Tawny owl reproductive biology

Patrik Karell, Jon E. Brommer

At present, this project focuses on tawny owl colour polymorphism. Colour polymorphism is, among birds, most common in owls (33% of species). Such polymorphism often relates to variation in melanism across morphs (light to dark morphs). Polymorphism can be related to differences in individual performance.
Tawny owls are highly polymorphic, varying in their degree of reddish-brown pigmentation (phaeomelanins) deposited in their plumage.

These morphs occur in all populations across Europe. Furthermore, tawny owl plumage colour is highly heritable. Interestingly, colour is under selection in the study population, since the grey morph has, in both sexes, a higher lifetime reproductive success due to grey morphs surviving better than brown morphs (Brommer et al. 2005, PRSB). Although colour is heritable and under selection, colour morph frequencies have remained unchanged over the last 2 decennia.
This project opens an exciting potential window on the genetic base of evolution by combining long-term data, and includes the possibility to also involve molecular techniques. The general aim is to:

• Understand why selection on heritable plumage colouration has not led to colour monomorphy. We are especially working on the genetics of colouration and on understanding whether selection is also in the same direction in other populations.
• Study proximate causes for the observed survival selection on colour. Evidence is suggesting that the brown morph suffers increased mortality under adverse winter conditions. In particular, we are exploring whether blood parasites (avian malaria) are involved in reducing the fitness of the brown morph.

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