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Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?
Rosenfield, Robert N; Stout, William E; Giovanni, Matthew D; Levine, Noah H; Cava, Jenna A; Hardin, Madeline G; Haynes, Taylor G.
Afiliação
  • Rosenfield RN; Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.
  • Stout WE; W2364 Heather Street Oconomowoc Wisconsin 53066.
  • Giovanni MD; Midwest Ecological Services De Forest Wisconsin 53532.
  • Levine NH; Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.
  • Cava JA; Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.
  • Hardin MG; Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.
  • Haynes TG; Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.
Ecol Evol ; 5(18): 4037-48, 2015 Sep.
Article em En | MEDLINE | ID: mdl-26445658
ABSTRACT
Offspring sex ratios at the termination of parental care should theoretically be skewed toward the less expensive sex, which in most avian species would be females, the smaller gender. Among birds, however, raptors offer an unusual dynamic because they exhibit reversed size dimorphism with females being larger than males. And thus theory would predict a preponderance of male offspring. Results for raptors and birds in general have been varied although population-level estimates of sex ratios in avian offspring are generally at unity. Adaptive adjustment of sex ratios in avian offspring is difficult to predict perhaps in part due to a lack of life-history details and short-term investigations that cannot account for precision or repeatability of sex ratios across time. We conducted a novel comparative study of sex ratios in nestling Cooper's hawks (Accipiter cooperii) in two study populations across breeding generations during 11 years in Wisconsin, 2001-2011. One breeding population recently colonized metropolitan Milwaukee and exhibited rapidly increasing population growth, while the ex-Milwaukee breeding population was stable. Following life-history trade-off theory and our prediction regarding this socially monogamous species in which reversed sexual size dimorphism is extreme, first-time breeding one-year-old, second-year females in both study populations produced a preponderance of the smaller and cheaper sex, males, whereas ASY (after-second-year), ≥2-year-old females in Milwaukee produced a nestling sex ratio near unity and predictably therefore a greater proportion of females compared to ASY females in ex-Milwaukee who produced a preponderance of males. Adjustment of sex ratios in both study populations occurred at conception. Life histories and selective pressures related to breeding population trajectory in two age cohorts of nesting female Cooper's hawk likely vary, and it is possible that these differences influenced the sex ratios we documented for two age cohorts of female Cooper's hawks in Wisconsin.
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Texto completo: 1 Base de dados: MEDLINE Idioma: En Ano de publicação: 2015 Tipo de documento: Article

Texto completo: 1 Base de dados: MEDLINE Idioma: En Ano de publicação: 2015 Tipo de documento: Article