Warm winters like the one that just passed are likely to become more frequent as the planet heats up, scientists predict, and many of the consequences could be dire, from rising sea levels to droughts to the spread of pests and diseases. But in the lesser-noted ledger of global warming, there are also potential benefits for wildlife.
Among the potential beneficiaries is the New England cottontail, an endangered brown rabbit that, in a typical winter, stands out against the snow, making it an easy target for predators. Not so this nearly snowless year.
Warm winters can mean more vegetation, which in turn can provide a greater food supply for a range of herbivores in New England. That could benefit white-tailed deer, fishers, opossums, and bobcats, scientists say.
“Severe winters tend to limit many species of wildlife, because they suffer increased mortality due to cold temperatures and reduced availability of prey,’’ said John Organ, chief of the division of the wildlife and sport fish restoration for the US Fish and Wildlife Service in Hadley. “Increased warming trends, resulting in reduced snow, are likely to allow more species to have a higher survival rate. All things being equal, that might mean increased populations, unless compensated by an increase in mortality factors such as disease.’’
Scientists say some species of butterflies may benefit from warmer winters, allowing them to spawn successive generations in a life cycle, rather than just one.
Reduced snowfall may mean deer no longer congregate in small areas and therefore will not be such easy prey. Young bobcats and fishers may be less susceptible to starvation because of the difficulty of navigating through deep snow.
Also likely to thrive as the season grows less harsh are red-bellied woodpeckers, geese, and turkeys, which are pushing farther north than ever before. Migratory birds such as red knots are already benefiting from the earlier spawning of horseshoe crabs, whose eggs they eat.
And there is already evidence of the Virginia opossum moving farther north in New England and Canada, even though they are occasionally found dead from frostbite because they are not accustomed to the deep cold.
Of course, climate change will present a trial for a number of species. Snowshoe hares, unlike the New England cottontail, are more vulnerable without snow, as their fur turns white in winter, rendering them more visible to predators.
Moose are more likely to suffer from ticks, which survive in far greater numbers when the weather remains mild. Black bears are less likely to hibernate, which affects their metabolism, potentially hampering their ability to reproduce.
This winter’s lack of snow - just 9.3 inches fell in Boston, nearly 80 percent below normal and the second lowest on record - has left many of the state’s rivers and streams at record low levels for the time of year.
It is also making it harder for freshwater fish such as shad, herring, smelt, and salmon to spawn and easier for algae to bloom, which depletes oxygen and makes it harder for river life to thrive.
For the New England cottontail, a bark-colored rabbit with perky ears and tails like puffs of cotton, it may be years before scientists see the benefits of warmer winters.
Although they say there are signs of increasing numbers on Cape Cod, they believe there are fewer than 500 left in New England. The rabbit - the only cottontail native to the area - has already vanished from Vermont and nearly all of its New Hampshire habitats. Its historic range, from Maine to New York, has shrunk by more than 85 percent and it may be eligible in two years to be added to the nation’s list of endangered species, the only candidate for such federal protection in New England.
“When we lose a species like the New England cottontail, we lose a piece of our heritage,’’ said David Scarpitti, a wildlife biologist with the Massachusetts Division of Fisheries and Wildlife, who is part of a regional group trying to save the rabbit from extinction. “We don’t know what the consequences would be if we lose all of them. There’s a delicate balance of nature.’’
In recent years, as the rising amount of development has reduced the rabbit’s habitats throughout the region, state and federal officials have sought ways to protect the New England cottontail, which is not to be confused with the similar-looking, nonnative, and far more abundant Eastern cottontail. The Eastern cottontail, which was brought to New England by trappers in the 19th century, has apparently flourished because it has better peripheral vision than the native bunny, allowing it to hop to safety more quickly.
Last month, the US Departments of Agriculture and the Interior announced they would spend $33 million to restore and protect the habitats of seven at-risk species around the country, including the New England cottontail. Some of the money will be spent over the next five years to remove invasive plants and improve about 2,500 acres of land throughout the region to provide a more natural habitat for the rabbit, which thrives on munching twigs in shrub lands and regenerating forests.
But it will be a challenge to save a species that is elusive, has already fallen to such low numbers, and faces many predators, including raptors, owls, bobcats, and foxes.
Scientists are hoping rising temperatures and more low-snow winters will allow the rabbits to blend in better and be less visible to their prey.
“If there are fewer days in the year with snow, we would expect the survival rate to increase, and we’re hopeful that this winter provided some help,’’ said Anthony Tur, an endangered species specialist at the US Fish and Wildlife Service in Concord, N.H.
He added: “It can use all the help it can get.’’