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Energetic consequences of sex-related habitat segregation in wintering American kestrels (Falco
 

Summary: Energetic consequences of sex-related habitat
segregation in wintering American kestrels (Falco
sparverius)
Daniel R. Ardia
Abstract: Behavioural dominance can cause individuals to use less-preferred habitats, with potentially important life-
history consequences. In the American kestrel, Falco sparverius, females exclude males from preferred open areas; I
hypothesized that this sex-related habitat segregation leads to energetic consequences for males. I predicted that males
would show decreased body condition over winter, while females would not, and that females would maintain larger
net-energy surpluses than would males. Working in southeastern Pennsylvania, between 1991 and 1995, I conducted
150 behavioural observations and measured body condition of 235 wintering kestrels. Male kestrels maintained a lower
body condition (residuals of a regression of mass vs. size) than did females and showed a decrease in mean body con-
dition over winter, which females did not. I estimated that females had larger daily energy expenditures than did males
(248 vs. 195 kJ per bird per day, ratio 1.27) but also had larger daily energy intakes (537 vs. 322 kJ/day, ratio 1.67).
Females had larger net energy surpluses than did males (288 vs. 126 kJ/day, ratio 2.27), particularly when temperatures
were <0°C. I conclude that differences in energetics are due in part to habitat differences and that males may suffer
consequences by being forced to use less-preferred habitats.
Résumé : La dominance comportementale peut pousser des individus à utiliser des habitats autres que ceux qu'ils pré-
fèrent, ce qui peut influencer fortement leur biologie. Chez la crécerelle d'Amérique, Falco sparverius, les femelles ex-
cluent les mâles des zones ouvertes, généralement préférées; j'ai posé en hypothèse que cette ségrégation reliée au sexe
avait des conséquences énergétiques pour les mâles. Les mâles, mais pas les femelles, seraient en moins bonne condi-

  

Source: Ardia, Dan - Department of Biology, Franklin and Marshall College

 

Collections: Biology and Medicine