145 
Wuy Do Our Brrps MIGRATE. 
D. W. DENNIS. 
It is insectivorous and “therefore” a migrant, is a common phrase in 
literature about migrants; it is the purpose of this brief paper to take 
the therefore out of of this sentence; to maintain that what a bird eats has 
bothing to do with the great bird movement from the south to the north 
in the spring and back again in the fall after breeding. 
The Pennsylvania reed bird, the bobolink, doubtless stops at the reed 
swamps in Pennsylvania for refreshments on its way south; the South 
Carolina rice bird, another name for the bobolink, takes toll of the rice 
swamps; but no one thinks that the reeds or the rice are the cause 
of the migrations. Surely if they had not wings, they could hardly fly 
from the equator to Manitoba, but this does not make their wings the 
‘cause of the journey; nor is their food the cause. 
It is stoutly maintained that climate is the cause. ‘This, like wings 
and food, renders the journey possible; but it cannot in all cases cause 
it, for many water birds, like the gannet and the petrel, go to their breed- 
ing grounds from colder to warmer water and many from warmer to 
colder. They go to inhospitable, inaccessible rocks that they may nest in 
a place of safety, as I believe. 
I was impressed at Wood’s Hole in the summer of 1901 to see tern 
flying by in great numbers every morning. Later I visited their breeding 
grounds at Penikese; they were flying by Wood’s Hole to get food for the 
day; they had not come to Penikese for food, for they came in such num- 
bers that they overtaxed the fishing grounds for more than twenty miles 
to the eastward. They had not come for climate, for they had come from 
all available areas, colder as well as warmer. VPerhaps it is admitted that 
they came to lay their eggs and rear their young safe from destructive 
mammals, including boys. 
10—4966 
