146 Bulletin Wisconsin Natural History Society [Vol. 13, No. 3 
The abundance of avian life in any habitat varies with the 
season of the year; so also does the relative abundance. From 
September until late November, which is the season of the 
fall migration, the swamp is the home of the largest number of 
species, with the woods second, and the open fields a fairly close 
third. During December, January, and February the birds 
found are: (1) permanent residents, or (2) winter visitors. 
Birds of the latter group are few in number, and the snow hunt- 
ing is an example. The former, such as the barred owl, great 
horned owl, chickadee, woodpeckers, nuthatches, are the wood- 
inhabiting species, and comprise by far the largest part of the 
winter forms. As a result of this, during the colder months 
the number of species found in the woods exceed the total 
number found in the open regions — the swamp and the open 
fields. With the spring migration, however, (at least with 
the beginning of the spring thaw which immediately precedes 
the migration) the swamp rapidly takes the lead in the number 
of species, and maintains it until the following late November. 
The comparative abundance of species in these three associations 
is shown in figure (7). 
VII. AVIAN MIGRATION 
Although it is not the purpose of this section to list the mi- 
grant species, or to give the dates of arrival of the different 
species of birds, a few remarks on the spring migration in this 
region may not be out of place. It is is an established fact that 
bird migration occurs in “waves;” that several or many species 
arrive together, usually over night. While the number of these 
waves may vary, it has been the writer’s experience that there 
are perhaps more often three big migration waves than other- 
wise, and that the interval between the first and second is greater 
than between the second and third. 
As an illustration of this the following data are given from the 
writer’s notes on the spring migration at Wooded Island, Jack- 
son Park, Chicago, for 1913: The first big wave occurred on 
the night of April 22, and the following morning fifteen species 
were recorded not seen previously that year. The second 
large migration occurred on the night of May 2, for the next 
day twenty-four new arrivals were listed. The third wave 
