Moose numbers in decline due to overhunting, by ticks

A moose in the Vermont woods. Vermont Department of Fish and Wildlife photo
The encounter with the moose cow and calf, appearing out of nowhere, on a back road, late on a winter’s night, could have ended badly. But the consequences were minor — a skid, resulting from the over-application of brakes on a snowy road, followed by a brief standoff.
The staring contest, moose versus headlights, concluded. The moose, victorious, continued across the road. High-stepping in the deep snow with their long legs and odd, gangling grace, they disappeared into the forest.
Variations on this recent moose encounter play out across the state each year, and not always with such peaceful results. Fatal moose-motor vehicle collisions have served as a rough and counterintuitive guide to the health of Vermont’s moose population. The more collisions, the more moose — therefore, the healthier the population.
In the early 1980s, for example, when the state’s moose numbers were at a low, with fewer than 100 moose, there were two fatalities involving cars. In 2004, when the population had peaked at nearly 5,000, there were 182 (over the years, 19 humans have been killed in collisions with moose).
So the news that the numbers are down — last year there were only 30 fatal collisions — while good for those directly involved, has been a source not of relief but of concern.
Freefalling moose numbers is why the state’s fish and wildlife agency has called for cutting, to 14, the number of permits that will be given to moose hunters this fall. Last year, 40 permits were issued.
At a series of meetings conducted by the Department of Fish and Wildlife following the release of the numbers for the autumn hunt, it was clear that while deer have issues, too, their numbers and health are relatively stable. It is the state’s largest mammal — its icon of the northern forests — that continues to be of greatest concern.
After being hunted into near-extinction in the 19th and early 20th centuries, Vermont’s moose made a comeback only to be struggling again — their numbers more than halved from the high 15 years ago.
The initial reduction in the state’s moose population was deliberate. In the early 2000s, it was clear that moose were becoming victims of their own success. There were simply too many moose — 3,000 in the wildlife management areas in Essex County alone. They were making fast work of their own forest habitat by over-browsing, damaging the vast tracts of commercial forestland in northern Vermont, and they were becoming a nuisance to sugaring and farming operations, walking through fences, trailing strands of sap-tubing.
To reduce the population to a more sustainable level, the state’s biologists called for a substantial increase in the number of hunting permits issued annually. By 2011, they felt the population was where it needed to be, just below the ecological carrying capacity of the state’s wildlife management areas of 1.75 moose per square mile.
But then the numbers kept falling. The blame in northern Vermont has fallen on a new kind of colonizer, this one six-legged. The winter tick, Dermacentor albipictus, has been the beneficiary both of increased moose population densities and shorter, milder northern winters resulting from climate change.
In southern Vermont the culprit is another parasite — brainworm, a parasite carried by deer. Deer have evolved to live with brainworm, and the parasite’s host suffer no ill effects. For moose, brainworm is fatal. As deer numbers have grown, and deer have moved into habitat once solely occupied by moose — and as summers have become hotter and rainier, causing a rise in the population of the secondary brainworm host, a snail — brainworm has become more of a problem.
In northern Vermont, where deer densities are low, and moose densities are high, it is the winter tick — not to be confused with the deer tick, or the dog tick, which are problematic in their own way — that is taking over.
“It’s not uncommon, when you have higher moose densities, for the ticks to increase dramatically in number, for the simple reason there are more moose to feed on,” said Cedric Alexander, a wildlife biologist with the Vermont Department of Fish and Wildlife, and head of the state’s moose project.
Wildlife biologist Cedric Alexander displays a moose jawbone. Photo by Andrew Nemethy
From late autumn through spring, the moose is the winter ticks’ involuntary, and unhappy, host. As many as 50,000 or more ticks will overwinter on a single moose.
The cycle — for the moose — starts with the ticks in larval form. The larvae collect in clusters of hundreds, clinging to one another and to a branch or a bit of underbrush, and wait — a tactic known as “questing.” When a moose passes by, the larvae clamber on, and then latch on. They feed, molt into nymphs, feed again, and then, as fully grown adult ticks, they feed once more before dropping off in April.
These days no moose emerges unscathed from the onslaught of tens of thousands of the “blood sucking parasites” but while bulls may look terrible — mostly from attempting to scratch the ticks off — they are likely to survive, Alexander said.
Cows have a harder time. They are not only 20 percent smaller than bulls, but they also are carrying offspring, in the spring cows are in their third trimester — ticks have been blamed for an increase in aborted and still-born moose.
“But it’s the calves that are the ones really at risk,” Alexander said. Ticks are equal opportunity parasites; they cluster in equal numbers whether it is on a bull, a cow, or a calf. And because the calves are so much smaller, they lose proportionally more blood.
Recent autopsies on calves that have died for one reason or another, have found anemia, from loss of blood, to be a constant, underlying factor.
Moose are in poor condition in the spring, anyway; they’ve relied on their fat reserves to get through the winter, and by the time spring comes, they’re in a state of near malnutrition. “All moose, and deer for that matter, come April, they’re in a negative energy balance,” Alexander said. “The winter browse only helps slow the rate of fat depletion. The energy and protein in the winter browse is very poor.”
Among the most frequently asked questions at the meetings is can’t something be done? Is there nothing to stop the ticks? The answer, so far, is not much.
One factor that cannot be changed, biologists say, is the changing climate. The early autumn cold snaps, which once killed off larvae before they could attach to their hosts, happen less and less. As for the adult ticks dropping off in the spring — they’d die if they happened to drop into snow, but that also happens less and less.
There is a naturally occurring soil fungus known to be fatal to ticks, and research is underway to see whether there is a way to exploit it — but it’s a long way from practical application. “It would be a tremendous effort and a huge expense,” Alexander said, and even then it would hardly be a sure bet.
What biologists do know is that one way of controlling tick numbers is to control the density of the hosts — the moose. So it is ironic that the key to the herd’s survival may be the decline in moose numbers that is happening now. Just as a tick population explosion followed the increase in the numbers of their moose hosts, biologists are hoping that decreasing the population will hit a similar threshold, only in a downward trend.
The department’s proposed new target population density is 1 moose per square mile, instead of the previous target of 1.75 moose per square mile.
It is the reason the state is issuing permits for a limited moose hunt in the fall only in Essex County, where moose densities remain higher than the one moose per square mile target. It’s also the answer to the other frequently asked question, if moose numbers are falling, why hunt at all?
Fewer ticks will mean fewer health risks to moose. Given space, and time, the hope is, the moose will come back.
Read the story on VTDigger here: Moose numbers in decline due to overhunting, by ticks.