On the Duratioi of the Period of Incubation. 151


THE DURATION OF THE PERIOD OF INCUBATION.


By Arthur G. Butter, Ph.D., F.L.S., F.Z.S., etc.


The study of this branch of ornithology has, hitherto,

hardly been touched in the various faunistic works in which the

life-histories of birds have appeared: in the United States alone

does any serious effort seem to have been made to put on record

the various periods for which the birds of that country incubate.*

In the British Isles, excepting perhaps in the case of Game-

birds, and others which are conspicuously brought under man’s

notice by domestication or other causes, next to nothing appears

to be known of this important item of avian life.f


Of course the explanation of this apparent neglect, in a

country which has amassed some of the finest collections of eggs

in the world, is evident enough: an ardent collector of eggs or

nests naturally secures his prizes while they are fresh, putting

off the study of the duration of incubation to a more convenient

season ; and having secured the clutches of a species which he

requires, promptly forgets all about the unknown, and therefore

more interesting, item.


If only to discover whether the longevity of birds bears a

similar relation to the period of incubation, to that which the

longevity of mammals appears to bear to the period of gestation,

the study of this part of their life is of interest; but it must

also be remembered, that no man who neglects a single detail,

can claim to have a thorough knowledge of the nidification of

any one species. To the aviculturist, who desires to be prepared

for the hatching of his broods, it is of considerable importance to

know when to expect this event.


In order to induce aviculturists and others interested in



* See Charles Beudire’s “Life Histories of North American Birds.”


+ After the present paper had gone to press Mr. Charles Chubb of the Nat. Hist.

Museum, who is a perfect walking Encyclopedia of Ornithological literature, called my

attention to two important papers on this subject, which I had unfortunately overlooked,

by Mr. William Evans, F.R.S.E., in *' The Ibis” for 1891, pp. 52-93 and 1892, pp. 56-58.

They are most interesting as filling up many of the gaps in the present paper with respect

to British birds. Many of the results have been obtained by the use of an incubator; and

although great care has been taken to ascertain the correct temperature suitable for hatch¬

ing the eggs, it may be anticipated that some of them will need revision. I11 some in¬

stances also where the duration of incubation had been counted from the laying of the

first egg the statement of the observers will have (as Mr. Evans points out) to be accepted

with reservations.



