The Birds’ Calendar | 
nous, which shall we consider the cause, and 
which the effect? The credit of the species 
seriously depends upon the answer. The fact 
that they show great courage and fidelity in the 
defence of their offspring when danger threatens, 
makes it a reasonable inference that they can 
only be charged with being practical rather 
than sentimental. 
The latest lingering migrant among the 
thrushes was the ‘‘ olive-backed,’’ the least at- 
tractive of all the thrushes in appearance, being 
of a uniform and dull olive color on the back. 
It did not finally disappear till the second 
week in June, and during the last week in May 
it was the commonest bird in the Park, not 
even excepting the robin. In the Ramble I 
could hardly go ten feet without stirring up at 
least one or two. Until just previous to their 
departure they uttered only an occasional harsh 
call-note, in striking contrast to that of the 
wood thrush, which is so delicious; but three 
or four days before they left I heard the first ef- 
fort of song, not full-voiced, but soft and veiled, 
as is often the case when a species begins to sing 
in spring. 
The appearance of a bird is positive—you can 
tell the day and hour ; its disappearance is neg- 
188 
