DENVER -- The Denver Zoo is celebrating the birth of four red pandas born last month.

The four cubs -- three male, one female -- were born on July 9 to Sophia, who is from Roanoke, Va.'s Mill Mountain Zoo and He-Ping, who arrived at the zoo in 2007 from the Milwaukee Zoo.

Red panda quadruplets are rare -- it's only happened four times in zoos in the past, according to the Denver Zoo.

The pandas, or firefoxes, were weighed and got a checkup on Thursday.

Red pandas are relatives of the giant panda, but they only grow to the sizes of a house cat. They are native to the Himalayas, where there are an estimated 2,500 living in the wild.

Red pandas are well adapted with their thick fur coats to live in the often low temperatures of the mountains of southeastern Asia and are quite comfortable outside during cooler days here in Denver. Their diet consists primarily of bamboo.

The cubs will be vaccinated and given the opportunity to grow and develop before venturing out onto exhibit for public viewing in the fall.

He-Ping and Sophia were paired together under recommendation of the Association of Zoos and Aquariums' Species Survival Plan, which ensures healthy populations and genetic diversity among zoo animals. Fortunately, the couple has proved to be an excellent match. In addition to the new quadruplet cubs, Sophia gave birth to twins during the summer of 2008.