: Argentine Ornithology, Volume I (of 2) by P. L Sclater, W. H Hudson (books to read in your 20s female .txt) 📖

27 inches deep, and 16 or 18 in circumference, and appears now

nearly finished. I am sure that this nest will be attacked before long,

and I have resolved to watch it closely.

 

September 28.--To-day I saw a Bay-wing (_M. badius_) on the nest; it

climbed over it, deliberately inspecting every part with the critical

air of a proprietor who had ordered its construction, taking up and

rearranging some sticks and throwing others away from the nest. While

thus engaged, two common Cow-birds (_M. bonariensis_), male and female,

came to the tree; the female dropped on to the nest, and began also to

examine it, peering curiously into the entrance and quarrelling with the

first bird. After a few minutes she flew away, followed by her glossy

consort. The Bay-wing continued its strange futile work until the owners

of the nest appeared, whereupon it hopped aside in its usual slow

leisurely manner, sang for a few moments, then flew away. The similarity

in the behaviour of the two birds struck me very forcibly; in the great

interest they take in the nests of other birds, especially in

large covered nests, the two species are identical. But when the

breeding-season comes their habits begin to diverge: then the Common

Cow-bird lays in nests of other species, abandoning its eggs to their

care; while the Bay-wings usually seize on the nests of other birds

and rear their own young. Yet, as they do occasionally build a neat

elaborate nest for themselves, the habit of taking possession of the

nests of other birds is, most likely, a recently acquired one, and

probably its tendency is to eradicate the original building instinct.

 

October 8.--This morning, while reading under a tree, my attention was

aroused by a shrill note, as of a bird in distress, issuing from the

neighbourhood of the Leñatero's nest; after hearing it repeated at

intervals for over twenty minutes, I went to ascertain the cause. Two

Bay-wings flew up from the ground under the nest, and on searching

in the rank clover growing under the tree, I discovered the female

Leñatero, with plumage wet and draggled, trembling and appearing half

dead with the rough treatment she had experienced. I put her in the

sun, and after half an hour, hearing her mate calling, she managed to

flutter feebly away to join him. The persecutors had dragged her out

of the nest, and would, no doubt, have killed her, had I not come so

opportunely to the rescue.

 

Since writing the above, I have continued to watch the nest. Both the

Bay-wings and Leñateros left it for some days. Six days after picking up

the ill-treated female, the Leñateros came back and resumed possession.

Four days later the Bay-wings also came back; but on finding the

nest still occupied, they took possession of an unfinished oven of

an Oven-bird on another tree within twenty yards of the first, and

immediately began carrying in materials with which to line it. When they

had finished laying I took their five eggs, at the same time throwing

down the oven, and waited to see what their next move would be. They

remained on the spot singing incessantly, and still manifesting anxiety

when approached. I observed them four days, and then was absent from

home as many more; on returning, I found that the Leñateros had once

more disappeared, and that the nest was now held by the Bay-wings. I

also noticed that they had opened an entrance very low down at the side

of the nest which they were using; no doubt they had killed and thrown

out the young Leñateros.

 

It was now early in November, the height of the breeding-season, and

numbers of Common Cow-birds constantly visited the nest; but I was

particularly interested in a pair of Screaming Cow-birds that had also

began to grow fond of it, and I resolved to watch them closely. As they

spent so much of their time near the nest, showing great solicitude

when I approached it, I strongly hoped to see them breed in it, if the

Bay-wings could only be got rid of. The Screaming Cow-birds would

not, or dared not, attack them; and, as I always think that the worst

possible use one can put a little bird to is to shoot it, I could not

help them by destroying the Bay-wings. I therefore resolved to take

their eggs, hoping that that would cause them to leave in disgust.

 

When I was satisfied from their movements that they had finished laying,

I got up to the nest, and was astonished to find _ten_ eggs instead of

five, as I had confidently expected; for, though the Common Cow-birds

had paid a great deal of attention to the nest, I knew the Bay-wings

would not allow _them_ to lay in it.

 

The ten eggs in the nest were all unmistakably Bay-wing's eggs; and

having observed before that several females do occasionally lay

together, I concluded that in this case two females had laid in the

nest, though I had only seen two birds--male and female. After taking

the ten eggs the Bay-wings still remained, and in a very short time they

appeared to be laying again. When I had reason to think that the full

complement was laid, I visited the nest and found five eggs in it; these

I also took, and concluded that the second female had probably gone

away, after having been deprived of her first clutch. During all

this time the Screaming Cow-birds remained in the neighbourhood and

occasionally visited the tree; but to my very great surprise the

Bay-wings still stubbornly remained, and by-and-by I found that they

were going to lay again--the fourth time! When I next visited the nest

there were two eggs in it; I left them and returned three days later,

expecting to find five eggs, but found seven! certainly more than one

female had laid in the nest on this occasion. After taking these last

seven eggs the Bay-wings left; and though the Screaming Cow-birds

continued to make occasional visits to the nest, to my great

disappointment they did not lay in it.

 

April 12.--To-day I have made a discovery, and am as pleased with it as

if I had found a new planet in the sky. The mystery of the Bay-wings'

nest twice found containing over the usual complement of eggs is cleared

up, and I have now suddenly become acquainted with the procreant

instinct of the Screaming Cow-bird. I look on this as a great piece of

good fortune; for I had thought that the season for making any such

discovery was already over, as we are so near to winter.

 

The Bay-wings are so social in their habits that they always appear

reluctant to break up their companies in the breeding-season; no sooner

is this over, and while the young birds are still fed by the parents,

all the families about a plantation unite into one flock. About a month

ago all the birds about my home had associated in this way together, and

went in a scattered flock, frequenting one favourite feeding-spot very

much, a meadow about fifteen minutes' walk from the house. The flock was

composed, I believe, of three families, sixteen or eighteen birds in

all: the young birds are indistinguishable from the adults; but I knew

that most of these birds were young hatched late in the season, from

their incessant strident hunger-notes. I first observed them about the

middle of March. A week ago, while riding past the meadow where they

were feeding, I noticed among them three individuals with purple spots

on their plumage. They were at a distance from me, and I naturally

concluded that they were young Common Cow-birds (_M. bonariensis_),

casually associating with the Bay-wings. I was surprised to see them,

for the young male _M. bonariensis_ always acquires the purple plumage

before March, so that these individuals were changing colour five weeks

after the usual time. To-day, while out with my gun, I came upon the

flock, and noticed four of the birds assuming the purple plumage, two

of them being almost entirely that colour; but I also noticed with

astonishment that they had bay- or chestnut-coloured wings, also that

those with least purple on them were marvellously like the Bay-wings in

the mouse-coloured plumage of the body and the dark tail. I had seen

these birds before the purple plumage was acquired, and there was then

not the slightest difference amongst them, the adults and their supposed

offspring being alike; now some of them appeared to be undergoing the

process of a transmutation into another species! I at once shot the four

spotted birds along with two genuine Bay-wings, and was delighted to

find that the first were young Screaming Cow-birds.

 

I must now believe that the extra eggs twice found in the nest of the

Bay-wings were those of the Screaming Cow-bird, that the latter species

lays chiefly in the nests of the former, that the eggs of the two

species are identical in form, size, and colour, each bird also laying

five, and that, stranger still, the similarity is as perfect in the

young birds as it is in the eggs.

 

April 15.--This morning I started in quest of the Bay-wings, and

observed one individual, that had somehow escaped detection the day

before, assuming the purple dress. This bird I shot; and after the flock

had resettled a short distance off, I crept close up to them, under the

shelter of a hedge, to observe them more narrowly. One of the adults was

closely attended by three young birds; and these all, while I watched

them, fluttered their wings and clamoured for food every time the old

bird stirred on its perch. The three young birds seemed precisely alike;

but presently I noticed that one of them had a few minute purple spots,

and on shooting this one I found it to be a young _M. rufoaxillaris_,

while the other two were true young Bay-wings.

 

The hunger-cry of the young _M. badius_ (Bay-wing) is quite different

from that of the young _M. bonariensis_: the cry of the latter is a

long, shrill, two-syllabled note, the last syllable being prolonged into

a continuous squeal when the foster-parent approaches with food; the cry

of the young _M. badius_ is short, reedy, tremulous, and uninflected.

The resemblance of the young _M. rufoaxillaris_ to its foster-brothers

in language and plumage is the more remarkable when we reflect that the

adult bird in its habits, gestures, guttural notes, also in its deep

purple plumage, comes much nearer to _M. bonariensis_ than to _M.

badius_. It seems impossible for mimicry to go further than this. A

slight difference in size is quite imperceptible when the birds are

flying about; while in language and plumage the keenest ornithologist

would not be able to detect a difference. But it may be questioned

whether this is really a case of an external resemblance of one species

to another acquired by natural selection for its better preservation.

Possibly the young _M. rufoaxillaris_, in the first stage of its

plumage, exhibits the ancestral type--that of the progenitor of both

species. If _M. badius_ belonged to some other group--_Sturnella_ or

_Pseudoleistes_, for instance--it would scarcely be possible to

doubt that the resemblance of the young _M. rufoaxillaris_ to its

foster-brothers resulted from mimicry; but as both species belong to

the limited, well-defined group _Molothrus_, the resemblance may be

ascribed to community of descent.

 

Formerly I believed that though _M. badius_ is constantly seen rearing

its own young, they also occasionally dropped their eggs in the nests

of other birds. I could not doubt that this was the case after having

witnessed a couple of their young following a Yellowbreast and being

fed by it. I must now alter my opinion, for what then appeared to be

proof positive is now no proof at all, for those two birds were probably

the young of _M. rufoaxillaris_. There are, however, good reasons for

believing that _M. rufoaxillaris_ is parasitical almost exclusively

on _M. badius_. I have spoken of the many varieties of eggs _M.

bonariensis_ lays. Those of _M. badius_ are a trifle less in size,

in form elliptical, densely and uniformly marked with small spots

and blotches of dark reddish colour, varying to dusky brown; the

ground-colour is white, but sometimes, though rarely, pale blue. It is

not possible to confound the eggs of the two species. Now, ever since

I saw, many years ago, the Yellowbreast feeding the supposed young

Bay-wings, I have looked out for the eggs of the latter in other

birds' nests. I have found hundreds of nests containing eggs of _M.

bonariensis_, but never one with an egg of _M. badius_, and, I may now

add, never one with an egg of _M. rufoaxillaris_. It is wonderful that

_M. rufoaxillaris_ should lay only in the nests of _M. badius_; but

the most mysterious thing is that _M. bonariensis_, indiscriminately

parasitical on a host of species, never, to my knowledge, drops an egg

in