78 HANDBOOK OF BRITISH INLAND BIRDS 
be finished and used as a nursery. After the young 
Wrens have left the nest it is sometimes used later 
in the summer for roosting purposes at night by 
broods of other small birds ; a kind of small 
bumble-bee, too, will sometimes build its own nest 
inside it. In winter. Wrens will roost in their 
own bower-nests and true nests alike, as well as 
in those of other birds, such as House Martins. 
Like many other creatures, the Wren tends to 
develop differences of structure and colour when 
it is isolated on small and remote islands ; and it 
has been decided that one such variety, that which 
inhabits the distant Hebridean Island of St. Kilda, 
is sufficiently distinct to be given specific rank as 
the St. Kilda Wren. It is open to argument, how- 
ever, whether it really deserves separate recognition 
any more than the Black-bellied Dipper, which we 
discussed on a former page, and many other similar 
varieties. It is larger and darker than Wrens of 
the ordinary description. 
TREE-CREEPER. 
( Certhia familiaris, ) 
Tree-climber. — Like the Nuthatch and Gold- 
crest, this delicate little bird is, perhaps, more 
familiar to most people in winter than in summer, 
when the full foliage helps to conceal it. It is 
