In article , Sue & Bob Hobden
writes

Judith, you don't say which type of bird is roosting there, but it may be
Wrens as they are known to roost in quite large numbers in old nests. It
appears one nest in a region seems to be favoured so you can get rather a
lot in a small nest which aids their keeping warm these cold nights.
There are other birds that do the same to keep warm I believe.
Please don't remove the nest until it's no longer needed, possibly April!

We have about a dozen house martin's nests in the eaves. These are used
regularly by wrens and sparrows for roosts in the autumn and winter -
one year a kestrel used one - how it fit in I don't know but it was
definitely a kestrel!! In fact they are even used as nests in spring for
a first clutch - the house martins take over once they come back. You
can buy prefabricated house martin nests from RSPB shops. Why don't you
attach a few to the eaves of your house in places under which you don't
mind guano accumulating?
Sorry, I mean that for Judith, not you Sue/Bob!!!
--
Jane Ransom in Lancaster.
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