142 HABLTS OF BIRDS, 
the same is incomplete; yet, on the supposition 
that it is not the same, but successive pairs, which 
are observed in the same place, we are led to the 
curious inquiry how the death or disappearance of 
one pair is supplied by another. We have in more 
than one instance observed a pair of magpies nestle 
on the same tree for a series of years, where they 
reared a brood of four or five young ones every 
season. All of these disappeared from the neigh- 
bourhood; at least, we observed no increase in the 
number of nests. In one instance we observed a 
magpie’s nest thus successively occupied for ten 
years. 
The continuance of a nest in the same spot for 
several years is more remarkable in the case of 
migratory birds than in that of magpies, which do 
not migrate, and seldom go to any considerable 
distance from their breeding trees. There has been, 
in a garden adjacent to ours, the nest of a black-cap 
(Sylvia atricapilla) for a succession of years, and 
broods have been successively reared there, with- 
out any observable increase in the population of the 
species. Yet this bird, which is little bigger than a 
wren, weighing only half an ounce, has to traverse 
annually the whole of the south of Europe, and 
probably a great proportion of the north of Africa, 
exposed, of course, to numerous accidents, as well 
as to occasional scarcity of its appropriate food. 
From the regular annual restoration, however, of 
this nest at the same spot, it is obvious that one, if 
not both of the black. caps, must have been wont to 
perform this extensive migration to and from Af- 
rica as safely as the more hardy cuckoo or the 
more swift-winged swallow. During the spring of 
1831, the back-caps, which we suppose to be the 
same birds, from their keeping to the same place 
of nestling, were more than usually late in arri- 
ving; for in another garden about a mile off there 
were young in the hereditary nest of black-caps 
