164 On the Duration of the Period of Incubation.


summer, was accelerated ; and took place after nineteen days.

The Rufous Tinamou (. Rhynchotus rufescens) incubates for twenty-

one days, according to the late Mr. Bartlett.


Taking the larger Parrots and Crows as types of long-

lived birds, we find that the incubation of the former lasts

between three and four weeks, or, allowing a slight margin

because of the difficulty of obtaining exact data in the case of

birds which lay at irregular intervals in holes, we will say three

weeks ; that of the latter about the same period. On the other

hand if we take the Zebra-finch and Silverbills as types of short¬

lived birds (and I have found them distinctly more so than many

other Grass-finches which are less easily bred) we find that their

period of incubation is only eleven days. This certainly looks

as if there were some connection between the two facts.


As aviary birds, whatever they may be when at liberty,

doves are undoubtedly long-lived, and retain their full vitality

for many years ; as is evident from the fact that one of my male

Necklaced-doves, purchased in 1894, is now breeding with a

white Barbary-dove; and my Bronze-winged Pigeons, purchased

in 1897, have spent the past winter in an open out-door aviary;

in the large doves seventeen to nineteen days is a fair average

for the hatching of the young.


The typical Thrushes I believe are not naturally long-

lived birds, so that one might expect their period of incubation

to be short. On the other hand, I think the larger Mynahs live

to a good age ; consequently their eggs should be more slowly

developed.


In Mr. Evans’ papers previously referred to, the following

may be summarized as desiderata in the foregoing account :—

Chats about 14 days; Warblers 11-16 days, but mostly 13-15

days; Wagtails 13-14 days; Swallow 15-16 days; Park 13-14

days; Nuthatch 13-14days ; Tits 14-17 days ; Flycatcher 14 days ;

Zosterops 9-10 days; Creeper 15 days; Crossbill 14-15 days;

Woodpeckers 14-18 days ; Nicobar Pigeon 28 days ; Crows 17-19

days; Kingfishers 14-19 days ; Rollers 18-20 days ; Cockatoos 21

days ; but these papers should be studied carefully in con¬

junction with the present one.



