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Climate change-triggered ticks causing rise in ‘ghost moose’

Climate change-triggered ticks causing rise in ‘ghost moose’ (Image: Native Range, Inc.)
27 Nov
The unprecedented frequency of winter tick epidemics have resulted in a 70 per cent death rate for New Hampshire’s moose calves

In the late 1970s, the forests of northern New England, which span the US states of Maine, Vermont and New Hampshire, were devastated by an outbreak of spruce budworm, a species of moth that in total defoliated around 55 million hectares of forest, more than double the area of the UK. In response to the outbreak, landowners were forced to clear cut extensive areas of the forest, a move that proved controversial. Yet one animal, now beloved by New Englanders, was set to benefit. The new habitat created by the widespread tree-felling was perfect for moose which moved in to the area in abundance. Numbers of moose peaked in the mid-2000s, making the animal emblematic of the region.

There are still plenty of moose in New England – more than 60,000 – but over the last 15 years scientists and locals have noticed changes in the population. Daily reports of skinny, weakened calves as well as dead animals started to pour in, often from locals travelling on common snowmobile trails. As concern about the moose grew, one symptom in particular hinted as to the cause of the problem. Many of the moose were suffering from extreme hair loss, a condition known as ‘ghost moose’ due to their visible white skin. It was something residents had seen before and indicated that while the moose may have benefitted from one parasite with a hunger for trees, another insect was now busy killing them.

Moose1An adult cow moose photographed in early May in New Hampshire displays the typical hair loss associated with a high winter tick load. Their appearance is often referred to as a ‘ghost moose’ (Image: Dan Bergeron/NH Fish and Game Department)

The winter tick has been present in New England and implicated in moose declines for at least the last century. Rising concern resulted in a new survey of moose and ticks, carried out between 2014 and 2017 in the forests of New Hampshire, the results of which have recently been published. The researchers found that epidemics of ticks, known as epizootics, occurred in each of the three years surveyed. They also uncovered a mortality rate of 70 per cent for moose calves – two phenomenon that were undoubtedly linked. Taking into account the period before the study, epizootics have occurred five times in nine years in northern New Hampshire and central Maine. The relatively small population of moose in New Hampshire is estimated to have fallen from approximately 7,500 to 4,000 animals.

According to Peter Pekins, a professor at the University of New Hampshire and one of the researchers involved in the survey, these findings reveal an unprecedented number of tick flare-ups. ‘The shocking thing in the study is the frequency of what we term epizootics,’ he says. ‘They should be very abrupt periodic events. The frequency we noted has never been reported before, never anything like that.’ Pekins and the other researchers found that dead calves were usually emaciated and often harboured horrifyingly high tick loads – up to 90,000 ticks per calf. Each insect can remove 2-3mm of blood from an animal and so calves with infestations suffer from chronic blood loss and acute anaemia.

ticksA patch of hide shows a cluster of engorged adult female ticks (Image: Henry Jones/University of New Hampshire)

Pekins and his team have a theory as to why this increased frequency is happening and it all relates to climate change. Ironically, the winter tick actually thrives in warmer conditions. The ticks attach to moose as larvae during the autumn, when they crawl up plant stems and await a host. The larvae develop into nymphs and then adults and drop to the ground in April, having fattened up on the host’s blood. If cold weather kicks in later than usual it provides the larvae with a longer time period to attach to the moose and this is exactly what happened in the epizootic years. ‘We know that winter is starting later and later so what that effectively does is provide more and more time for these larval ticks to find a host. The loads on moose just get higher,’ says Pekins. He is very clear that despite these losses, moose are not an endangered species. As he points out, it’s not in the interest of the parasite to completely wipe out the host. But he does expect numbers of moose to drop, both as a direct result of calf deaths and because badly affected females suffer from delayed sexual maturation.

GhostmooseAs each tick can remove 2-3mm of blood, calves with infestations suffer from chronic blood loss and anaemia (Image: Peter Pekins)

Pekins’s goal is now to understand more about tick epidemics, with the ultimate aim of being to predict them and to assist forest managers. He also wants to use the moose as a powerful symbol. ‘There’s no survivor out there that looks great,’ says Pekins. ‘If you saw the “winning” animals in May, it’s like looking at the TV show The Walking Dead, they’re really moribund. To me the value of this story is to take this iconic animal and make it the poster-child of climate change in this region. That’s probably the biggest value we can get out of this because it is an icon. Everybody’s in love with moose.’

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