Second North American Sea Duck Conference - Patuxent Wildlife ...

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SECOND NORTH AMERICAN SEA DUCK CONFERENCE FORAGING ECOLOGY OF COMMON EIDER DUCKS WINTERING IN THE CANADIAN ARCTIC: THE ROLE OF BIOTIC AND ABIOTIC PROCESSES Joel P. Heath, H. Grant Gilchrist, and Ronald C. Ydenberg Simon Fraser University; joel_heath@sfu.ca The Hudson Bay eider duck (Somateria mollissima) is a unique race which has abandoned longdistance migration to winter in sea ice habitats in Hudson Bay. This environment presents unique challenges for eiders attempting to balance their energy budgets in winter, particularly during heavy sea ice conditions observed in recent years (potentially associated with cooling climate trends in the eastern Canadian arctic). We show that while tidal currents are necessary to maintain persistent open water habitats (polynyas), strong currents also increase the time and energy costs of eiders diving to the sea floor to access benthic prey. Currents can exceed critical velocities (Vcrit) beyond which diving is no longer an energetically profitable activity. At velocities stronger than Vcrit, eider ducks get out of the water to rest on the ice edge. At current velocities lower that Vcrit, data from underwater video of diving eiders indicate that travel time increases while bottom time decreases with increasing current velocity. These results agree with predictions of existing oxygen balance/dive cycle models. However, surface pause durations and observed longer-term behavioral patterns cannot be explained in terms of diving behavior alone. When the entire tide cycle and the time scale over which digestive processing of benthic prey are considered in a dynamic framework, complex and seemingly counterintuitive behavioral patterns of eiders can be understood as adaptive. Specifically, eiders appear to structure their foraging activity in a manner which allows maximizing net energy gain within the overlapping rates of the tidal cycle and digestive processing. This has important implications for understanding energy budgets and survival strategies of wintering sea ducks, elucidating potential impacts of climatic change on wintering populations, and more generally highlights the need of incorporating a multi-scale approach for measuring and understanding temporal activity patterns of sea ducks. 54 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005
Benoît Bruneau and Magella Guillemette SECOND NORTH AMERICAN SEA DUCK CONFERENCE COMMON EIDERS DIVING IN THE DARK: HOW IMPORTANT AND EFFICIENT IS IT? University du Quebec à Rimouski; benoit_bruneau@uqar.qc.ca The question of night foraging is an important one for understanding the ecology of sea ducks since many populations are wintering at high latitude and reduced daylight may severely constraint foraging. Preliminary screening of data stemming from data loggers that record depth and diving schedules showed that diving during the night is a common practice in female common eiders (Somateria mollissima) wintering in the Baltic. In this paper, our objectives are (1) to quantify diurnal and nocturnal diving activity for two periods varying in daylight and (2) test the efficiency of night foraging by comparing nocturnal and diurnal diving performances. Twenty data loggers were deployed on a nesting colony in the Baltic (Christians’ Island, 55 o N) in spring 2003 and 17 were recovered one year later. The loggers were embedded with time-depth recorders recording data every two seconds. Fourteen of them recorded data continuously for 220 days. Night foraging will be quantified for the summer (>12 h) and the winter (< 12 h). In addition, nocturnal diving activity will be determined along a gradient of decreasing daylight from 12 h in September to 7 h in mid-December. Diving activity will be assessed using the number of dives, diving depth, time being submerged and time spent on the bottom. Feeding bouts will be considered as the fundamental unit for analysis. The efficiency of nocturnal diving versus diurnal diving will be compared using the relationship between bottom time and diving depth. For a same depth, a more efficient dive should result as a longer bottom time. Results of this analysis will be presented at the conference. NOV. 7-11, 2005 ANNAPOLIS, MARYLAND, USA 55
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