With summer now in full swing, you may occasionally encounter snakes during outdoor activities. Most people are familiar with the common species, like garter snakes and water snakes, but within view of the Boston skyline, surrounded by highways, office parks, and golf courses, lives one of the rarest snakes in Massachusetts: the northern copperhead.
One of only two species of venomous snakes in New England (the other being the bigger, better-known, and potentially more dangerous timber rattlesnake), copperheads in Massachusetts are listed by the state Division of Fisheries and Wildlife as endangered, and occur only as remnant populations in a few isolated locations in the Connecticut River Valley and, surprisingly, in the Blue Hills, a heavily used state park bordered by several Boston suburbs.
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"It's mind-boggling that there's still a population of these snakes that exists within the metropolitan Boston area," said Tom French, the division's assistant director for Natural Heritage and Endangered Species.
French said there are three known populations of copperheads in the state, two in Western Massachusetts and the third in the Blue Hills. He estimates there are only 150 to 200 copperheads left in Massachusetts, with about 50 of the snakes living in the Blue Hills.
"The Blue Hills is like an island in a sea of urban habitat," said French, "and the snakes are kind of stuck there. Because they don't have the mobility of birds and mammals, they have a hard time expanding into new areas, especially in a situation where they're surrounded by roads and buildings."
Educating the public about endangered species presents a dilemma for the agency's biologists. "On the one hand we don't want to tell people about them," said French, "but on the other hand we want people to realize they're here because they're unique and endangered."
Biologists at Natural Heritage and Endangered Species acknowledge that some of the known locations of copperhead populations are an "open secret." The Blue Hills Reservation website, for example, clearly states that copperheads and timber rattlesnakes, which are also endangered in Massachusetts, are found in the park.
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"On the one extreme, we're afraid of people possibly killing snakes like copperheads," said endangered species review biologist Misty-Anne Marold, "and on the other extreme we're afraid of the animals being loved to death by well-meaning people who just want to see them, but in the process may irritate them at their hibernaculum sites [places where snakes congregate to hibernate], expose them to disease, or just habituate them to people to the point where they're no longer afraid of humans."
Humans do remain the biggest threat to these animals, even within sanctuaries like the Blue Hills. Being accidentally run over by cars, habitat destruction, and outright killing are constant threats to the copperheads' survival.
"We lose four to six rattlesnakes and copperheads per year due to road mortality," said French. "They're killed by cars as they cross roads at night, especially on Chickatawbut Road," which traverses the Blue Hills in Quincy and Milton.
French said Natural Heritage has been pushing to close the road at night during the summer months, when copperheads and timber rattlers exhibit nocturnal behavior. Since 2009, the Department of Conservation and Recreation, which oversees the Blue Hills Reservation, has closed Chickatawbut Road from 8 p.m. on Saturday nights to 7 a.m. on Monday mornings during the summer as part of “Sundays in the Park,” which allows people to use the road for recreational activities such as walking and cycling. This summer the road is closed between Route 28 in Milton and Willard Street in Quincy on Sundays from June 17 through Sept. 3, according to a DCR press release.
In another possible threat to the endangered snakes, the city of Quincy has been seeking permission from the state to expand Pine Hill Cemetery, which borders the Blue Hills Reservation. According to a September 2011 article in the Quincy Patriot Ledger, the city is trying to expand the current 50-acre cemetery by adding 18 acres of wooded land that the city owns nearby. Because the proposed expansion includes possible copperhead and rattlesnake habitat, Natural Heritage would have to grant permission for the project to proceed.
French says projects like the proposed cemetery expansion keep "chipping away" at the edges of the park. "The continual expansion of the surrounding communities causes an ongoing shrinkage of this island of habitat," he said.
And then there's the issue of people killing snakes during chance encounters, or illegally collecting them.
"These snakes are rare in part because some people kill them, or collect them for monetary gain," French said.
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As an endangered species, copperheads in Massachusetts are protected by law under the Massachusetts Endangered Species Act, and it is illegal to collect, kill, possess, or harass them. Penalties include fines and jail time. French said it's even illegal to visit known hibernaculum sites.
Copperhead venom can cause significant tissue damage, although it is seldom life-threatening to a healthy adult.
Like other venomous snakes, the copperhead uses its venom primarily for hunting, delivering a lethal injection into a prey animal, such as a mouse. They will only bite humans or other large animals in self-defense.
French said there has been only one confirmed copperhead bite in Massachusetts in recent years, a DCR employee who was picking up brush in the western part of the state and got bitten on the hand.
As for natural threats, copperheads can be prey for other snakes, like black racers and milk snakes, as well as mammals such as coyotes and foxes. Black racers are common in the Blue Hills, and French said they' have been documented feeding on juvenile copperheads.
But the biggest natural threat comes from above.
"Hawks," said Chuck Smith, a biology professor from Wofford College in Spartanburg, S.C., who studied copperheads in Connecticut for his PhD dissertation. "Red-tailed hawks especially. When copperheads bask in open, rocky areas, they tend to stay at least partially hidden under vegetation to avoid being detected by hawks."
And copperheads don’t have to try too hard to stay hidden. Their cryptic coloration is a model of evolution. The snakes’ coppery brown color and hourglass markings blend in with the fallen leaves of the forest floor. “Most people probably walk right by them and never even know they’re there,” said Smith.
Surprisingly, even tree growth may have an adverse impact on copperheads by shading the rocky ledges where the snakes congregate and bask in the sun. Copperheads need forests to disperse into during the summer, but they also need open rocky areas with plenty of sun for their hibernacula. “Forests could be giving too much shade now on traditional basking sites,” said French. “We may have to cut back some of the trees around den sites.”
Copperheads denning in rocky terrain is a behavior that's unique to northern populations, explained French. "In the South, copperheads are found all over the place, and do not aggregate at den sites in specific habitat types like they do up here."
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French said the Blue Hills, with its numerous rocky outcroppings, provides good habitat for copperheads.
Smith said the copperheads' denning behavior in the Northeast is all about temperature. "They have to get below the frost line and within a place that has sufficient humidity that they won't dehydrate over winter."
Graham Reynolds, a herpetologist and post-doctoral research scientist in the biology department at the University of Massachusetts in Boston, said snakes like copperheads are a key part of the food chain, both as predators of smaller animals like rodents, and as food for larger mammals and birds of prey.
"As one of the most attractive species of snakes in North America, the loss of copperheads in Massachusetts would be a great loss to Bay State biodiversity. Here in Massachusetts, the last remaining populations of copperheads represent what little is left of our wild areas,'' said Reynolds.
Don Lyman can be reached at donald.lyman@merrimack.edu.