634 NIDIFICATION 



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 KATIT^E, 

 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 Limicolse for 

 instance, the GODWITS (Limosa), the PHALAROPES (Phalaropus), and 

 the DOTTEREL (Eudromias 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, 1 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, 2 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 (Ibis, 

 1891, pp. 52-93 ; and 1892, pp. 55-58). 



2 This seems 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. 



