Incubating common eiders (Somateria mollissima) insulate their nests with down to maintain desirable heat and humidity for their eggs. Eiderdown has been collected by Icelandic farmers for centuries, and down is replaced by hay during collection. This study determined whether down collecting affected the female eiders or their hatching success. We compared the following variables between down and hay nests: incubation temperature in the nest, incubation constancy, recess frequency, recess duration, egg rotation and hatching success of the clutch. Temperature data loggers recorded nest temperatures from 3 June to 9 July 2006 in nests insulated with down (n = 12) and hay (n = 12). The mean incubation temperatures, 31.5 and 30.7 °C, in down and hay nests, or the maximum and minimum temperatures, did not differ between nest types where hatching succeeded. Cooling rates in down, on average 0.34 °C/min and hay nests 0.44°C/min, were similar during incubation recesses. Females left their nests 0-4 times every 24 h regardless of nest type, for a mean duration of 45 and 47.5 min in down and hay nests, respectively. The mean frequency of egg rotation, 13.9 and 15.3 times every 24 h, was similar between down and hay nests, respectively. Hatching success adjusted for clutch size was similar, 0.60 and 0.67 in down and hay nests. These findings indicate that nest down is not a critical factor for the incubating eider. Because of high effect sizes for cooling rate and hatching success, we hesitate to conclude that absolutely no effects exist. However, we conclude that delaying down collection until just before eggs hatch will minimize any possible effect of down collection on females.
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Acknowledgments Financial support for this work was partly provided by The Icelandic Centre for Research (Rannis) and the Icelandic Eider Farmers Association. The authors wish to thank the owners of Hvallátur in Breidafjordur for allowing us access to the eider colony and Vilhjálmur Thorsteinsson at the Mar. Res. Inst. in Reykjavík for lending the temperature data loggers and assistance with transferring the data to the computer. We thank Snæbjörn Pálsson for his help with statistical tests and Tómas G. Gunnarsson, Arnthór Gardarsson, Páll Hersteinsson, Larry Jocobson, and Gudrún Thórarinsdóttir for comments that improved earlier drafts of this manuscript. We also thank the reviewers Paul Flint, John C. Coulson and Flemming R. Merkel for their improvements to this manuscript.
- Breeding success
- Down collecting
- Incubation behaviour
- Nesting temperature
- Somateria mollissima