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High interannual variation in the hatching sex ratio of Tengmalm's owl broods during a vole cycle
Author(s) -
Hipkiss Tim,
Hörnfeldt Birger
Publication year - 2004
Publication title -
population ecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.819
H-Index - 59
eISSN - 1438-390X
pISSN - 1438-3896
DOI - 10.1007/s10144-004-0195-7
Subject(s) - sex ratio , vole , biology , brood , hatching , zoology , ecology , demography , population , sociology
The sex ratio at hatching in broods of Tengmalm's owl ( Aegolius funereus ) in northern Sweden was investigated for 3 years characterized by different phases of the vole and owl cycle. Previous work showed the sex ratio in this species to be male‐biased for 1 year with a favourable food supply, and that in feeding experiments male nestlings (but not females) suffered higher mortality when food was limited, but not otherwise. Here we present data from a complete 3‐year owl cycle, showing that mean brood sex ratio varied significantly among years, being male‐biased (65% males) in the first year of high owl breeding density, unbiased (49%) in the second year of high owl breeding density, and female‐biased (33% males) in the owls’ low year. Brood sex ratio did not vary significantly within years with laying date or parental age. Vole availability, and therefore the owls’ food supply, declined during the 3 years studied. Tengmalm's owl parents thus appear to adaptively adjust the sex ratio of their broods according to the expected annual mortality risk of sons.