Incubation behavior of Spectacled Eiders on the Yukon-Kuskokwim Delta, Alaska

We studied incubation behavior of Spectacled Elders (Somateria fischeri) on the Yukon-Kuskokwim Delta in 1996. We trapped 19 females on their nests an d weighed them in early incubation and again at hatch. Average daily weight loss for incubating females was 16.6 +/- 1.0 g day(-1), which resulted in a cumulative loss of 26% of body weight throughout incubation. Nest attenda nce was monitored for a portion of the incubation period using temperature sensing artificial eggs. Incubation constancy averaged 90 +/- 1%. Average r ecess length was 37.1 +/- 0.9 min and nests cooled an average of 4.2 +/- 0. 1 degrees C during recesses. Recess frequency averaged 2.5 +/- 0.1 recesses day(-1), and most recesses (70%) occurred between 10:00 and 22: 00. Incuba tion constancy varied among females, but was not related to changes in body weight or incubation period. There was no influence of ambient temperature on incubation recess length, however most recesses were taken during the w armest part of the day. We found considerable variation among females in pa tterns of daily incubation constancy, nest cooling, recess frequency, and r ecess length. It is not clear from our results what factors constrain incub ation behavior of Spectacled Elders, but we suggest that individual females respond to a complex suite of variables.