Sunday, 20 January 2013

Winter feeding and fattening

The latest available figures reveal that sixteen HLS agreement holders have adopted the new supplementary feeding option to support farmland birds in the critical late winter period when other sources of food are in short supply.  Some farmers are also adding this option to their ELS agreements.  Given the very short time in which to apply back in December, this is very encouraging and is a classic example of research by the Allerton Project (and colleagues in BTO and RSPB) being translated into practical action on the ground.

The data that we have gathered at Loddington over many years suggest that winter feeding results in more than twice as many songbirds present during the second half of the winter.  More importantly though, our results suggest that breeding bird numbers could also be up by 30%.  More food in late winter means more birds, and better survival of those birds so that more are present in the following spring.

Trail Camera image of yellowhammers feeding at a feeder at Loddington

This encouraging prospect and the current snowy weather have combined to prompt me to dig out some data from several years ago when I first got interested in this issue and started catching yellowhammers through the winter to see how much fat they were carrying.  Birds lay down more fat as the winter progresses - insurance against uncertainty associated with cold weather, shorter days, snow cover and depleted food reserves.  In late winter, fat levels decline and birds become more vulnerable to starvation.

Yellowhammer body condition index, reflecting fat reserves (1995/96 data).

I also have some results for the same period from the Rybachy bird ringing station on the eastern shore of the Baltic.  Fat reserves in yellowhammers are very different here, and considerably higher in the autumn than they are for British birds.  The reason is that Russian birds are laying down fat to fuel a southward migration, rather than to survive the winter on the same site.  There are no data for the winter because the birds have gone!

The low fat levels in the British birds in March serve to highlight the need for supplementary feeding in the scond half of the winter, but especially at the end of the winter when the food supply is at its lowest.  But these data are also a reminder that the same species can behave differently in different countries.

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