dead nestlings. The magnitude and ecological relevance of this process to the scavenger community is poorly understood. We used trail cameras to monitor the fates of size-appropriate chicken carcasses in heron colonies in order to quantify the proportion of available fallen nestlings that were consumed by scavengers in the Everglades of Florida, USA. Overall, 85% of 160 carcasses were consumed, with Turkey Vultures (Cathartes aura, 47%) and American Alligators (Alligator mississippiensis, 29%) being the primary consumers. Probability of consumption by alligators or vultures was related to distance from nest to water, local nesting density, and colony type. Consumption probabilities of both scavengers in relation to habitat covariates suggested clear resource partitioning promoting coexistence. We estimate fallen nestlings throughout this ecosystem could support 16% of the alligator population and 147 adult Turkey Vultures during a nesting season. This work indicates that fallen nestlings can serve as an important source of energy for scavengers at colonial breeding aggregations, particularly in oligotrophic systems.

Expression of obesity-related adipokine genes during fasting in a naturally obese marine mammal

Northern elephant seals ( Mirounga angustirostris) are exceptional among fasting-adapted animals in coupling prolonged fasting with energetically costly activities, relying on oxidation of fat stores accrued during foraging to power metabolic demands of reproduction and molting. We hypothesized that high rates of energy expenditure, insulin resistance, and immune responses to colonial breeding in fasting seals are mediated by adipokines, or signaling molecules secreted by adipose tissue that are associated with obesity and inflammation in humans. We measured mRNA expression of 10 adipokine genes in blubber tissue of adult female elephant seals sampled early and late during their lactation and molting fasts and correlated gene expression with adiposity and circulating levels of corticosteroid and immune markers. Expression of adiponectin ( ADIPOQ) and its receptor ADIPOR2, leptin receptor ( LEPR), resistin ( RETN), retinol binding protein 4 ( RBP4), and visfatin/nicotinamide phosphoribosyltransferase ( NAMPT) was increased, whereas that of fat mass and obesity-associated protein ( FTO) was decreased in late-fasted compared with early-fasted groups. Abundance of adipokine transcripts that increased in late fasting was negatively associated with body mass and positively associated with cortisol, suggesting that they may mediate local metabolic effects of cortisol in blubber during fasting. Expression of several adipokines was correlated with the immune markers IL-6, haptoglobin, IgM, and IgE, suggesting a potential role in modulating immune responses to colonial breeding and molting. Since many of these adipokines have not been measured in other wild animals, this study provides preliminary insights into their local regulation in fat tissue and targeted assays for future studies.