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Steenweg R.J.,Dalhousie University | Ronconi R.A.,Dalhousie University | Ronconi R.A.,Grand Manan Whale and Seabird Research Station | Leonard M.L.,Dalhousie University
Condor | Year: 2011

Studies of seabird diets may reveal subtle ways in which sympatric species partition resources to facilitate co-existence. We studied the variability and partitioning of diets between the Herring (Larus argentatus) and Great Black-backed Gulls (L. marinus), both generalist predators, during incubation and early chick rearing on Kent Island, Bay of Fundy, Canada. We assessed diets from pellets collected around nests, regurgitates from captured birds, and stable-isotope analysis of prey items and tissues (blood and feathers) obtained from chicks and adults. Pellet analyses indicated that both species relied primarily on fish (28 to 45% of identified prey items) and crabs (15 to 43%). Stable-isotope analyses showed that the Great Black-backed Gull fed at a higher trophic level than the Herring Gull, both species fed at higher trophic levels during breeding than during nonbreeding, and both species has similar preferences for feeding inshore vs. offshore and in terrestrial vs. marine habitats. Contrary to previous research, we found that chicks were fed from a lower trophic level than where adults feed. Models of isotopic mixing estimating the proportion of assimilated diets were generally consistent with the pellet analysis for adults but revealed that both species fed their chicks more krill (>60%; Meganyctiphanes norvegica) and mackerel (>20%; Scomber scombrus) than adults consumed; adults may selectively provision their young with easily digestible prey and prey of high energy content. Our results reveal evidence of dietary partitioning between species and age classes, and highlight the strengths and biases associated with techniques for sampling gulls' diet. © The Cooper Ornithological Society 2011. Source

Robertson G.J.,Environment Canada | Roul S.,Environment Canada | Allard K.A.,Environment Canada | Pekarik C.,Environment Canada | And 9 more authors.
Waterbirds | Year: 2016

Herring Gull (Larus argentatus) and Great Black-backed Gull (L. marinus) morphometric data from various eastern North American locations was collected to examine the sources of variation in body size within and among geographic regions. For Herring Gulls, significant differences in all commonly taken measurements at local and regional scales were found. However, most of the variation in measurements was due to sex differences and the natural variance seen within local populations. Herring Gulls breeding in the Arctic did not show any evidence of being morphologically different from other groups. A discriminant function derived from a Newfoundland, Canada, breeding population of Herring Gulls successfully assigned the sex of birds in Atlantic Canada and Nunavut, Canada, further emphasizing that most of the variation seen is between sexes and not among local or even regional populations. It also indicates that the evitable variation introduced by inter-individual differences in measurements was insufficient to compromise the utility of the discriminant function. The correct classification rate was lower for Great Lakes breeding Herring Gulls, indicating that these birds have different morphologies than those of populations in easterly regions. In contrast, few differences and no clear geographic patterns were found in measurements for Great Black-backed Gulls. These results were consistent with recent genetic information, suggesting an older west to east radiation of Herring Gulls across North America and a lack of isolation among Great Black-Backed Gull populations. Source

Haman K.H.,University of Georgia | Haman K.H.,Georgia Sea Turtle Center | Norton T.M.,Georgia Sea Turtle Center | Ronconi R.A.,Grand Manan Whale and Seabird Research Station | And 5 more authors.
Journal of Wildlife Diseases | Year: 2013

The Great Shearwater (Puffinus gravis) is an abundant pelagic seabird that undertakes transequatorial migrations between the North and South Atlantic Ocean. This species is a useful indicator of large-scale alterations in marine dynamics due to its wide geographic range, long-distance migrations, and relative abundance. From 1993 to 2011, 12 separate mortality events, with 4, 961 Great Shearwaters recovered, were documented along the eastern coast of the United States. Of these, seven events (n=4, 885) occurred in the Southeast (SE) and five (n=76) in the Northeast (NE) United States. The cause of death was determined either by necropsy (n=60) or external examination (n=4, 901). All Great Shearwaters stranded along the SE United States were emaciated while 58% were emaciated in the NE United States. No plastic was observed in Great Shearwaters in the SE US (n=27), but the gastrointestinal tract of 82% (n=27) of all stranded birds along the NE United States had at least one plastic bead. There was no evidence of infectious disease or heavy metals in stranded Great Shearwaters examined (n=14, from the 2005 SE event). Stable isotope analysis of feathers (n=9, from a 2007 SE event) suggests dietary differences between emaciated stranded birds and live-caught healthy birds. The temporal distribution of stranding detections suggests a general increase in the number of observed Great Shearwater strandings over the past two decades. From 1993 to 2000 there were a total of three mortality events with 296 individualGreat Shearwaters.However, there was a threefold increase in the number of mortality events from 2001 to 2011 (nine events involving 4, 665 individuals). The causes of this apparent increase in strandings are unknown but may be due to an increase in reporting effort over the past two decades combined with changing oceanographic conditions in the South Atlantic Ocean, leading to large-scale mortality of emaciated Great Shearwaters along the east coast of the United States. © Wildlife Disease Association 2013. Source

Fairhurst G.D.,University of Saskatchewan | Bond A.L.,University of Saskatchewan | Bond A.L.,Environment Canada | Bond A.L.,Center for Conservation Science | And 3 more authors.
Ibis | Year: 2015

Diet during the non-breeding period influences condition and subsequent reproduction. Physiological mechanisms underlying such carry-over effects are poorly understood but could be clarified by studying physiological responses to variation in diet during non-breeding. The hormone corticosterone provides a functional link between diet and survival and reproduction, but methodological limitations have prevented previous studies from testing the hypothesis that, on an individual level, avian corticosterone levels during the non-breeding period reflect broader patterns in feeding ecology during that time. Using museum specimens (1859-2002) and live birds (2012), we found that corticosterone from feathers (CORTf) is negatively related to trophic position (TP) inferred from feather stable-nitrogen isotope values (δ15N) in Leach's Storm-petrels Oceanodroma leucorhoa. CORTf was not related to stable-carbon isotope values (δ13C). We detected no temporal trends in CORTf or δ15N, and neither was related to a large-scale index of winter climate, suggesting a general ecological phenomenon rather than a reflection of historical environmental changes. However, we detected a temporal trend in feather δ13C, and δ13C was related to δ15N. Our findings suggest a physiological benefit of feeding at higher TPs, either through increased nutritional value or reduced foraging costs associated with higher TP prey, and future research should aim to distinguish between these two explanations. Nevertheless, ours is the first evidence of a correlation between individual endocrine levels and foraging ecology, and demonstrates non-lethal variation in a physiological mediator in turn related to variation in resource use. © 2014 British Ornithologists' Union. Source

Siders Z.A.,University of Florida | Siders Z.A.,Grand Manan Whale and Seabird Research Station | Westgate A.J.,Grand Manan Whale and Seabird Research Station | Westgate A.J.,University of North Carolina at Wilmington | And 4 more authors.
PLoS ONE | Year: 2013

The local distribution of basking sharks in the Bay of Fundy (BoF) is unknown despite frequent occurrences in the area from May to November. Defining this species' spatial habitat use is critical for accurately assessing its Special Concern conservation status in Atlantic Canada. We developed maximum entropy distribution models for the lower BoF and the northeast Gulf of Maine (GoM) to describe spatiotemporal variation in habitat use of basking sharks. Under the Maxent framework, we assessed model responses and distribution shifts in relation to known migratory behavior and local prey dynamics. We used 10 years (2002-2011) of basking shark surface sightings from July-October acquired during boat-based surveys in relation to chlorophyll-a concentration, sea surface temperature, bathymetric features, and distance to seafloor contours to assess habitat suitability. Maximum entropy estimations were selected based on AICc criterion and used to predict habitat utilizing three model-fitting routines as well as converted to binary suitable/non-suitable habitat using the maximum sensitivity and specificity threshold. All models predicted habitat better than random (AUC values >0.796). From July-September, a majority of habitat was in the BoF, in waters >100 m deep, and in the Grand Manan Basin. In October, a majority of the habitat shifted southward into the GoM and to areas >200 m deep. Model responses suggest that suitable habitat from July - October is dependent on a mix of distance to the 0, 100, 150, and 200 m contours but in some models on sea surface temperature (July) and chlorophyll-a (August and September). Our results reveal temporally dynamic habitat use of basking sharks within the BoF and GoM. The relative importance of predictor variables suggests that prey dynamics constrained the species distribution in the BoF. Also, suitable habitat shifted minimally from July-September providing opportunities to conserve the species during peak abundance in the region. Source

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