Evidence of social information on food location in a ring-billed gull colony, but the birds do not use it

An interspecific foraging association with polar bears increases foraging opportunities for avian predators in a declining Arctic seabird colony

Interspecific foraging associations (IFAs) are biological interactions where two or more species forage in association with each other. Climate-induced reductions in Arctic sea ice have increased polar bear (Ursus maritimus) foraging in seabird colonies, which creates foraging opportunities for avian predators. We used drone video of bears foraging within a common eider (Somateria mollissima) colony on East Bay Island (Nunavut, Canada) in 2017 to investigate herring gull (Larus argentatus) foraging in association with bears. We recorded nest visitation by gulls following n = 193 eider flushing events from nests during incubation. The probability of gulls visiting eider nests increased with higher number of gulls present (β = 0.14 ± 0.03 [SE], p < .001) and for nests previously visited by a bear (β = 1.14 ± 0.49 [SE], p < .02). In our model examining the probability of gulls consuming eggs from nests, we failed to detect statistically significant effects for the number of gulls present (β = 0.09 ± 0.05 [SE], p < .07) or for nests previously visited by a bear (β = -0.92 ± 0.71 [SE], p < .19). Gulls preferred to visit nests behind bears (χ2 = 18, df = 1, p < .0001), indicating gulls are risk averse in the presence of polar bears. Our study provides novel insights on an Arctic IFA, and we present evidence that gulls capitalize on nests made available due to disturbance associated with foraging bears, as eiders disturbed off their nest allow gulls easier access to eggs. We suggest the IFA between gulls and polar bears is parasitic, as gulls are consuming terrestrial resources which would have eventually been consumed by bears. This finding has implications for estimating the energetic contribution of bird eggs to polar bear summer diets in that the total number of available clutches to consume may be reduced due to avian predators.

Consistent sociality but flexible social associations across temporal and spatial foraging contexts in a colonial breeder

When the consequences of sociality differ depending on the state of individual animals and the experienced environment, individuals may benefit from altering their social behaviours in a context-dependent manner. Thus, to fully address the hypotheses about the role of social associations it is imperative to consider the multidimensional nature of sociality by explicitly examining social associations across multiple scales and contexts. We simultaneously recorded > 8000 associations from 85% of breeding individuals from a colony of Australasian gannets (Morus serrator) over a 2-week period, and examined gregariousness across four foraging states using multilayer social network analysis. We found that social associations varied in a context-dependent manner, highlighting that social associations are most prevalent during foraging (local enhancement) and in regions expected to provide clustered resources. We also provide evidence of individual consistency in gregariousness, but flexibility in social associates, demonstrating that individuals can adjust their social behaviours to match experienced conditions.

Landfills represent significant atmospheric sources of exposure to halogenated flame retardants for urban-adapted gulls

Halogenated flame retardants (HFRs) are contaminants that are abundantly emitted from waste management facilities (WMFs) and that became ubiquitous in air of urbanized regions. Urban birds including gulls have adapted to exploiting human food resources (refuse) in WMFs, and have thus experienced population explosions worldwide. However, foraging in WMFs for birds may result in exposure to HFRs that have been shown to be toxic for animals. The objective of this study was to determine the influence of foraging near or in various WMFs on the atmospheric exposure of birds to HFRs, and to localize other sources of HFRs at the regional scale in a highly urbanized environment. We measured the atmospheric exposure to HFRs in one of the most abundant gull species in North America, the ring-billed gull (Larus delawarensis), breeding in the densely-populated Montreal area (Canada) using a novel approach combining bird-borne GPS dataloggers and miniature passive air samplers (PASs). We determined concentrations of 11 polybrominated diphenyl ethers (PBDEs) and three emerging HFRs of high environmental concern in PASs carried by gulls. We show that the daily sampling rates (pg/day) of PBDEs in PASs were highest in gulls foraging in or around landfills, but were not influenced by meteorological variables. In contrast, the daily sampling rates of emerging HFRs were lower compared to PBDEs and were not influenced by the presence of gulls in or near WMFs. This study demonstrates that atmospheric exposure to HFRs and perhaps other semi-volatile contaminants is underestimated, yet important for birds foraging in landfills.

Evidence of sociality in the timing and location of foraging in a colonial seabird

Social foraging behaviours, which range from cooperative hunting to local enhancement, can result in increased prey capture and access to information, which may significantly reduce time and energy costs of acquiring prey. In colonial species, it has been proposed that the colony itself may act as a site of social information transfer and group formation. However, conclusive evidence from empirical studies is lacking. In particular, most studies in colonial species have generally focussed on behaviours either at the colony or at foraging sites in isolation, and have failed to directly connect social associations at the colony to social foraging. In this study, we simultaneously tracked 85% of a population of Australasian gannets (Morus serrator) over multiple foraging trips, to study social associations at the colony and test whether these associations influence the location of foraging sites. We found that gannets positively associate with conspecifics while departing from the colony and that co-departing gannets have more similar initial foraging patches than individuals that did not associate at the colony. These results provide strong evidence for the theory that the colony may provide a source of information that influences foraging location.

Assessment of individual and conspecific reproductive success as determinants of breeding dispersal of female tree swallows: A capture-recapture approach

Breeding dispersal is a key process of population structure and dynamics and is often triggered by an individual's breeding failure. In both colonial and territorial birds, reproductive success of conspecifics (RSc) can also lead individuals to change breeding sites after a failure on a site. Yet, few studies have simultaneously investigated the independent contribution of individual reproductive success (RSi) and of RSc on dispersal decision. Here, we develop a modeling framework to disentangle the effects of RSi and RSc on demographic parameters, while accounting for imperfect individual detection and other confounding factors such as age or dispersal behavior in the previous year. Using a 10‐year capture–recapture dataset composed of 1,595 banded tree swallows, we assessed the effects of nonmanipulated RSi and RSc on female breeding dispersal in this semicolonial passerine. Dispersal was strongly driven by RSi, but not by RSc. Unsuccessful females were 9.5–2.5 times more likely to disperse than successful ones, depending if they had dispersed or not in the previous year, respectively. Unsuccessful females were also three times less likely to be detected than successful ones. Contrary to theoretical and empirical studies, RSc did not drive the decision to disperse but influenced the selection of the following breeding site once dispersal had been initiated. Because detection of individuals was driven by RSi, which was positively correlated to RSc, assuming a perfect detection as in previous studies may have lead us to conclude that RSc affected dispersal patterns, yet our approach corrected for this bias. Overall, our results suggest that the value and use of RSc as public information to guide dispersal decisions are likely dictated by multiple ecological determinants, such as landscape structure and extent, if this cue is indeed used.

Sequential phenotypic constraints on social information use in wild baboons

Social information allows the rapid dissemination of novel information among individuals. However, an individual's ability to use information is likely to be dependent on phenotypic constraints operating at three successive steps: acquisition, application, and exploitation. We tested this novel framework by quantifying the sequential process of social information use with experimental food patches in wild baboons (Papio ursinus). We identified phenotypic constraints at each step of the information use sequence: peripheral individuals in the proximity network were less likely to acquire and apply social information, while subordinate females were less likely to exploit it successfully. Social bonds and personality also played a limiting role along the sequence. As a result of these constraints, the average individual only acquired and exploited social information on.

Field Metabolic Rate Is Dependent on Time-Activity Budget in Ring-Billed Gulls (Larus delawarensis) Breeding in an Anthropogenic Environment

Environmental and behavioral factors have long been assumed to affect variation in avian field metabolic rate (FMR). However, due to the difficulties in measuring continuous behavior of birds over prolonged periods of time, complete time-activity budgets have rarely been examined in relation to FMR. Our objective was to determine the effect of activity (measured by detailed time-activity budgets) and a series of extrinsic and intrinsic factors on FMR of the omnivorous ring-billed gull (Larus delawarensis). The experiment was conducted during the incubation period when both members of the pair alternate between attending the nest-site and leaving the colony to forage in aquatic and anthropogenic environments (city, agricultural). FMR was determined using the doubly labeled water method. Time-activity budgets were extrapolated from spatio-temporal data (2-5 days) obtained from bird-borne GPS data loggers. Gulls had low FMRs compared to those predicted by allometric equations based on recorded FMRs from several seabird species. Gulls proportioned their time mainly to nest-site attendance (71% of total tracking time), which reduced FMR/g body mass, and was the best variable explaining energy expenditure. The next best variable was the duration of foraging trips, which increased FMR/g; FMR/g was also elevated by the proportion of time spent foraging or flying (17% and 8% of tracking time respectively). Most environmental variables measured did not impact FMR/g, however, the percent of time birds were subjected to temperatures below their lower critical temperature increased FMR. Time-activity budgets varied between the sexes, and with temperature and capture date suggesting that these variables indirectly affected FMR/g. The gulls foraged preferentially in anthropogenic-related habitats, which may have contributed to their low FMR/g due to the high availability of protein- and lipid-rich foods. This study demonstrates that activities were the best predictors of FMR/g in ring-billed gulls, thus providing strong support for this long-standing theory in bioenergetics.

Information use in colonial living

Despite the fact that many animals live in groups, there is still no clear consensus about the ecological or evolutionary mechanisms underlying colonial living. Recently, research has suggested that colonies may be important as sources of social information. The ready availability of information from conspecifics allows animals to make better decisions about avoiding predators, reducing brood parasitism, migratory phenology, mate choice, habitat choice and foraging. These choices can play a large part in the development and maintenance of colonies. Here we review the types of information provided by colonial animals and examine the different ways in which decision-making in colonies can be enhanced by social information. We discuss what roles information might take in the evolution, formation and maintenance of colonies. In the process, we illustrate that information use permeates all aspects of colonial living.

Foraging specificity and prey utilization: evaluating social and memory-based strategies in seabirds

This study explores the capacity for seabirds to exhibit behavioral plasticity in response to the predictability of resources. Using direct species-comparisons, I tested the hypothesis that roseate terns (Sterna dougallii), dietary specialists, rely more heavily on foraging site-fidelity to pursue persistent prey, whereas common terns (S. hirundo), prey generalists, depend more on local enhancement by exploiting mixed-species assemblages. I analysed chick-provisioning observations and the bearings of commuting trajectories between the shared breeding colony, foraging areas, and feeding flocks. Foraging route patterns in roseate terns were consistent with a strategy based more heavily on spatial memory than social cues, in contrast to common terns, which associated more readily with nearby feeding aggregations, in line with social facilitation. Only during years of high prey abundance did roseate terns outperform common terns in nest productivity and the quality of prey delivered to chicks, suggesting that opportunistic tactics support resilience to sparse prey availability.

Balancing energy budget in a central-place forager: which habitat to select in a heterogeneous environment?

Foraging animals are influenced by the distribution of food resources and predation risk that both vary in space and time. These constraints likely shape trade-offs involving time, energy, nutrition, and predator avoidance leading to a sequence of locations visited by individuals. According to the marginal-value theorem (MVT), a central-place forager must either increase load size or energy content when foraging farther from their central place. Although such a decision rule has the potential to shape movement and habitat selection patterns, few studies have addressed the mechanisms underlying habitat use at the landscape scale. Our objective was therefore to determine how Ring-billed gulls (Larus delawarensis) select their foraging habitats while nesting in a colony located in a heterogeneous landscape. Based on locations obtained by fine-scale GPS tracking, we used resource selection functions (RSFs) and residence time analyses to identify habitats selected by gulls for foraging during the incubation and brood rearing periods. We then combined this information to gull survey data, feeding rates, stomach contents, and calorimetric analyses to assess potential trade-offs. Throughout the breeding season, gulls selected landfills and transhipment sites that provided higher mean energy intake than agricultural lands or riparian habitats. They used landfills located farther from the colony where no deterrence program had been implemented but avoided those located closer where deterrence measures took place. On the other hand, gulls selected intensively cultured lands located relatively close to the colony during incubation. The number of gulls was then greater in fields covered by bare soil and peaked during soil preparation and seed sowing, which greatly increase food availability. Breeding Ring-billed gulls thus select habitats according to both their foraging profitability and distance from their nest while accounting for predation risk. This supports the predictions of the MVT for central-place foraging over large spatial scales.

Effect of habitat use and diet on the gastrointestinal parasite community of an avian omnivore from an urbanized environment

With urbanization, anthropogenic foods have grown in importance for several species. A shift away from natural foods is likely to affect trophically transmitted parasites, although this has received limited attention in urban-adapted avian omnivores. We examined the effect of habitat use and diet on gastrointestinal parasite assemblages of Ring-billed Gulls (Larus delawarensis Ord, 1815) breeding in an urbanized region (Montréal, Quebec, Canada) using three approaches depicting different temporal scales. Birds were fitted with global positioning system data loggers to determine habitat-use patterns during a 2–3 day period. Stomach contents were examined, providing dietary information during the preceding hours. Liver carbon (δ13C) and nitrogen (δ15N) stable isotope signatures served as proxy of nutrient assimilation during the preceding 10 days. Endoparasite community variations were best explained by δ13C and δ15N ratios. Individuals with lower δ15N had lower parasite abundance, while δ13C was enriched in birds with less diverse parasites (fewer helminth genera). Tissue depletion in15N in Ring-billed Gulls from this colony has previously been associated with predominant consumption of human-related foods. The present study supports the hypothesis that Ring-billed Gulls exhibiting preference for anthropogenic food sources encounter fewer trophically transmitted parasites, which may have contributed, in part, to their population expansion during the last century.

Combined usage of stable isotopes and GPS-based telemetry to understand the feeding ecology of an omnivorous bird, the Ring-billed Gull (Larus delawarensis)

The aim of the present study was to investigate the feeding ecology of an omnivorous bird, the Ring-billed Gull (Larus delawarensis Ord, 1815), breeding in a highly urbanized and heterogeneous landscape (Montréal area, Quebec, Canada). We used gastrointestinal (G.I.) tract content analysis, GPS-based tracking information, and stable isotope profiles of carbon (δ13C) and nitrogen (δ15N) in selected tissues and major food items. Based on GPS tracking data (1–3 days), Ring-billed Gulls were categorized according to their use of three main foraging habitats: agricultural, St. Lawrence River, and anthropogenic (comprising urban areas, landfills, and wastewater treatment plant basins). Ring-billed Gulls that foraged predominantly in anthropogenic habitats exhibited significantly lower δ15N in blood cells and higher total C to N ratios (C:N) in liver. These lower δ15N and higher C:N ratios were characteristic of profiles determined in food items consumed by Ring-billed Gulls at these urbanized sites (e.g., processed foods). The strong positive correlations between δ13C and δ15N in Ring-billed Gull tissues (plasma, blood cells, and liver) that differed in isotopic turnover times, as well as the strong positive correlations in both δ13C and δ15N between tissue pairs, indicated that Ring-billed Gulls exhibited conserved dietary habits throughout the nesting period. This study demonstrates that combining conventional dietary examination, tissue stable isotope analysis, and fine-scale GPS tracking information may improve our understanding of the large intrapopulation variations in foraging behaviour (and isotopic profiles) commonly observed in omnivorous birds.