Massachusetts schools are used to snow delays. But a bear delay?

This week Arlington Public Schools were delayed one hour when a black bear was spotted roaming around town.

“I totally understand they’re not used to seeing bears. Just like if it snows down South, everyone closes the schools. ... But we see bears all the time here in Hancock [New Hampshire], and I don't think we'd ever close the school — unless the bear was, like, sitting on the playground,” naturalist Sy Montgomery told Boston Public Radio on Wednesday.

Black bears have been well established in Western Massachusetts for decades, but have progressively been moving eastward into more densely populated towns like Arlington, according to the Massachusetts Division of Fisheries and Wildlife. In the 1970s, there were only about100 black bears in Massachusetts. Now, that number is about 4,500 bears.

As bears adapt to more urban and suburban habitats, human-bear interactions are increasing.

“Generally, bears don't want to see us that much,” Montgomery said, “but we're everywhere.”

For tips on how to keep ursine visitors out of your yard, watch this video from GBH News’ Curiosity Desk.

And the Arlington school delay was not the only surprise bear sighting this week. In Florida, a cub shocked beachgoers when it swam into shore.

“[Bears] frequently use that way of locomoting to get around,” said Montgomery. “They can swim, and they're strong swimmers. And when you think of it — polar bears are considered marine mammals, like whales, because they swim so much.”

In fact, bears are related to seals and dogs, both animals that can swim.

“If you look at their noses you can see how similar these animals are,” Montgomery said. And the Arlington school delay was not the only surprise bear sighting this week. In Florida, a young black bear shocked beachgoers when it swam into shore.

“[Bears] frequently use that way of locomoting to get around,” said Montgomery. “They can swim, and they're strong swimmers. And when you think of it — polar bears are considered marine mammals, like whales, because they swim so much.”

In fact, bears are related to seals and dogs, both animals that can swim.

“If you look at their noses you can see how similar these animals are,” Montgomery said.