Small Creatures, Big Influence
Small Creatures, Big Influence
On Isle Royale, this creature survives by the blood of moose and no other animal. Its existence depends entirely on moose. It weighs only one millionth the weight of a moose, and consumes just a fraction of an ounce of blood during its lifetime. This is Dermacentor albipictus, the moose tick.
D. albipictus may cause as much, if not more, suffering for moose than wolves or starvation. Each winter, 80,000 ticks, or more, may live on the skin of a single moose. Moose sacrifice gallons of blood and much of their thick insulating fur to give life to these little creatures.
Winter ticks typically live only on members of the deer family and are found only in North America. This tick species evolved with members of the deer family, like white-tailed deer and elk. These members of the deer family have inhabited North America for millions of years.
White-tailed deer and elk are also minimally impacted by winter tick. By contrast, moose are newcomers to North America. They first came to North America about 10,000 years ago. Because they are newcomers, they are not well adapted to deal with winter ticks.
The life cycle of winter ticks is also distinctive. During the summer winter ticks exist only as unhatched eggs in the soil. In autumn, the ticks hatch, crawl to the tops of grasses and wait to latch onto any unsuspecting moose that walks by. These young ticks feed and grow on the moose during the winter. In early spring, the ticks mate, the males die, and the females drop from the moose to the soil where they lay their eggs.
Ticks weaken moose and make them vulnerable to starvation and wolf predation. At the turn of the century, we began to wonder, could D. albipictus be a powerful influence on the population dynamics of moose and consequently wolves and the forest. To find out we had to develop a way to quantify the level of tick infestations each year. Here’s the method we developed:
During the first five weeks of each summer field season, until mid-June, moose still have their winter coats which are damaged from ticks. During this time, we observed hair-loss patterns on as many different moose as possible. Through binoculars, we carefully observed moose. With cameras, we photographed them.
From these observations and photos, we drew patterns of hair loss onto data sheets. We digitized these data sheets to estimate the proportion of hair lost on each moose. Each spring we documented hair loss patterns on 60 to 90 moose, which represented about one out of every ten moose alive on the island.
It was a race against time, to see so many moose. Every year, within a few days of June 18th, moose coats transform from sad-looking and tick-damaged to beautiful, thick, and shiny, with no trace that they have ever been affected at all by ticks.
In this way, ticks seem to have an important influence on moose, and consequently, wolves. The impacts don’t stop here. Ticks also affect much of Isle Royale’s vegetation: The vegetation that moose prefer, various shrubs species and balsam fir, have been exhibiting increased growth now that moose abundance is low. Ticks appear to have a tremendous influence on much of Isle Royale’s community through their impact on moose.
So, what factors determine tick abundance? Warm springs, warm summers, and warm falls are likely to favor ticks, and temperatures on Isle Royale are rising.
