80 Migratory Instinct. [ ZOE 
destroyer collecting around the swarm, represented by beast and 
bird; second, the gregarious destroyer multiplying in the midst of 
an ample supply of food, represented by the carnivorous insect; 
third, animal and vegetable parasites developed inside the grasshop- 
per, and acting in the shape of an epidemic, or, better, epizootic; 
fourth, the migratory instinct leading the destroyer to his own per- 
dition. 
MIGRATORY INSTINCT IN CAGED WILD BIRDS. 
BY W. OTTO EMERSON. 
I have raised from the nest several pairs of black-headed gros- 
beaks ( Habia melanocephaila) during the past three years, that have 
shown me how true remains the migratory instinct in birds even 
when kept in confinement. 
I will attempt to give such notes as I have observed regarding 
these birds and their evident desire to migrate twice each year. 
Of three fledglings taken in June, 1885, two males grew to be 
strong, handsome singing birds. By fall these grosbeaks began to 
show a desire to fly, but at night only, between the hours of eight 
and nine, sometimes as late as ten o'clock. It was not possible to 
quiet them by any means, and for long afterwards it did not occur 
to me that this was the premonition of migration showing in these 
young birds. 
The uneasy flight of these grosbeaks was not caused by the pres- 
ence of strange cats, dogs or other animals liable to provoke such 
a commotion among them after dark. Again it was not caused by 
the troublesome bird-lice which sometimes makes canaries so un- 
easy after dark. No amount of cover over their cage or the plac- 
ing of it in the darkest part of the house had any effect towards 
quieting them. 
By the following March, 1886, I had about forgotten this uneasy 
disposition of the grosbeaks, when one warm, spring-like evening, 
as the cage hung at the east porch, they all at once commenced an 
uneasy fluttering of their wings as though suddenly waking up to 
the instinct of migration, if I may so express it. They kept moving 
_ back and forth in the cage, calling to one another in lonesome notes 
such as I have often noted in the migrating wild birds when passing 
overhead during the early evenings at my home in Haywards, Cal. 
They would continue this restless moving for some time, then 
