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National Park Service officials on Wednesday reported finding a record number of mountain lion dens in the Santa Monica Mountains and Simi Hills during what they’re calling “a summer of kittens.”

Five mountain lions gave birth to a total of 13 kittens from May to August 2020, according to a statement from the Santa Monica Mountains National Recreation Area.

That’s a record number of dens within the time period during the officials’ 18-year-study of mountain lions in the area. The previous record, four dens found across 10 months, was reported in 2015.

Jeff Sikich, a wildlife biologist who has been studying the Santa Monica Mountains’ resident felines, called “this level of reproduction a great thing to see, especially since half of our mountains burned almost two years ago during the Woolsey Fire.”

Researchers visit the dens when the mother leaves to hunt for food, feed or rest, according to NPS.

Through telemetry, a biologist tracks her movement while others check up on the health of the kittens and tag them. The tags later help scientists identify the cats on webcam footage and when they’re captured to be fitted with radio collars.

Scientists found the first litter on May 14 after 4-year-old P-54 gave birth to three kittens, two males and one female.

The second den, with three female kittens by 10-year-old P-19, was discovered on June 19. Researchers believe it’s her fifth litter, after giving birth to four kittens back in 2018.

“Mountain lion mothers typically raise their offspring for about a year and a half, which likely means P-19 did not get much of a reprieve from kitten-raising before she became pregnant with her latest litter,” a statement from NPS said.

Scientists found the third den on July 6. P-65, a 3 1/2-year-old cat who survived the Woolsey Fire in November 2018, gave birth to one female and two male kittens. She has stayed within the burn area but tracking data shows her living in small unburned patches within the perimeter, according to NPS.

On July 7, NPS officials found P-67’s den of two kittens–one male and one female–in the Simi Hills. It’s only the second time NPS discovered a litter at the site, the first time being in 2018.

Finally, on Aug. 6, scientists found two female kittens by P-80. She had her litter within an unburned portion of the Woolsey Fire perimeter.

The scientists have been studying cougars in the 150,000-acre Santa Monica Mountains National Recreation Area in Ventura and L.A. counties to learn how the animals can survive “a fragmented and urbanized environment,” NPS said.

“It will be interesting to see how these kittens use the landscape in the coming years and navigate the many challenges, both natural and human-caused, they will face as they grow older and disperse,” Sikich said.