Egg adoption can explain joint egg-laying in common eiders |
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Authors: | Gregory J Robertson |
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Institution: | (1) Canadian Wildlife Service, 6 Bruce Street, Mount Pearl, NF AIN 4T3, Canada e-mail: grog.robertson@ec.gc.ca, Tel.: +1-709-7727456, Fax: +1-709-7725097, CA |
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Abstract: | Hypotheses regarding the evolution and maintenance of intraspecific nest parasitism were tested with data collected during
a 3-year study of common eiders (Somateria mollissima) breeding near Churchill, Manitoba. The nest parasitism rate was highest (42.4% of nests) during the year with the highest
nest density and the best environmental conditions, and lowest (20.2% of nests) in the year with the lowest nest density and
the poorest environmental conditions. Over the nesting season, parasitic eggs were laid at the same time as normally laid
eggs. Most parasitic eggs (>75%) were laid before the host female laid her third egg. The majority of the parasitic eggs were
the first or second egg produced by the parasitic female. When a parasitic egg was laid before or on the same day as the host
female initiated her clutch, the probability of her first egg being depredated before incubation was significantly lowered.
First- and second-laid eggs suffered a high rate of predation probably because nesting females do not attend their clutch
until their second or third egg is laid. Hypotheses that some females use intraspecific nest parasitism to parasitize the
parental care of other females were inconsistent with these data. Egg adoption is a likely explanation for the prevalence
of females incubating parasitic eggs in this population.
Received: 30 September 1997 / Accepted after revision: 6 May 1998 |
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Keywords: | Common eider Somateria mollissima Intraspecific nest parasitism Brood amalgamation Alternative reproductive behaviours |
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