Editor's Choice: Breeding season weather determines long-tailed tit reproductive success

Submitted by Johan on 5 October 2015.

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It is common that avian scientists working with breeding biology claim that weather has a large impact on breeding productivity although this is usually just a “feeling” and seldom formerly tested.

When Gullett et al. did so, making use of a 19-year study of a population of long-tailed tits (Aegithalos caudatus), they astonishingly found that weather during the breeding season did not affect neither clutch size, hatching success nor fledging success. However, weather did have an effect on recruitment but it was not mediated by winter weather, which is the common belief, but by spring temperatures when the young were produced. Gullett et al. found that cold March and warm May temperatures had a positive effect on recruitment. Juvenile survival is probably very dependent on the immediate post-fledging conditions and a cold March would delay the food peak to include this crucial period and a warm May, which is the period of fledging in long-tailed tits, would also be beneficial for survival. This is a really important study telling us that it is so easy to believe things but when actually tested, taking density-dependence and predation rates into account, it proves to be quite different from our beliefs.

Jan-Åke Nilsson, Editor in Chief

You can read the paper for free here: http://onlinelibrary.wiley.com/doi/10.1111/jav.00560/full

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