Moose Threatened by Blossoming Tick Populations
March 25, 2013 -
Region— As long, cold winters become less certain, elevated numbers of winter ticks may be straining the population of New England's largest and most iconic land mammal: the moose.
Tick infestation isn't uncommon for moose, but as larger numbers of the arachnids survive the colder months, some moose populations in southern areas of Maine and New Hampshire could be impacted.
Moose, covered with tens of thousands of ticks become anemic from blood loss, exhausted and stressed from the discomfort, leaving themselves open to infection, hunger and exposure.
Although wildlife biologists can't say for certain to what extent ticks are affecting the moose population, it is clear that a combination of high moose densities and mild winters are giving winter ticks a leg up.
Unlike "dog" and "deer" ticks, winter ticks are a single-host species, that rely on one animal throughout their entire life cycle.
In early autumn, groups of thousands of larvae, no larger than a grain of sand, "quest" for a host, climbing bushes and small trees in the undergrowth and waiting to attach to large mammals.
After finding a host, the tick larvae take their first blood-meal, morphing into nymphs and then adult ticks through the winter months.
By early spring, engorged females drop from their hosts and lay eggs, which hatch in June.
Moose infested with ticks isn't uncommon, says Lee Kantar, Maine state moose biologist. What's changed is the number of ticks that survive winter.
A typical cold, wet Maine autumn kills off questing larvae, but a milder autumn gives them a chance for survival, Kantar says.
Similarly, the arrival of an early spring with little snow on the ground means more female ticks will survive to lay eggs.
"You have this scenario where if you have a mild fall and an early spring with little snow, the next fall will be a year of plenty for winter ticks," Kantar says.
The concern is that short winters are becoming more common, leaving moose, the most attractive tick host, at risk.
Quirks of evolution and behavior make moose particularly susceptible to tick infestation, says Kristine Rines, the head of New Hampshire Fish and Game's moose program.
Moose breeding season is in October, so the animals are most active at precisely the same time clusters of tick larvae are waiting for a host in the underbrush.
Moose also have woefully inadequate grooming skills compared to other tick-prone mammals like deer, Rines explains. Research suggests the poor grooming may be a result of a shorter evolutionary relationship between moose and winter ticks.
Another factor driving winter tick infestation is the density of moose in a given area – more moose mean more opportunities for ticks to latch on and survive, leading to larger tick numbers.
"As moose densities have grown so have tick densities," says Rines. "We've got this perfect storm where all of a sudden we don't have winter like we need ... it's just given ticks this perfect edge."
When tick populations explode, so do the numbers infesting moose – in a "bad winter" a single moose can have between 120,000 and 160,000 parasites, Rines says.
Moose health is compromised partially by the sheer discomfort of so many parasites. Heavily-infested moose rest and eat less, and spend more of their time trying to get rid of the ticks.
In another cruel twist of fate, adult ticks are feeding during the winter months, when moose can least afford to be wasting energy trying to remove them, Rines says.
Those effects are compounded by the blood loss from the ticks, leaving weakened moose susceptible to other parasites, disease, or exposure.
Even trying to remove the hangers-on damages moose health – the animals will rub so ferociously that their thermal coats are destroyed, further endangering their health.
Tick-ravaged moose have been given the moniker "ghost moose" to describe the sight of emaciated beasts in the spring, covered in broken, white hair.
Big tick numbers can be much more deadly for smaller, slighter calves, and a bad tick winter can ravage a population of young moose.
"Calves may have to replace their blood volume once and possibly twice," says Rines. "That takes a lot of energy that they simply don't have."
Moose at risk?
It's hard to quantify the impact recent mild winters have had on Maine's moose population, Kantar says. In fact, it's pretty hard to know how many moose even live in the state.
As an example, Kantar says, Maine Department of Inland Fisheries and Wildlife estimated for two decades there were 29,000 moose statewide.
By applying new survey techniques, the estimated number of moose has more than doubled – Kantar says MDIFW approximated 76,000 moose this autumn. The population increase may be the result of a growth of ideal moose habitat, Kantar says.
If it's that difficult to predict the moose population, it is even harder to pinpoint moose die-offs from winter ticks.
The impact also varies between winters, Kantar says – some are going to be harder on moose than others – it's hard to tell what will happen if mild winters become the norm.
There is evidence, however, that a bad tick winter can have a devastating effect on moose populations.
According to Rines, during one particularly good tick year during a 2002-2006 study in New Hampshire, nearly all of the collared calves and 20 percent of the adults died.
Her biggest concern is that New Hampshire now has a high tick "background level" which makes the "eruptive" tick years even harder on adult females, who are either not becoming pregnant or are having fewer offspring.
"They are at high enough background levels that the increased mortality and reduced reproductive output they're causing is really impacting the population," Rines says.
There might not be a great solution to ballooning winter tick populations – once established a big tick population is hard to address, even with pesticides.
Dealing with the tick population relies on reliably cold winters and low moose population density – only time – and the weather – will tell what happens to New England's most famous forest denizen.
Peter L. McGuire, Advertiser Democrat, March 2013
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