102 Bulletin Wisconsin Natural History Society. [Vol. 10, Nos. 1 & 2. 
It is a common habit among birds for the young to congre¬ 
gate in flocks after the breeding season, often some time before 
the migration flocks of older birds begin to gather, so that the 
mere gathering of birds may not furnish any proof on the migra¬ 
tion habit. Nevertheless, the requisite food supply becomes a 
greater problem with a concentration of young or old birds in 
large numbers and this must have considerable effect on the forag¬ 
ing instincts. The desire of birds to keep together forces them 
to seek the very best feeding grounds in order to provide sufficient 
food for the larger numbers. 
Until recent publications of the Biological Survey, the lack of 
definite data as to the exact species of insects and seeds which a 
larger number of our migrants devour, has made it impossible to 
specialize on the requirements of each species for each month in 
the year. Most birds have a quite different food supply during 
the flocking season than that during the nesting period, if one 
mean thereby the exact species of insects or plant seeds consumed. 
It must be evident to any one that there will be considerable varia¬ 
tion in the supply of any particular species, especially in insect 
life. Is it not possible that some birds may leave feeding grounds 
for the South, not because of the lack of all of their food supplies, 
but through the lack of those items which are most liked, especially 
if any of their scouts discover larger supplies to the southward? 
While wintering on the bluffs of the Arkansas River, East of 
Ponca City, Oklahoma in 1906-7, I was interested to note the local 
migrations of ducks up and down this river valley throughout 
that season. This region is, of course, in the latitude of the 
Northern boundary of our Northern ducks during their winter 
sojourn in the South. During two or three slight cold spells, ice 
formed on the river and on such occasions, flocks of ducks going 
Southward were noticeable. With every recurring warm spell 
and breakup of ice, flocks of ducks were seen going Northward. 
With the spring breakup of ice when large masses came down 
the stream, some even from Colorado, larger flocks of ducks were 
seen going Northward. After that time, no further flocks of 
ducks were noticed going Northward. The slight variation in 
temperature shows at once that the hardy ducks were not particu¬ 
larly influenced by cold as a factor, but a more probable reason 
would be the freezing over of the water so that they could not. 
