"Ve 
131 
was suckling these young ones fed most sparingly, and rarely took 
any drink. From the before-mentioned observations we may infer 
that the period of gestation of the Bears is about seven months. 
3. NoTE ON THE SUPPOSED OCCURRENCE OF THE HiIRUNDO 
BICOLOR OF NortTH AMERICA IN ENGLAND. By ALFRED 
Newron, M.A., F.Z.S., &e. 
I venture to send for exhibition a skin of the North American 
Hirundo bicolor of Vieillot, which was formerly the property of my 
late very good friend Mr. John Wolley, and which there can be little 
doubt was obtained from a bird killed in this country, though Mr. 
Wolley, with that admirable caution which distinguished him in re- 
cording the reported occurrence (‘Zoologist,’ 1853, p. 3806), was 
careful to mention that there was “a possibility of mistake’ in the 
matter. 
I think that perhaps some members of the Society will view this 
specimen with a certain amount of interest ; but, apart from this, my 
object in its exhibition is mainly to draw the attention of naturalists 
to a matter which is every day becoming of greater consequence to 
those ornithologists who chiefly occupy themselves with the Avi- 
fauna of any one district. I refer to the occurrence within parti- 
cular limits of strong examples of exotic species. It is not only 
“British bird” students who find in these alien immigrants a great 
cause of perplexity. To whatever country we go, we are, perhaps 
before we have well ascertained the number of the bond fide species, 
puzzled by some wanderer turning up exactly where he was least 
wanted. In my own opinion, the ornithologist must accept his 
position with all its responsibilities ; he chooses to study a class of 
beings, some of whom, for all sublunary purposes at least, are blest 
with almost infinite powers of locomotion. He must, therefore, not 
complain if in the course of a morning’s walk here in England, an 
Australian Swift flies in his face, or he picks up a dead Crossbill of a 
Transatlantic species ; and he must invoke no Deus ex machina in the 
shape of an auxiliary-screw clipper or a careless aviary-keeper to 
account for the incident. Facts like these hardly admit of a doubt, 
and force themselves day by day more and more upon the notice of 
the thoughtful naturalist. For some time, indeed, European orni- 
thologists have been accustomed to regard the properly authenticated 
appearance of an exotic species, which there may be good reason to 
suppose have reached our shores without intentional human aid, 
as sufficient ground for including it in the list of our birds. But as 
observers have of late so largely increased, so have these occurrences 
been more frequently noticed ; and it seems absolutely necessary to 
prescribe some limit to prevent our really native species from being 
outnumbered by these foreigners. The difficulty is to know where 
to draw the line; and to this point I would invite the careful con- 
sideration of naturalists, It may be all very well to ‘call Thalassi- 
