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Updated: Mar 16, 2026

Visually Sexing Loggerhead Shrike Lanius Ludovicianus Using Plumage Coloration and Pattern
Published on: March 8, 2020
Male-biased sex allocation in ageing parents; a longitudinal study in a long-lived seabird
Oscar Vedder1, Sandra Bouwhuis2, María M Benito3
1Institute of Avian Research 'Vogelwarte Helgoland', An der Vogelwarte 21, 26386, Wilhelmshaven, Germany oscarvedder@hotmail.com.
Abstract:
Optimal sex allocation is frequency-dependent, but senescence may cause behaviour at old age to be suboptimal. We investigated whether sex allocation changes with parental age, using 16 years of data comprising more than 2500 molecularly sexed offspring of more than 600 known-age parents in common terns (Sterna hirundo), slightly sexually size-dimorphic seabirds. We decomposed parental age effects into within-individual change and sex allocation-associated selective (dis)appearance. Individual parents did not differ consistently in sex allocation, but offspring sex ratios at fledging changed from female- to male-biased as parents aged. Sex ratios at hatching were not related to parental age, suggesting sons to outperform daughters after hatching in broods of old parents. Our results call for the integration of sex allocation theory with theory on ageing and demography, as a change in sex allocation with age per se will cause the age structure of a population to affect the frequency-dependent benefits and the age-specific strength of selection on sex allocation.
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