24. Tur Witson BULLETIN, No. 74. 
groups of plant associations, they are quite likely to be and 
most birds pursue all their summer life activities within the 
same plant formation. 
In certain cases bird activity is one of the prime factors in 
causing plant succession which in turn is followed by a change 
in the character of the bird population. Such is obviously the 
case in the transition from the black oak to the mixt forest 
associations, in which the birds play the role of seed distrib- 
utors of the vines and shrubs which hav given rise to a most 
prominent characteristic of the mixt forest. 
Studies similar to this in restricted areas thruout the coun- 
try and in every season of the year are necessary in order to 
obtain a clearer insight into avian ecology. 
