Birds Of Many Kinds Are Extremely Abundant On The Undulating,
Grassy Plains Around Maldonado.
There are several
species of a family allied in structure and manners to our
Starling:
One of these (Molothrus niger) is remarkable from
its habits. Several may often be seen standing together on
the back of a cow or horse; and while perched on a hedge,
pluming themselves in the sun, they sometimes attempt to
sing, or rather to hiss; the noise being very peculiar,
resembling that of bubbles of air passing rapidly from a small
orifice under water, so as to produce an acute sound. According
to Azara, this bird, like the cuckoo, deposits its eggs
in other birds' nests. I was several times told by the country
people that there certainly is some bird having this
habit; and my assistant in collecting, who is a very accurate
person, found a nest of the sparrow of this country (Zonotrichia
matutina), with one egg in it larger than the others,
and of a different colour and shape. In North America
there is another species of Molothrus (M. pecoris), which
has a similar cuckoo-like habit, and which is most closely
allied in every respect to the species from the Plata, even in
such trifling peculiarities as standing on the backs of cattle;
it differs only in being a little smaller, and in its plumage
and eggs being of a slightly different shade of colour. This
close agreement in structure and habits, in representative
species coming from opposite quarters of a great continent,
always strikes one as interesting, though of common
occurrence.
Mr. Swainson has well remarked, [8] that with the exception
of the Molothrus pecoris, to which must be added the
M. niger, the cuckoos are the only birds which can be called
truly parasitical; namely, such as "fasten themselves, as it
were, on another living animal, whose animal heat brings
their young into life, whose food they live upon, and whose
death would cause theirs during the period of infancy." It
is remarkable that some of the species, but not all, both of
the Cuckoo and Molothrus, should agree in this one strange
habit of their parasitical propagation, whilst opposed to each
other in almost every other habit: the molothrus, like our
starling, is eminently sociable, and lives on the open plains
without art or disguise: the cuckoo, as every one knows,
is a singularly shy bird; it frequents the most retired thickets,
and feeds on fruit and caterpillars. In structure also
these two genera are widely removed from each other.
Many theories, even phrenological theories, have been advanced
to explain the origin of the cuckoo laying its eggs in
other birds' nests. M. Prevost alone, I think, has thrown
light by his observations [9] on this puzzle: he finds that the
female cuckoo, which, according to most observers, lays at
least from four to six eggs, must pair with the male each time
after laying only one or two eggs. Now, if the cuckoo was
obliged to sit on her own eggs, she would either have to sit
on all together, and therefore leave those first laid so long,
that they probably would become addled; or she would have
to hatch separately each egg, or two eggs, as soon as laid:
but as the cuckoo stays a shorter time in this country than
any other migratory bird, she certainly would not have time
enough for the successive hatchings.
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