batbox problems

BLUE TITS NESTING IN BAT BOXES
by George Yates & John Matthews

(We would like to thank British Birds May ’98 for permission to reproduce this article)

As licensed bird-ringers and bat-workers, we organise nestbox schemes for birds and bats. On 15^th July 1993 while examining a standard batbox, we found a dead brood of 6 almost fully-fledged Blue Tits Parus caeruleus. It would appear that the adult tits had entered the box through the slot at the bottom, built a nest and hatched young. As the young approached fledging age their trampling had flattened the nest across the entrance slot and, just before fledging, the nest had completely blocked the entrance, preventing the adults from entering. The young were trapped inside and subsequently starved to death.

Reflecting on this incident prompted us to examine, on 7^th November 1993, a further 5 standard type batboxes attached to isolated Pedunculate Oaks Querus robur in a 30 year old plantation of Scots Pine Pinus sylvestris. Three of these contained old nests, presumably of Blue Tits, of which, two appeared (from the appearance of feather scale) to have been successful whilst the third contained an incomplete nest. These batboxes could represent a common hazard for Tits that use them. We suggest two remedies:

In all batboxes, bore a 25mm hole in the position of the conventional nestbox hole but close this with a keyhole-type cover (Figure 1). Inspect the boxes in April and, if birds are using them, remove the hole cover to allow access above the nest. After fledging remove the nest, re-cover the access hole, and allow bats to use the box during July to September.

Use the bat boxes (see Figure 2 above) designed by Mick Finnemore (a founder  member of the Warwickshire Bat Group). While these have been used with great success by bats they are of insufficient volume to be attractive to Blue Tits as nesting sites.