Temporal patterns in prey size between sexes in a raptor with extreme size dimorphism: testing the intersexual competition hypothesis using web-sourced photographs

This is a Preprint and has not been peer reviewed. This is version 3 of this Preprint.


Download Preprint


Connor T. Panter, arjun amar


In most vertebrates, males are larger than females. For raptors, sexual size dimorphism is reversed, with females being larger. Reversed sexual dimorphism (RSD) in raptors is strongly linked to diet, with species feeding on the most agile prey, for example bird-eating raptors, showing the greatest size differences between the sexes. Hypotheses for reversed sexual dimorphism (RSD) include the ‘intersexual competition’ hypothesis, which proposes that RSD evolved to enable pairs to expand their dietary niche (taking a wider range of prey sizes) during the nestling period when both sexes occupy and hunt within the same territory, and thereby reduce competition between the sexes. If intersexual competition is responsible for the evolution of RSD, we predict that sex-related differences in prey size and dietary niche breadth will be particularly pronounced during the nestling period (cf. the non-nestling period). We explore this prediction in the highly dimorphic Eurasian Sparrowhawk (Accipiter nisus), which displays the largest degree of RSD of all raptors, using web-sourced photographs to identify diet throughout the entire year. We analysed 666 photographs of sparrowhawks on their prey over time. In contrast to our predictions, sex-specific prey sizes were most similar during the nestling period compared to any other time of the year. Both males and females reduced the size of their prey during the nestling period which may be a result of the ‘ingestion rate’ hypothesis, or a strategy employed to prevent hunting-related injuries during this critical period of the year.




Animal Sciences, Behavior and Ethology, Ecology and Evolutionary Biology, Evolution, Life Sciences, Ornithology, Zoology


Accipiter nisus, citizen science, diet, diet analysis, niche breadth, niche expansion, reversed size dimorphism, sparrowhawk


Published: 2021-11-27 18:18

Last Updated: 2021-11-30 08:32

Older Versions

CC-By Attribution-NonCommercial-NoDerivatives 4.0 International

Additional Metadata

Data and Code Availability Statement:
Data available from corresponding author on request.

Add a Comment

You must log in to post a comment.


There are no comments or no comments have been made public for this article.