390 THE ZOOLOGIST. 
period of the year (spring) Rooks pass over the little island of 
Heligoland at a much greater altitude than this, according to 
Gatke. They must therefore mount after leaving Norfolk, and 
it is probably done gradually. Often, he says, only their calls, 
faintly audible from above, give indication that they are speed- 
ing on their way above the range of human vision (cf. ‘‘ Birds 
of Heligoland,” p. 207). When I was in Heligoland in 1883 I 
had the chance of conversing with the veteran observer about 
migration, a subject on which he knew more than any man 
living. Gitke has a great deal to tell his readers in his 
admirable book about the Grey Crow and the Rook—witness the 
many references to the former in the index. He tells us that 
the number of Grey Crows which pass that island of the North 
Sea in spring is scarcely half of what pass it in autumn. This 
he accounts for by supposing that most of them take a shorter 
route on their return journey (T. C. p. 43), but I think it likely 
that wind has something to do with it, and one must make 
allowance for a considerable annual waste of life, which in all 
probability takes place. 
During the present spring (1912) the exodus has been 
observed as usual on the coast of Norfolk, where it commenced 
early this year. The following are some notes made by an 
observer who is situated about a mile from the sea :— 
February 21st.—Grey Crows, Rooks, and Jackdaws, passing 
over Northrepps in a south-easterly direction—the wind being 
light from the west—from 7.45 a.m. to 11.30 a.m. 
23rd.—More Grey Crows flying in the same direction. Wind 
the same. 
24th.—More Grey Crows, Rooks, and Jackdaws, passing 
over. No wind. 
March 18th.—Grey Crows passing over Northrepps and 
Overstrand from 6.25 a.m. to 2.15 p.m. A gentle wind from 
the south. 
19th.—Grey Crows passing over from 6.20 a.m. to 12.30 p.m. 
Hardly any wind. 
Having enquired of Mr. Hugo Weigold, who carries on 
Gatke’s work, how these dates fitted in with his observations 
made at the Biological Institute at Heligoland, he replied as 
follows :— 
