01-04-2020

Research by our group shows how bird populations can undergo morphological changes that move them away from their phenotypic optimum, a phenomenon that helps to understand the ecological constraints that condition their adaptability in the face of global change.

The study, published in The Auk: Ornithological Advances, analyses 20 years of ringing data from two populations of common nightingales in the central Iberian Peninsula. We found that nightingales have been shortening their wing length for their body size over this period, even though long-winged individuals are more likely to return from their first migratory journey. How can this be possible if natural selection is about ‘survival of the fittest’?

The key is that natural selection does not necessarily favour individuals that survive longer, but those that leave more offspring. Short-winged nightingales probably achieve greater breeding success, and therefore compensate for their lower survival by leaving more offspring on average than long-winged nightingales. But having short wings may not by itself improve the birds' reproductive success...

 To explain this, we postulate that in nightingales, short wings could come in the same package as other traits that are favourable in the new environmental conditions, due to what is technically known as genetic correlation. During the period under study, we observed that the delay in spring, accompanied by an accentuation of the summer drought, has been shortening the time available for the reproduction of these birds in central Iberia, which could be favouring individuals with moderate reproductive investments. Selection in favour of a smaller clutch size could lead to a reduction in the mean wing length of the population as a collateral effect.

By reducing survival during migrations, short wings are harming rather than helping adaptation to climate change, so the morphological change experienced by nightingales is clearly maladaptive. It is important to be aware of such phenomena if we are to fully understand how bird populations adapt to new environments and help them cope with the challenges of a changing world.

This study would not have been possible without the efforts of many volunteers from the SEO-Monticola Ornithological Group, who have collaborated over the years at their constant effort ringing stations for the long-term monitoring of bird populations.

Further reading:

Original article:

Pérez-Rodríguez, A., Ramírez, Á., Richardson, D. S. & Pérez-Tris, J. 2013. Evolution of parasite island syndromes without long-term host population isolation: parasite dynamics in Macaronesian blackcaps Sylvia atricapilla. Global Ecology and Biogeography. https://doi.org/10.1111/geb.12084