634 NIDIFICA TION 
driven from its home might thrive through the fostering of its 
young by the invader, and thus the abandonment of domestic duties 
would become a direct gain to the evicted householder; so the 
bird which, through inadvertence or any other cause adopted the 
habit of casually dropping her eggs in a neighbour’s nest, might 
thereby ensure a profitable inheritance for endless generations of 
her offspring. ‘This much granted, all the rest will follow easily 
enough, but it must be confessed that this is only a presumption, 
though a presumption which seems plausible if not likely. 
Incubation is performed, as is well known, by the female of nearly 
all Birds, but with most of the Passeres and many others the male 
seems to share her tedious duties, and among the RartIrTé, 
apparently without exception, the cock ordinarily takes that office on 
himself. There are a few groups or perhaps species in which the 
same practice is suspected to obtain—certain of the Limicolx for 
instance, the Gopwits (Limosa), the PHALAROPES (Phalaropus), and 
the DorrerEL (Hudromias morinellus)—and in these it is to be 
remarked that the hen is larger and more brightly coloured than 
her mate. Owing to the unfortunate neglect of those who have 
the best opportunities of making the needful observations,! the 
period of incubation has been ascertained in comparatively few 
birds, and it is here possible to deal with that subject only in the 
most vague and general language. It may be asserted that most of 
the smaller Passeres of Europe hatch their young in from 13 to 
15 days, but in a few species the term is believed to be shortened 
to 10 or 11 days, while in the largest of that Order, the Raven, 
it may be lengthened to some 18 or 19 days. The Barndoor- 
fowl ordinarily takes 21 days, but the Pheasant, though so 
very nearly allied, takes two or three days longer. Most Water- 
birds, so far as is known, and the smaller Birds-of-Prey seem 
to require as long a time, but the TUBINARES are said (Ibis, 
1892, p. 581) to take 35 days, while the Gannet needs at least 
39; and in the Swan incubation lasts from 35 to 40 days, and 
in the Condor, according to Broderip (Notebook of a Naturalist, 
p. 14), 54 days. The temperature of the air is commonly credited 
with having something to do either in hastening or retarding 
exclusion from the egg, but to what extent, or even whether 
justly so or not, seems in the absence of precise experiments 
to be doubtful. Certain birds occasionally begin brooding so soon 
as the first egg is laid,? and this practice unquestionably has its 
advantages, since the offspring being of different ages thereby 
become less of a burthen on the parents which have to minister 
1 The most valuable papers on the subject are by Mr. William Evans (Jbis, 
1891, pp. 52-93; and 1892, pp. 55-58). 
2 This scems to be very often the case with the Owls; but, if my observation 
is not mistaken, the habit is not constant even with the same individual bird. 
