100 BIRDS OF LA PLATA 
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 them- 
selves, 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 Firewood-Gatherer’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 Lefatero, 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 their victims left 
it for some days. Six days after I had picked up the 
ill-treated female, the builders of the nest came back 
