Once the cubs die, a biological signal sends the females back into fertility. Infanticide allows the newcomer to focus his energy on fathering his own cubs before he too becomes sick, wounded or old, then loses control of the pride to yet another interloper.
However, People for the Ethical Treatment of Animals and others have questioned the ethics of culling cubs.
"Like domesticated cats, big cats breed, unless you make sure that they are sterilized, and that is exactly what the zoo had an ethical obligation to do, rather than bringing cubs into the world simply to bump them off," a PETA spokesperson said in the Daily Mail.
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Last month, the Copenhagen Zoo attracted similar criticism for killing Marius the giraffe, dissecting him in public and feeding him to lions. The zoo killed Marius because he had a common pedigree. The zoo couldn't use him as a stud because he as too related to other giraffes in captivity, nor did the zoo want to pay for the upkeep of a genetically-useless giraffe.