The Sparrow Hawk: Open Ridges
Even at 6 o'clock this early August morning, the sun
is hot on Greenstone Ridge. Rising red above Lake Superior it sends its
rays unopposed against the open, rocky slopes, further drying the
grasses and slowing the activity of animals.
But though it is hot on the open ridge east of Mt.
Ojibway, there is some action. Perched in a hazelnut thicket, a song
sparrow sings. In another thicket, a red squirrel rustles, searching for
curve-beaked hazelnuts. Atop yet another, a Traill's flycatcher gives
its short little call, advertising its territory, though its young and
those of other flycatchers are on the wing and wandering. In the
Greenstone Trail between two thickets a snowshoe hare nips wild
strawberry leaves. Far down the slope, a red fox picks its way between the
shrubs, alert for hare, bird, or mouse; if unsuccessful, it will descend
into the forest for wild sarsaparilla berriesa never-failing
resource this time of year.
![](images/nh8bb.jpg)
(Photo by J. Wiessinger)
At the tip of a dark spruce tree, a young sparrow
hawk perches awkwardly, crying for food. But the hawk's parents are busy
hunting. The trim female sits on the limb of a dead aspen, studying the
ground. Her sharp eyes scan the rocks, grey-green with lichens and
crevice-lined with grass and bush honeysuckle. Out of the
grey-green-brown background she discerns an interesting shape. She
plummets to the rock and seizes a grasshopper in her talons, then
returns to her perch. Seeing all this, the young bird flutters to the
aspen, but approaching the limb too fast can't hold on and pitches
forward. It circles around, and on the second try manages to land. The
mother bird rewards it with a mangled grasshopper.
![](images/nh8bc.jpg)
Grasshoppers, along with mice, are favored prey of
the sparrow hawk. (Photo by Wm. Dunmire)
|
The male sparrow hawk cruises above the ridge toward
the fire tower, now flapping, now gliding, now hovering to inspect
something below. He sees many things, but not all are significant to
him. In a thicket of red maple, juneberry, and hazelnut a dark brown
shape resolves into a bull moose intent on getting a last few mouthfuls
before the heat drives him down into the forest. Across the trail, an
oval depression remains in the grass where the bull slept part of the
night. Farther along, the hawk sees two sharp-tailed grouse pecking at
flower buds, berries, and insects. The grouse, too, will soon seek
shade. Briefly, the sparrow hawk slows in his flight as he passes over a
family of flickers stabbing the ground for ants, a cedar waxwing
flycatching in the air, a robin caroling one last time this morning. But
these are all too big for the hawk. He speeds on, searching for a
sparrow, warbler, grasshopper, deer mouse, or red-bellied snake.
Then a dark shadow crosses the ground. The sparrow
hawk looks up, climbs, then dives on the much larger red-tailed hawk.
The redtail evades the rush and hastens on, eager to be free of its
small tormentor. The sparrow hawk pursues it as far as the fire tower,
then turns and glides back toward his family. The sun highlights the
reds and blues on his back and wings.
Far out and below the sun, white cottony fog creeps
across the surface of the lake. Soon it will envelop the island,
blotting out the ridges and valleys, the lakes, the forest. Today fog,
tomorrow wind, next week a storm will interrupt the heat that prevails
on the summer ridges.
This piece of Greenstone Ridge is one of the larger
open areas on Isle Royale. Similar openings occur frequently on other
parts of Greenstone Ridge and on Minong and Feldtmann Ridges, with small
patches scattered elsewhere. Generally, these nonforested strips are the
result of fire aided by erosion and drought. Ridgetops, being the
highest land on the island, frequently are hit by lightning, which
sometimes starts fires. After a fire, the denuded soil is easily eroded.
On any slope, erosion continually occurs on a small scale, but the
lower parts also continually receive soil from upslope. On a ridgetop,
of course, there is no higher source. Here, creation of new soil must
proceed faster than erosion in order to make any headway. Organic debris
is the principal building material of soil on ridges, but vegetation is
discouraged by the thinness of the soils and the dryness caused by steep
slopes, sun-heating, and wind. If plant succession does proceed toward
forest, fire promoted by the dryness may at any time set it back. Thus,
the ecologic dog has itself by the tail, and some stretches of ridgetop
may remain open for many years.
![](images/nh8bd.jpg)
(Photo by R. Janke)
The plantlife on open ridgetops is mainly that
characteristic of early stages of succession, as described in chapter
seven. Such places are usually a patchwork of bare rock, grassy areas
with small shrubs such as blueberry and bush honeysuckle, shrubby
thickets of hazelnut, juneberry, and sometimes young red and sugar
maples, and scattered trees representative of the surrounding
forest.
The animal life is also distinctive, and some species
are restricted to such open areas. The larger animals are those found
throughout the island. Moose most often visit the open ridges in early
spring, when some herbaceous plants are sprouting and two favored
shrubs, hazelnut and juneberry, are leafing. Hares enjoy the abundant
low growth throughout the year but particularly in the green seasons.
Wolves take advantage of the easy traveling on ridges, turning aside
when a moose is started. Red foxes hunt fruits as well as live prey. Red
squirrels sometimes visit the thickets, apparently for their seeds and
fruits.
On the other hand, many of the birds of open ridges
are pretty much restricted to this type of habitat. Sparrow hawks,
which rely heavily on large insects such as grasshoppers, are typical
inhabitants, often nesting in old flicker holes in dead white pines.
Chipping sparrows, bluebirds, starlings, robins, cedar waxwings, and
chestnut-sided, mourning, and Nashville warblers also favor this kind of
environment.
The sharp-tailed grouse, though uncommon, is perhaps
the most typical bird of this environment. These large, grey-brown birds
with short, pointed, white-fringed tails would disappear if forest
claimed the entire island. Though good habitat for them is available,
their presence on the island is still something of a mystery. The other
grouse of the mainlandruffed and spruce grousehave not been
able to colonize the island because they can't make flights of more than
a half-mile or so. How did the sharp-tailed grouse manage it? Possibly
it was introduced by islanders of the past who wanted a game bird to
hunt. More likely, the sharp-tail, a stronger flier than the other
grouse, came under its own power, alternately sailing and beating its
short, rounded wings.
Isle Royale's ridgetops thus offer the hiker the
opportunity to explore a distinctive environment in all stages of plant
succession from bare rock to mature forest. He will enjoy wild
strawberries in early summer and blueberries in late summer, as well as
incomparable views of the island, the big lake, and the mainland hills;
and he will experience the ever-changing weather that presides over
all.
|