a) 
48 BRITISH BIRDS. [von. x1. 
of the clutch which showed itself porous to any marked 
extent. It may be remarked that the shells of all birds’ 
eggs are more or less porous, and during the process of in- 
cubation about one-seventh of the total weight of the shell 
and contents (or between 14-15%) is lost through evaporation. 
When the internal membrane is ruptured from any cause, 
the process is of course much more readily apparent. See 
N. H. Foster, Irish Naturalist, X1., p. 287; H.S. Gladstone, 
Ibis, 1904, p. 376, ete.—-F. C. R. JourDAIN. 
INCUBATION-PERIOD OF SpaRROW-Hawxk.—Mr. A. Brook 
states (Field, 14, IV. °17, p. 559) that from his observation 
the incubation-period of Accipiter n. nisus is about twenty- 
eight days. In one case, however, thirty-one days elapsed 
from the laying of the last egg before the first young one 
hatched. This is a considerably shorter period than that 
recorded by other observers. Mr. 8. E. Brock estimates it as 
30-32 days. Messrs. E. W. H. Blagg, J. H. Owen and the 
Rev. F.C. R. Jourdain at 35 days, while in a nest watched 
by Prof. J. H. Salter the period lasted 37-38 days. 
PALE AND DARK-BREASTED BRENT GEESE.—Considerable 
discussion, initiated by Miss E. V. Baxter and Miss L. J. 
Rintoul, has taken place in The Scottish Naturalist recently 
concerning these two forms of the Brent Goose. In quoting 
our Hand-List the authors mentioned have omitted to note 
that in our first list of “‘ corrections and additions ” (Brit. B. 
IX., p. 7) we stated that the two forms, which we had in the 
Hand-Iist considered as distinct sub-species, were apparently 
merely individual varieties, since they are now known to nest 
together in the Old World. We take this opportunity of 
stating more positively that No. 283 Branta bernicla bernicla 
and No. 284 Branta bernicla glaucogastra of our Hand-List are 
dimorphisms of one species and should both be called Branta 
bernicla bernicla. 
RED-NECKED GREBES IN Moray AREA.—Miss A. C. 
Jackson records (Scot. Nat., 1917, p. 69) having satis- 
factorily identified two Podiceps g. griseigena in a northern 
firth on November 30th, 1916, and Mr. C. Oldham states 
(l.c., p. 117) that he saw several birds of this species in 
Cromarty Firth on October 9th, 1912. Miss Jackson states 
that the species has not, hitherto, been recorded for the 
Moray area. 
Great SxKvuA In Surrork.—Mr. W. H. Tuck states 
(Trans. Norf. Norwich Nat. Soc., Vol. X., Part 2, p. 178) 
that an example of Stercorarius s. skua occurred near Ixworth, 
forty miles inland, in January, 1915. 
