It’s only a few weeks until the end of summer, a terrible time to be a moose in the New Hampshire wild.

Tens of millions of winter ticks are preparing to hatch next month from eggs hidden in thick brush. They will wait there to hitch a ride on a moose and suck its blood until the end of May.

They can send a moose to its death, with up to 150,000 dining on every calf, cow and bull in certain parts of the Granite State, wildlife biologists estimate.

There was a time when eggs laid in this age-old cycle perished on winter snow. But that hasn’t happened lately in New Hampshire, where a warming trend has winters starting later and ending sooner.

A single female lays 3,000 eggs the size of salt crystals. With warmer weather, ticks don’t die, they multiply.

Winter ticks are one-host parasites that feed on a single animal through their lifetimes. As the number of ticks explodes, moose have disappeared by the thousands in areas where they were most abundant. Many of those still alive are eerily thin, with rib cages visible through ragged skin. They are mere shadows of themselves, zombies with antlers.

“It’s pretty depressing,” said Kristine Rines, a wildlife biologist and moose project leader for the state’s Fish and Game Department. “It’s a pretty tough way to go. There’s no question that climate plays a huge part in this. If we had winters that lasted as long as they used to, we might not be having this conversation.”

New Hampshire’s struggle with moose is part of a nationwide trend, according to the Wildlife Management Institute, a nonprofit group established by sportsmen and businessmen concerned about wild populations.

A rise in moose die-offs has been reported in Minnesota, Montana, Wyoming, other parts of the Rocky Mountains and a sliver of North Dakota. In Montana, Minnesota and North Dakota, it’s not clear that ticks are the entire problem, leaving scientists baffled over why so many moose have fallen.

Only Maine, where colder winters and snow still kill ticks, is showing a population increase, with more than 75,000 in the state’s range.

Moose are the largest of the deer species, with bulls that top 1,800 pounds and grow antlers 6 feet wide.

The impact of reduced moose populations reverberates through an ecosystem. Moose serve as walking lawn mowers, clearing brush and creating spaces for smaller species, such as rabbits and birds, to hide from predators. Moose also provide hearty meals for coyotes and bears; a single carcass can feed these animals for days.

But loaded with ticks, they scratch until their fur falls off. They develop anemia and starve, Rines said.

They eventually become so stressed from tens of thousands of tiny bites every minute and every day that they can’t eat even if food is handed to them. “They look terrible. Their body weights are down. They have secondary skin infections from multiple bites,” Rines said, and they lose so much fur that they freeze whenever the weather manages to turn cold.

“In the central and White Mountain portion of the state where winters are short, we’ve seen a steady decline over the past five to seven years,” Rines said. The state’s moose population is about 4,500, at least 3,000 fewer than five years ago.

New Hampshire Fish and Game’s Wildlife Journal magazine wrote about the moose die-off from tick infestation in 2011 under the headline “Ghost in the Woods.” Moose-watching tours generate $115 million yearly in New Hampshire, but operators say current tours last hours longer than in past years as they seek to spot a single moose.

Minnesota’s moose mortality rate is so high that the state canceled its annual hunt in February. The decision followed a 35 percent decline in Minnesota’s moose population in a part of the state where it was strong, from 4,200 animals to 2,700 in a one-year survey that started in 2012.

Wildlife officials in Minnesota kept coming across moose carcasses of all ages that haven’t been scavenged. Studies were inconclusive, but indicated that the problem was health-related.

The Minnesota Department of Natural Resources plunked down $1.2 million to study why the animals continue to die. Previous research showed Minnesota’s mortality rate was far higher than in other states. Over several years in the late 1990s and 2000, 8,000 moose disappeared in the state’s northeast and 4,000 vanished in the northwest.

“I don’t think [ticks] are driving our decline,” said Erika Butler, a wildlife veterinarian for DNR who’s leading the study. “Our animals are in extremely poor body condition … but reproduction is high,” indicating that animals are strong enough to mate and reproduce.

So what’s happening between that time and when they drop dead? “A lot of folks suggest to us the brain worm parasite,” Butler said. But it could also be mosquito-related viruses or a fungus.

This year, state wildlife officials caught 111 moose and fitted them with collars with gadgets that send text messages when moose keel over and die.

The device has an accelerometer that measures movement. Scientists also opened the mouths of the animals and dropped in a transmitter that goes directly to the stomach and measures body temperature and the heartbeat. As soon as the animal’s vital signs indicate it has died, a text message is sent.

Of the captured moose, 18 have died. Three deaths were caused by ticks, some moose were eaten by predators, and others are still being studied.

“We’re studying every piece of their body [with] field necropsies. Every organ you can name: eyeballs, brain, liver,” Butler said. A “moose fleet” — helicopters, snowmobiles, all-terrain vehicles — rush to fresh bodies “so we can get the carcasses out whole,” she said.

Minnesota’s winters are colder than New Hampshire’s, where the cause of moose mortalities is certain. In New Hampshire, Rines said, when short winters allowed the tick population to thrive, “we had years where almost none of the calves survived and only 25 percent of adults.”

New Hampshire recently launched a $695,000 study of its moose population. In 2001, the state first saw problems that led to the first remarkable die-off. “Since then, it’s been an uphill battle against them,” Rines said of the ticks. “Our winters have gotten unfortunately more reliably short.”

At 400 pounds, moose calves aren’t lightweights. But “those animals would have to replace their blood volume” while hosting 100,000 ticks in winter when food is scarce, Rines said.