Tawny Owls Strix aluco from a southern European population differ in size and degree of reverse sexual dimorphism from northern European counterparts

ABSTRACT

Tawny Owls in southern Europe were trapped and measured. Compared to males, the females were larger, heavier, and more greyish in colour, but there was a large biometric overlap. The variable with the highest Storer’s dimorphism index (SDI) was weight, though our population had one of the smallest dimorphisms observed in Europe for weight. It has been proposed that differences in diet could lead to differing behaviour and, in consequence, the observed dimorphism degree (SDI) by natural selection.

KEYWORDS:

• RSD
• Bergmann
• Storer’s dimorphism index
• diet
• biometrics
• latitude

Acknowledgements

The Administrations from Bizkaia Gipuzkoa and Burgos authorised the ringing activity. N. Pagaldai was supported by a Basque Government predoctoral fellowship grant (PRE_2018_1_0004). We also want to thank all of the people who helped with the fieldwork.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by Eusko Jaurlaritza [grant number PRE_2018_1_0004].