Blood-engorged, female tick after it has fallen from a moose (above). With a blood meal, it will now lay eggs in the soil - eggs that will hatch next fall. The green are balsam fir needles.
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 horrific 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.
Ticks cause moose to lose their hair throughout the winter (above).
These members of the deer family are also minimally impacted by winter tick. By contrast, moose are new comers 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 tick.
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 can cause a heavily-infested moose to die (above).
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 observe hair-loss patterns on as many different moose as possible. Through binoculars, we carefully observe moose. With cameras, we photograph them.
From these observations and photos, we draw patterns of hair loss onto data sheets. We digitize these data sheets to estimate the proportion of hair lost on each moose. Each spring we document hair loss patterns on 60 to 90 moose, which represents about one out of every ten moose alive on the island.
It is 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.
The first decade of monitoring (see graph at bottom left) suggests that high and increasing levels of tick abundance may indeed play a role in cause moose abundance to decline.
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. Five of the past six summers (2001-2006) have been the hottest summers in the history of the project (1958-2006).
What causes the climate to warm? An enormous amount of scientific evidence indicates that our use of petroleum causes climate warming.
The first decade of monitoring (see graph above) suggests that high and increasing levels of tick abundance may indeed play a role in cause moose abundance to decline.
It is reasonable to believe that humans, through our excessive use of automobiles and other fossil-fuel burning activities, are having a profound impact on the balance of wolves and moose on Isle Royale - an impact mediated by an invertebrate the size of your fingernail.
The sad part of this story... This example of climate change impact is in many respects minor compared to other problems the climate change are likely to cause - rising sea level, more severe hurricanes, disrupted systems of food production for humans, and the spread of diseases that depend on warmer weather.