Fat provisioning in winter impairs egg production during the following spring: a landscape-scale study of blue tits

Author(s): Plummer, K.E., Bearhop, S., Leech, D.I., Chamberlain, D.E. & Blount, J.D.

Published: January 2013  

Journal: Journal of Animal Ecology Volume: 82 ( part 3 )

Digital Identifier No. (DOI): 10.1111/1365-2656.12025

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Although many of us provide food for garden birds, especially in winter, we are still only in the early stages of understanding exactly how this affects wild bird populations.  One possibility is that winter food enhances birds’ ability to invest in future reproduction.  However, it is likely that the type of nutrients a bird receives from supplementary food will be an important factor in determining whether this is the case. A new study by scientists at the University of Exeter, in collaboration with the BTO and the University of Turin, has shown exactly that. 

In a three year study of woodland Blue Tit populations, researchers examined the consequences of providing different winter food supplements for egg production.  Their results showed that provisioning with fat alone resulted in smaller relative yolk mass, and reduced yolk carotenoid concentrations in early breeders.  This suggests that females which utilised a fat-rich diet in winter were less able to acquire some of the important resources needed to form yolk during egg production.  However, the addition of vitamin E to the fat mitigated the negative effects of a fat-rich diet.  It is thought that this may be because, as an antioxidant, vitamin E provides protection against oxidative damage which could result from increased metabolism after eating fatty foods. 

These findings suggest that birds require a balanced diet, much like we do, to aid their reproduction, and it underlines the importance of considering the nutritional value of provisioned foods.  This study highlights that much more research is needed to fully understand the impacts of winter feeding, in particular how it affects individual survival.


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