It’s a little-known downfall of the carefree summer months: The number of cats and dogs in the city’s shelters tends to spike in June, July and August.

Animal shelters in the city are taking in their usual summer influx of homeless pets, including large numbers of young kittens.

“There is no better time to adopt,” said Gail Buchwald, senior vice president of the ASPCA’s adoption center.

This year has seen an increased number of animals at the shelter: Through July of this year, the ASPCA has taken in 865 kittens, a 21 percent increase from the same time last summer, when they took in 717 kittens.

She explained that cats begin to mate around April or May, and that they typically give birth during the summer months. People often give the kittens to shelters rather than letting them run wild on the streets.

Many pet owners, however, are not prepared for the time and expense needed to raise these offspring, according to Buchwald.

“Generally, it’s much more than folks anticipate, and for that reason the litters get relinquished to shelters,” she said.

Animal shelters also become more crowded in summer because so many people move in June, July or August. Oftentimes, their new landlords either limit the size of pets or ban them altogether, Buchwald said.

“Moving is the number one reason for pet relinquishment across the country, and New York City is no exception,” she said.

About 50,000 homeless pets end up in the city’s shelters and rescue groups each year, according to Buchwald.

She said that with a live release rate of 70-75 percent, New York is one of the best cities in the country at avoiding euthanasia. Nonetheless, that rate could improve even further with more government resources, she said.

Keep your cat indoors, ASPCA says

Outdoor cats kill hundreds of millions of songbirds and small mammals every year in the United States, and are at high risk for getting hit by cars and contracting disease. As a result, the ASPCA advises that all cats be kept indoors. For many of the same reasons, it recommends that dogs stay leashed except in certain designated areas like dog runs.