Islands
as the Common Tern, and is, as far as I can make out, only an occasional
autumnal visitant, and then young birds of the year most frequently
occur, as I have never seen a Guernsey specimen of an adult bird. I do
not think it ever visits the Islands during the spring migration; I did
not see one about the Vale in the summer of 1878, nor did Mr. Howard
Saunders and myself recognise one when we visited the rocks to the north
of Herm. It may, however, have occurred more frequently than is
supposed, and been mistaken for the Common Tern, so it may be as well
to point out the chief distinctions: these are the short tarsus of the
Arctic Tern, which only measures 0.55 of an inch, whilst that of the
Common Tern measures 0.7 of an inch; and the dark grey next to the shaft
on the inner web of the primary quills of the Arctic Tern, which is much
narrower than in those of the Common Tern. These two distinctions hold
good at all ages and in all states of plumage; as to fully adult birds
in breeding plumage there are other distinctions, the tail of the Arctic
Tern being much longer in proportion to the wing than in the Common
Tern, and the bill being nearly all red instead of tipped with
horn-colour.

The Arctic Tern is not included in Professor Ansted's list, and there is
no specimen at present in the Museum.

165. BLACK TERN. _Hydrochelidon nigra_, Linnaeus. French, "Guifette
noire," "Hirondelle de mer epouvantail."[32]--The Black Tern is by no
means a common visitant to the Islands, and only makes its appearance in
the autumn, and then the generality of those that occur are young birds
of the year. I have one specimen of a young bird killed at the Vrangue
on the 1st October, 1876. It does not seem to occur at all on the spring
migration; at least I have never heard of or seen a Channel Island
specimen killed at that time of year. As this is a marsh-breeding Tern,
it is not at all to be wondered at that it does not, at all events at
present, remain to breed in the Islands, there being so few places
suited to it, though it is possible that before the Braye du Valle was
drained, and large salt marshes were in existence in that part of the
Island, the Black Tern may have bred there. I can, however, find no
direct evidence of its having done so, and therefore can look upon it as
nothing but an occasional autumnal straggler.

The Black Tern is not included in Professor Ansted's list, and there is
no specimen in the Museum. T