STRATHAM, N.H. (AP) — A group of mice is called a nest, but what do you call 1,000 of them in one animal shelter?

“Crippling,” said Lisa Dennison, executive director of the New Hampshire Society for the Prevention of Cruelty to Animals, which is scrambling to care for an overwhelming influx of rapidly reproducing rodents.

It all started Monday when a man arrived saying he wanted to give up 150 mice. But then he clarified: 150 containers of mice, not individual critters. He had 73 mice with him that day, and by Friday morning, about 450 had been transferred to the shelter. Another 500 or so were on the way.

And that number is growing thanks to some basic biology. Many of the mice arrived pregnant.

“One of the challenges is that the gestation is short and breeding begins early on,” said Dennison. “It’s an enormous problem. This is something that got out of control significantly.”

Part of the shelter’s cat pavilion has been turned into a mouse hospital and hotel, with dozens of containers lined up on the floor, resting atop multiple tables and stacked on shelves. It’s a lot of work for a facility that at most once took in 125 animals in one day.

“It does happen where you take a large number, but even when we took in 54 goats or we took in 39 cats, I mean, those are still large numbers, but much more manageable as you can imagine than hundreds and hundreds of mice,” Dennison said.

Other shelters have agreed to take some of the mice, and some are being sent to foster homes. At least four were adopted Friday.