Tucson's Reid Park Zoo has four new lion cubs.
Zoo officials say the cubs were born in December.
A zoo keeper could hear at least one cub on the morning of Dec. 23. The next day, it was confirmed that five cubs were born, but one did not survive.
Officials say the mortality rate for cubs up to one year old is close to 30 percent in zoos, and it's significantly higher in the wild.
All four cubs are gaining weight, but the staff remains concerned about one male who has slow weight gain and appears weaker than the others.
Zoo Veterinarian Alexis Moreno says a litter of five cubs is unusual, and but she's cautiously optimistic.
The litter was born to lions Kaya and Shombay. It's their second litter.
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