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

SECOND NORTH AMERICAN SEA DUCK CONFERENCE
MODELING THE ENERGETICS OF SPECTACLED EIDERS
DURING LONG-TERM CHANGE
IN ICE AND BENTHOS OF THE BERING SEA
J. R. Lovvorn 1 , J. M. Grebmeier 2 , L. W. Cooper 2 , S. E. Richman 1 , J. K. Bump 1 , and B. I. Sirenko 3
1 Department of Zoology, University of Wyoming, Laramie, WY 82071; lovvorn@uwyo.edu
2 Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN 37996
3 Zoological Institute, Russian Academy of Sciences, St. Petersburg, Russia
The world population of threatened spectacled eiders (Somateria fischeri) winters in the Bering Sea,
where they dive 40–70 m among leads in the pack ice to feed on macrobenthos. Foraging costs relative
to food intake are important to the eiders’ overwinter survival and prebreeding condition. Based on
field, laboratory, and remote sensing studies, we are modeling effects on the eiders’ energy balance
of changes in benthos revealed by periodic sampling from 1950 to present. To estimate costs of deep
dives, biomechanical models were developed based on other species of wing-propelled divers fitted
with time-depth recorders. Mechanical costs were converted to food requirements with efficiencies
derived from oxygen consumption by captive birds diving in tanks. Respirometry showed that use
of “waste” heat from exercising muscles can greatly reduce thermoregulation costs of eiders. In dive
tanks, the eiders’ intake rates of infaunal bivalves varied with shell length and burial depth, as well
as numbers/m2. Although leads frequently open and close, shifting of ice under different weather
conditions had little effect on estimates of daily flight costs, except when southerly winds forced
widespread closing of leads in the southward-moving pack. Eiders collected in the field had eaten
mostly a narrow length class of a single bivalve species, Nuculana radiata. Long-term data suggest
that this bivalve exhibited major recruitment in the late 1980s through early 1990s, but since then
has declined to low levels similar to the 1950s. Based on transect samples during late winter 1999
and 2001, we interpolated continuous grids for different species and sizes of bivalve prey. Longterm
sampling at a subset of stations indicated ranges of availability for modeling different regimes
of bivalve species dominance. Estimates of dive costs and intake rates for varying prey availability
and weather will indicate the potential effects of long-term changes on the overwinter survival and
breeding potential of spectacled eiders.
52 ANNAPOLIS, MARYLAND, USA NOV. 7-11, 2005