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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 RN, Stout WE, Giovanni MD, Levine NH, Cava JA, Hardin MG, Haynes TG - Ecol Evol (2015)

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.

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.

No MeSH data available.


Model‐predicted estimates of proportion male nestlings for breeding female Cooper's hawks at Milwaukee and ex‐Milwaukee sites from 2001 to 2011, Wisconsin, USA.
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ece31674-fig-0001: Model‐predicted estimates of proportion male nestlings for breeding female Cooper's hawks at Milwaukee and ex‐Milwaukee sites from 2001 to 2011, Wisconsin, USA.

Mentions: The most probable generalized linear model for predicting temporal variation in annual proportion male nestlings from 2001 through 2011 included interacting variables for “Year” and “Site” (Table 2). Model‐predicted annual proportion male nestlings increased at the ex‐Milwaukee site (βYear*Ex‐Mil = 0.10, 85% CI = 0.05–0.15) but was stable at the Milwaukee site (βYear*Mil = 0.16, 85% CI = −0.09 to 0.40) (Fig. 1).


Does breeding population trajectory and age of nesting females influence disparate nestling sex ratios in two populations of Cooper's hawks?

Rosenfield RN, Stout WE, Giovanni MD, Levine NH, Cava JA, Hardin MG, Haynes TG - Ecol Evol (2015)

Model‐predicted estimates of proportion male nestlings for breeding female Cooper's hawks at Milwaukee and ex‐Milwaukee sites from 2001 to 2011, Wisconsin, USA.
© Copyright Policy - creativeCommonsBy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4588665&req=5

ece31674-fig-0001: Model‐predicted estimates of proportion male nestlings for breeding female Cooper's hawks at Milwaukee and ex‐Milwaukee sites from 2001 to 2011, Wisconsin, USA.
Mentions: The most probable generalized linear model for predicting temporal variation in annual proportion male nestlings from 2001 through 2011 included interacting variables for “Year” and “Site” (Table 2). Model‐predicted annual proportion male nestlings increased at the ex‐Milwaukee site (βYear*Ex‐Mil = 0.10, 85% CI = 0.05–0.15) but was stable at the Milwaukee site (βYear*Mil = 0.16, 85% CI = −0.09 to 0.40) (Fig. 1).

Bottom Line: 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.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology University of Wisconsin Stevens Point Wisconsin 54481.

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.

No MeSH data available.