MIGRATION 553 
affording the sole or the most convenient site for the nest in the 
neighbourhood, but in so many instances such is not the case that 
we are led to believe in the existence of a real partiality, while 
there are quite enough exceptions to shew that a choice is frequently 
exercised. ‘The same may equally be said of the most migrant of 
Birds, and perhaps the strongest instance that has ever come to the 
knowledge of the writer refers to one of the latter. A pair of 
Stone-CURLEWS ((Zidicnemus crepitans)—a very migratory species, 
affecting almost exclusively the most open country—were in the 
habit of breeding for many years on the same spot! though its 
character had undergone a complete change. It had been part of 
an extensive and barren rabbit-warren, and was become the centre 
of a large and flourishing plantation. 
With these two sets of facts before us we may begin to try and 
account for the cause or causes of Migration. In some cases want 
of food would seem to be enough, as it is undoubtedly the most 
obvious cause that presents itself to our mind.2 The need which 
all animals have of finding for themselves proper and _ sufficient 
sustenance is all-powerful, and the difficulties they have to encounter 
in obtaining it are so great that none can wonder that those which 
possess the power of removing themselves from a place of scarcity 
should avail themselves of it, while it is unquestionable that no 
Class of animals has this facility in a greater degree than Birds.? 
Even among many of those species which we commonly speak of 
as sedentary, it is only the adults which maintain their ground 
as one of the most southern points whence the midnight sun may be seen—is 
mentioned by the French astronomer Maupertuis as having been observed by 
him in the year 1736. In 1799 the nest was rediscovered by Skjoldebrand and 
Acerbi. In 1853 Wolley found it tenanted, and from enquiries he made of the 
neighbours it was evident that such had yearly been the case so far as any one 
could remember, and so it was in 1855 as I myself can testify. In 1779 accord- 
ing to one account, in 1785 according to another, a pair of the Blue Titmouse 
(Parus ceruleus) built their nest in a large earthenware bottle placed in the 
branches of a tree in a garden at Oxbridge near Stockton-on-Tees. With two 
exceptions only, this bottle, or a second which had been placed close to it, was 
tenanted by a pair of birds of this species from the year in which it was first 
occupied until 1878, when I saw it (see Yarrell’s British Birds, ed. 4, i. pp. 
58, 486) ; but I regret to add that I learnt through Canon Tristram in 1892 that 
the occupancy had ceased for four years. 
1 At Elveden in Suffolk. 
2 Far more so than variation of the temperature, though in popular belief 
that probably holds the first place. But Birds generally, as compared with other 
Vertebrates, are but slightly affected by extremes of heat or cold, and indeed 
(so far as we can judge) by most climatic influences, provided only their supply 
of food is not affected thereby (¢f Max Schmidt, Zoolog. Garten, 1865, pp. 
330-340). 
3 The only animals which approach Birds in the extent and character of their 
migrations are Fishes, of which there is no need here to say anything. 
