My Studio Neighbors | Page 9

young bird in the grass near
my door, and, on approaching, discovered the spectacle of a cow-bird,
almost full-fledged, being fed by its foster-mother, a chippy not more
than half its size, and which was obliged to stand on tiptoe to cram the
gullet of the parasite.
The victims of the cow-bird are usually, as in this instance, birds of
much smaller size, the fly-catchers, the sparrows, warblers, and vireos,
though she occasionally imposes on larger species, such as the orioles
and the thrushes. The following are among its most frequent dupes,
given somewhat in the order of the bird's apparent choice:
song-sparrow, field-sparrow, yellow warbler, chipping-sparrow, other
sparrows, Maryland yellow-throat, yellow-breasted chat, vireos,
worm-eating warbler, indigo-bird, least-flycatcher, bluebird, Acadian
flycatcher, Canada flycatcher, oven-bird, king-bird, cat-bird, phoebe,
Wilson's thrush, chewink, and wood-thrush.
But one egg is usually deposited in a single nest; the presence of two
eggs probably indicates, as in the case of the European cuckoo, the
visits of two cow-birds rather than a second visit from the same
individual--the presence of two cow-bird chicks of equal size being
rather a proof of this than otherwise, in that kind Nature would seem to
have accommodated the bird with an exceptional physiological
resource, which matures its eggs at intervals of three or more days, as
against the daily oviposition of its dupes, thus giving it plenty of time
to make its search and take its pick among the bird-homes. Whether the
process of evolution has similarly equipped our cow-bird I am not

aware; but the vicious habits of the two birds are so identical that the
same accommodating functional conditions might reasonably be
expected. It is, indeed, an interesting fact well known to ornithologists
that our own American cuckoos, both the yellow-billed and
black-billed, although rudimentary nest-builders, still retain the same
exceptional interval in their egg-laying as do their foreign namesake.
The eggs are laid from four days to a week apart, instead of daily, as
with most birds, their period of perilous nidification on that haphazard
apology of a nest being thus possibly prolonged to six weeks. Thus we
find, in consequence, the anomalous spectacle of the egg and
full-grown chick, and perhaps one or two fledglings of intermediate
stages of growth, scattered about at once, helter-skelter, in the same
nest. Only two years ago I discovered such a nest not a hundred feet
from my house, containing one chick about two days old, another
almost full-fledged, while a fresh-broken egg lay upon the ground
beneath. Such a household condition would seem rather demoralizing
to the cares of incubation, and doubtless the addled or ousted egg is a
frequent episode in our cuckoo's experience.
It is an interesting question which the contrast of the American and
European cuckoo thus presents. Is the American species a degenerate or
a progressive nest-builder? Has she advanced in process of evolution
from a parasitical progenitor building no nest, or is the bird gradually
retrograding to the evil ways of her notorious namesake?
The evidence of this generic physiological peculiarity in the intervals of
oviposition, taken in consideration with the fact of the rudimentary nest,
would seem to indicate the retention of a now useless physiological
function, and that the bird is thus a reformer who has repudiated the
example of her ancestors, and has henceforth determined to look after
her own babes.
With the original presumed object of this remarkable prolonged
interval in egg-laying now removed, the period will doubtless be
reduced through gradual evolution to accommodate itself to the newly
adopted conditions. The week's interval, taken in connection with the
makeshift nest or platform of sticks, is now a disastrous element in the

life of the bird. Such of the cuckoos, therefore, as build the more
perfect nests, or lay at shortest intervals, will have a distinct advantage
over their less provident fellows, and the law of heredity will thus
insure the continual survival of the fittest.
The cuckoo is not alone among British birds in its intrusion on other
nests. Many other species are occasionally addicted to the same
practice, though such acts are apparently accidental rather than
deliberate, so far as parasitical intent is concerned. The lapse is
especially noticeable among such birds as build in hollow trees and
boxes, as the woodpeckers and wagtails. Thus the English starling will
occasionally impose upon and dispossess the green woodpecker. In the
process of nature in such cases the stronger of the two birds would
retain the nest, and thus assume the duties of foster-parent. Starting
from this reasonable premise concerning the prehistoric cuckoo, it is
not difficult to see how natural selection, working through ages of
evolution by heredity, might have developed the habitual resignation of
the evicted bird, perhaps to the ultimate entire abandonment of the
function of incubation. Inasmuch as "we