As regular CFZ-watchers will know, for some time Corinna has been doing a column for Animals & Men and a regular segment on On The Track... particularly about out-of-place birds and rare vagrants. There seem to be more and more bird stories from all over the world hitting the news these days so, to make room for them all - and to give them all equal and worthy coverage - she has set up this new blog to cover all things feathery and Fortean.

Tuesday, 13 September 2016

Devotion to rearing chicks can come at a cost for migratory birds

Date: August 30, 2016

Birds that have to work harder during breeding season will feel the effects of their exertions the following year, according to research by Oxford University scientists.

A new study published in the Journal of Animal Ecology found that migratory seabirds suffered negative repercussions when they had to spend more time rearing chicks, including decreased breeding success when they returned to the colony the following spring.

The study artificially altered the length of the chick-rearing period for pairs of Manx shearwaters, giving new insights into the consequences for birds whose reproductive phase doesn't go to plan. All parent pairs involved in the study cared for their foster chicks until they were fully reared -- often at their own expense.

Lead author Dr Annette Fayet, of the Oxford Navigation Group in the University of Oxford's Department of Zoology, said: 'The results of this study provide evidence for carry-over effects on the subsequent migratory, wintering and breeding behaviour of birds.'

Carry-over effects are the processes by which events in one breeding season may affect the outcome of the subsequent season. But the exact nature of these effects, as well as whether they affect other events in birds' annual cycles, such as migration and wintering, has been unclear.

Dr Fayet said: 'Birds that had their chick-rearing period extended in our study delayed the start of their autumn migration and spent less time at the wintering grounds, and while they were there they spent less time resting. When they returned to the colony the following spring, they started breeding later, laid smaller eggs, reared lighter chicks -- early, heavy chicks survive better -- and overall had a lower breeding success.

'This suggests that the birds were in poorer condition after working harder during the experimental breeding season and shows the negative effects on both non-breeding and breeding behaviour in the year following the experiment.'

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