GRAFTON - A lot of barred owls are having a tough time in what is a banner year for the large night-hunting raptors.

Although there is a healthy population of birds, many are being hit by cars as they search after dark for their supper. Since Aug. 1, Tufts Wildlife Clinic at Tufts University's Cummings Veterinary Medical Center treated 85 barred owls, which are the third-largest owls of eight species regularly seen in Massachusetts. The current number in the clinic is 24, some of which may soon return to their natural habitat.

"A majority are being found on the side of the road, mainly by the general public," said Dr. Maureen Murray, assistant director of the wildlife clinic. "Our presumption is they are colliding with vehicles."

Dr. Murray said she wants people to realize that the possibility of hitting an owl is a common problem, not just with barred owls, but other species of birds, including red-tailed hawks. She said motorists traveling at night should slow down and keep an eye out for owls to avoid injuring them. The birds tend to hunt roads because mice will be visible when they are trying to cross or get at salt on the roads during winter. The birds swoop down at their prey and are hit by cars.

When the injured birds are brought to the clinic by those who find them, or by local police or animal control officers, the clinic learns that the birds were found on roadsides dazed or otherwise injured.

"We're seeing a range of injuries, including a number of broken bones and injuries to their eyes," she said.

The clinic treats a wide variety of birds and mammals in the hope of returning them to the wild. If the injuries to the owls are not too traumatic, and they can be restored to full capabilities, to where they can fly and hunt properly, they will be released. Many suffer such traumatic injuries that they have to be euthanized.

Dr. Murray said when the birds suffer blunt trauma, such as what happens when a bird hits a car, they can suffer both broken bones and eye damage. In November, a barred owl that was found in Sterling by Lisa Snow of Clinton, and her daughter Ella, 6, was brought to the clinic by Sterling police and the Sterling animal control officer Louis Massa. It is believed to have been hit by a car and it suffered eye damage. It is still being treated, but it has shown improvement and will have a good chance of getting returned to the wild.

"There are some ocular type of injuries that don't permanently affect their vision," Dr. Murray said.

Along with barred owls, the clinic has seen other types of injured owls, including great horned, northern saw-whet and eastern screech owls. Dr. Murray said they see a few snowy owls, but none so far this fall.

Thomas French, state Division of Fisheries and Wildlife assistant director for natural heritage and endangered species, said that although it is unfortunate for the birds that are being injured, it is an indication of a large population of barred owls this year.

"There is no more risk of them getting hit than ever, but there are more owls," he said.

Barred owls are the most common owls in the state, and they are large, between 16 and 25 inches in length. The large numbers may be in part due to increased numbers of their favorite prey, white-footed mice and other small mammals.

Mr. French said last year was a good year for acorns, and numbers of squirrels, chipmunks and mice are up. He said squirrels have been seen swimming in reservoirs to get to places where acorns can be found, and crossing roads in large numbers. There have even been complaints from Worcester Regional Airport that squirrels crossing the runway might draw hawks to fly down and interfere with airplanes.

Andrew Vitz, state ornithologist, said there are a lot of owls this year and many may have come down from the boreal forests of Canada.

"In one in five years we get irruptive movements," Mr. Vitz said, adding that there could be many young birds finding territories. "The last big movement was in 2013."

Mr. Vitz said it is most likely a result of low food resources in the owls' northern breeding areas, combined with good food resources here.

Barred owl numbers are up in general partly because former farms are growing up to forests. The owls tend to nest in cavities in forest trees. Other species are declining because they depend more on open fields to hunt.

"There are more (barred owls) today than there have been in decades," he said.