(CNN) A lioness at a German zoo has killed and eaten her two newborn cubs just days after giving birth, to the horror of her keepers.

Kigali, a first time mother, gave birth to two cubs at Leipzig Zoo in Germany on Friday, the first lions to be born there in 15 years. Maria Saegebarth, a spokesperson for the zoo, told CNN that the lioness initially took good care of the cubs.

On Monday evening, however, while grooming the newborns, Kigali killed and ate them. She displayed no unusual behavior before eating her cubs, Saegebarth said, and had been eating normally throughout the day.

The zoo announced the deaths in a post on its Facebook page, saying staff were "shocked and sad" at the turn of events. Kigali would soon be returned from the maternal area to the main enclosure, where she would be reunited with Majo, the cubs' father, it added.

Leipzig Zoo in Germany, where lioness Kigali killed her newborn cubs.

Because Kigali ate the cubs in their entirety, an autopsy cannot be performed on them to determine whether they were ill, which may have triggered their mother's actions, Leipzig Zoo said. "This is a kind of natural behavior as it happens in nature, too," Saegebarth told CNN.

Maren Huck, a lecturer in animal behavioral ecology at the University of Derby in the UK, told CNN that lionesses did sometimes eat their cubs in the wild, although it was a more frequent occurrence in captivity.

It also occurred in other species, such as domestic cats, with first time mothers more likely to eat their infants.

"If the cubs themselves behave strangely, that might be a reason for animals to eat their offspring," Huck told CNN, citing illness or developmental issues as possible causes. "If their infant doesn't respond as an infant should do, it's not recognized as an infant and therefore the maternal instinct doesn't kick in."

"It is more likely in captivity because there are more factors that would contribute. It is well known that if animals in captivity are stressed, they are more likely to eat their cubs," Huck explained. "On the other hand, they're less likely to be malnourished in a zoo. In the wild, if a female isn't fit enough herself, she is more likely to eat her cubs."

She stressed that the death of Kigali's cubs does not necessarily indicate animal welfare issues at Leipzig Zoo, adding that zoos in general had improved their conditions.

"They would have to check carefully whether it happens again, particularly whether the same female does it again," Huck said. "If it doesn't happen again, it's more likely due to inexperience of the mother, or health problems in the infant."