If you are getting high numbers of dead birds in the garden, you could seek advice from DEFRA.
The telephone number for England and Wales is : 08459 335577.
We are seeing many dead and dieing woodpigeons on Son's estate, the old timers blame 'beech mast disease' (whatever that is) that comes from eating too much mast.
If you can't get through to the help-line, then maybe they will respond to an email.
Hope you don't get anymore dead birds, I'm quickly running out of food on these frosty mornings!