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

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
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