|The pair of wood owls that set me thinking. Arusha, Jan 12|
|Baby Spotted Eagle Owl also in our friend's garden|
So how about this? Raptors need to tear food up to feed young, which is hard work. The females do more tearing to feed the chicks than the males, so they should be bigger. Maybe, but what about raptors (and owls in particular) that mainly eat beetles? And where people have looked at it, there's little evidence of clear sex differences in ripping behaviour anyway.
|Adult Spotted Eagle Owl. Male? It was smaller than the chick.|
There are plenty of other ideas out there (reviewed here), but you can try and make your own up too - I think there's plenty of scope for new ideas in this area, especially if they can actually generate hypotheses which might be testable. At least it will give you something to think about next time you see a pair of raptors...
Wheeler, P., & Greenwood, P. (1983). The Evolution of Reversed Sexual Dimorphism in Birds of Prey Oikos, 40 (1) DOI: 10.2307/3544210
Helmut C. Mueller (1986). The Evolution of Reversed Sexual Dimorphism in Owls: An Empirical Analysis of Possible Selective Factors The Wilson Bulletin, 387-406
ANDERSSON, M., & NORBERG, R. (1981). Evolution of reversed sexual size dimorphism and role partitioning among predatory birds, with a size scaling of flight performance Biological Journal of the Linnean Society, 15 (2), 105-130 DOI: 10.1111/j.1095-8312.1981.tb00752.x