Sexual size dimorphism and timing of spring migration in birds

Sexually selected traits are limited by selection against those traits in other fitness components, such as survival. Thus, sexual selection favouring large size in males should be balanced by higher mortality of larger males. However, evidence from red‐winged blackbirds (Agelaius phoeniceus) indica...

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Bibliographic Details
Published in:Journal of evolutionary biology 2003-01, Vol.16 (1), p.154-162
Main Authors: Kissner, K. J., Weatherhead, P. J., Francis, C. M.
Format: Article
Language:English
Subjects:
Animal Migration - physiology
Animals
Body Constitution
Male
migration
natural selection
Ontario
passerine birds
Phylogeny
Selection, Genetic
Sex Characteristics
sexual selection
sexual size dimorphism
Songbirds - anatomy & histology
Songbirds - physiology
Time Factors
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Summary:Sexually selected traits are limited by selection against those traits in other fitness components, such as survival. Thus, sexual selection favouring large size in males should be balanced by higher mortality of larger males. However, evidence from red‐winged blackbirds (Agelaius phoeniceus) indicates that large males survive better than small males. A survival advantage to large size could result from males migrating north in early spring, when harsh weather favours large size for energetic reasons. From this hypothesis we predicted that, among species, sex differences in body size should be correlated with sex differences in timing of spring migration. The earlier males migrate relative to females, the larger they should be relative to females. We tested this prediction using a comparative analysis of data collected from 30 species of passerine birds captured on migration. After controlling for social mating system, we found that sexual size dimorphism and difference in arrival dates of males and females were significantly positively correlated. This result is consistent with the hypothesis that selection for survival ability promotes sexual size dimorphism (SSD), rather than opposes SSD as is the conventional view. If both natural selection and sexual selection favour large adult males, then limits to male size must be imposed before males become adults.
ISSN:1010-061X
1420-9101
DOI:10.1046/j.1420-9101.2003.00479.x