196 WET FOREST COMMUNITIES 
Farther north the blackburnian warbler nests here. The tree stratum 
of primeval conditions usually included the pine marten (Martes 
americana Tur.). It livesin trees in dark coniferous forests. Merriam 
(142) says that it nests in a hollow tree or log, rarely on the ground. 
It preys upon partridges, rabbits, squirrels, chipmunks, mice, shrews, 
birds’ eggs, young birds, and frogs and toads. It disappears when 
civilized man settles the country. The marten’s close relative, the fisher 
(Martes pennanti Erx.), is said to be the wildest of all wild animals. It 
is somewhat similar (21, 22, 162) to the marten in habits. 
c) The pine-birch transition girdle (Station 54; Table XLVI).—This 
succeeds the tamaracks and contains a few old trees of this species. The 
pools are all dry in summer, though they may contain water in spring. 
The subterranean stratum has not been investigated. 
The ground stratum includes the frogs of the tamarack formation 
(Hyla pickeringii). Insects, spiders, centipedes, and snails, which belong 
chiefly to mesophytic forest, are more numerous than in the tamarack 
stage. Nesting of the ruffed grouse likewise indicates that the swamp 
stage is past. The field and shrub strata likewise include more of the 
mesophytic forest animals than the true tamarack stage. 
The tree stratum has not been studied. The trees are white pine, 
yellow birch, and an occasional maple. Felt (137) records no insect 
common to these two trees. There are several common to the white 
pine and tamarack (larch lappet, engraver beetle, etc.). Pines have 
many borers and few leaf-feeders. Each borer usually prefers a certain 
part, as the trunk, limbs, or growing shoots; some, as the white-pine 
weevil (Pissodes strobi Peck) (161), attack young pines. Felt records 
about 25 injurious insects common to birches and maples in general 
and one or two which occur only on yellow birch. The great crested 
flycatcher nests in holes in dead limbs; the wood pewee nests on 
horizontal limbs, and the red-eyed vireo builds a nest in trees from 
5 to 4o ft. from the ground. Dead birches form suitable nesting- 
places for woodpeckers. The Canada porcupine (142) which we have 
noted in the ground stratum is a good climber and feeds largely in 
the trees, which it often girdles. 
d) The geographic relations of the animals—Most of the non-aquatic 
animals of the swamps are commonly said to belong to species common 
farther north where conifers dominate. However, our lists and the 
unpublished work of Messrs. Wolcott and Gerhard do not bear out this 
conclusion. Some of the species of these swamps doubtless formerly 
occurred among the hemlocks of Southern Michigan. 
