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

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
NEST SITE CHOICE
BY ARCTIC-NESTING COMMON EIDERS
Peter L. F. Fast¹, H. Grant Gilchrist², and Robert G. Clark¹,³
¹ Department of Biology, University of Saskatchewan; peter.fast@gmail.com
²Canadian Wildlife Service and Department of Biology, Carleton University
³Canadian Wildlife Service and Department of Biology, University of Saskatchewan
We investigated patterns of common eider (Somateria mollissima) nest site use in Canada’s Eastern
Arctic, and conducted experiments to better understand selective processes that may underlie
these patterns. We monitored 5 study plots using observation blinds, documenting successful nest
establishment (i.e., laid eggs and onset of incubation) and subsequent nest fate. Following hatch, we
measured physical characteristics of all available nest bowls and random sites. Higher probability
of bowl use occurred in regions of greatest local nesting density, and in bowls with large adjacent
rocks and organic substrates. Furthermore, bowls with these characteristics had a tendency to be
used first. Available nest bowls that were not used by an incubating female (i.e., either no nest
attempted, or nest loss occurring during egg laying) had intermediate characteristics between random
sites and used bowls. Furthermore, we found characteristics positively associated with probability
of use were also associated with increased probability of nest success. These patterns suggest that
nesting eiders actively select and/or lose fewer eggs to predators in sites with certain characteristics.
To investigate these patterns further, we experimentally manipulated nests prior to egg-laying and
during incubation. Extraneous material (e.g. moss, down) placed within bowls prior to laying had no
influence on probability of nest establishment, but bowls containing down were more likely to have
nests successfully initiated in them earlier than nests containing no nesting material. We also placed
artificial nest shelters and temperature probes over established nests. We found females nesting in
artificial shelters experienced more moderate thermal environments, and maintained higher late
incubation body weight. We speculate that it may be energetically advantageous for eiders to nest
in sites with large rocks that provide shelter from strong wind and rain, whereas bowls with rock
substrates likely have poorer insulative properties than those with organic substrates. Furthermore,
eiders may benefit from increased detection of predators and/or reduced nest mortality by choosing
bowls in areas of higher nesting density.
84 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005