On 29/06/13 11:35, rbel wrote:

Having read the original paper when it was published last week I would
summarise it as an interesting but fairly limited study of one species
in a woodland environment. The focus was primarily on winter feeding
of fat supplements which had an apparent impact on reproductive and
fledgling success.

The possible causes for this were the survival through the winter of
potential parent birds who would not normally make it through to the
reproductive stage - thus poor reproductive success; insufficient
spring/summer food to support increased number of fledglings and
unbalanced diet resulting in imperfect eggs.

Much more likely to be salt residue in the fat.

--
Rusty Hinge