balsam fir, highbush cranberry, moun¬ 
tain ash, and other species grow lux¬ 
uriantly (figs. 6 and 7). 
An extensive and widely distrib¬ 
uted habitat is furnished by the ir¬ 
regular shoreline of Isle Royale, the 
inland bodies of water, and streams 
and beaver ponds. The shoreline of 
Xale Royale is mostly rocky, and ex¬ 
cept in protected bays and coves the 
water may be quite turbulent. Beaches 
are scarce and while there are some 
sand beaches (fig. 8) most of them 
are coarse gravel (fig. 9). Inland 
lakes provide shoreline habitat sim¬ 
ilar to the island's shoreline (fig. 
2), but generally less subject to 
wave-washing and pounding. Inland 
streams and beaver ponds provide 
aquatic habitat (fig. 10). The 
shoreline association is quite vari¬ 
able owing to the variety of plant 
and forest types found at the water's 
edge. Marshes are scarce on the 
island, and only a few water areas 
have characteristic marsh plants 
such as cattail or water lily 
(fig. 11). 
BIRD DISTRIBUTION AND HABITATS 
Isle Royale presents many inter¬ 
esting opportunities for the study 
of bird ecology because of its insu¬ 
lar position. Adams based his pio¬ 
neering treatise concerning the 
ecological succession of birds on 
the findings of the Biological Sur¬ 
vey of Michigan at Isle Royale (1^ 
and 2). 
The available habitats and 
niches on the island result from 
the major vegetative types as de¬ 
scribed above, and from a number of 
special situations determined by 
topography, physiography, or the 
actions of animals. 
The following is a brief de¬ 
scription of each of the major hab¬ 
itat types on the island, including 
mention of the most obvious birds 
associated with each habitat. Fol¬ 
lowing this is a reference chart on 
which all the birds are listed with 
their status, abundance, and habi¬ 
tat type. 
1. The sugar maple-yellow birch 
climax forest type, the most homo¬ 
geneous habitat on the island, pre¬ 
sents a fairly continuous canopy, 
both horizontally and vertically (cf. 
aspen-birch-conifer). An understory, 
mostly of sugar maple reproduction, 
fills in below the tree canopy so 
that there is little open space in 
the forest. Breeding species closely 
associated with this type are the 
red-eyed vireo, ovenbird, black- 
throated blue warbler, and the wood 
peewee. The ovenbird and red-eyed 
vireo are also abundant in other 
types, especially the spruce-fir- 
birch climax. 
2. The spruce-fir-birch climax 
forest type is variable. Some areas 
have closed canopies through which 
little light penetrates, resulting 
in a paucity of ground vegetation, 
and self-pruning of the trees. Gray 
and blue jays, Swainson's thrushes, 
and chickadees use the dead branches 
resulting from limited light, as 
perches« 
The more open stands permit 
development of an understory, which 
is favorable for other species, 
chipping sparrows for example. 
Kinglets, red-breasted nut¬ 
hatches, and several species of war¬ 
blers make use of the upper layer of 
the coniferous forest and are pre¬ 
sumably little affected by the pres¬ 
ence or absence of ground vegetation. 
3. The aspen-birch-conifer 
type presents a much more open canopy 
than the sugar maple-yellow birch 
climax, and has a more definite strat¬ 
ification of elements. The canopy is 
7 
