Only a month old and already in a bad mood, a baby white rhino conceived through artificial insemination is delighting keepers at a Spanish zoo.

The male rhino was born in late April and unveiled this week, and is only the third in the world to be conceived with that technique, zoo veterinarian Enrique Saez said Thursday. The other two were in Budapest, Hungary, over the past two years.

The animal weighed about 140 pounds (65 kilograms) at birth and now tips the scales at 220 pounds (100 kilograms). Its mother, named Marina, gave birth after a 509-day pregnancy.

Artificial insemination is rarely attempted on rhinos because females in captivity do not ovulate well. But hormone tests on Marina showed she was in fact producing eggs, so vets decided to give it a try.

"She was an ideal candidate," Saez told The Associated Press.

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The baby is adapting well and last week even charged at keepers in its pen when the mother was taken away briefly to be inseminated again, forcing them to scurry for cover behind a wooden barrier.

"He is showing he is a male with character and a bad temper," Saez said. "That is a good sign."

The baby has yet to be named. The zoo plans to hold a contest asking the people of Madrid to choose between Cronos and Olimpo.

Those two Greek options were picked because the rhino was born right before a visit by International Olympic Committee officials, who evaluated Madrid's bid to stage the 2016 Games.

For now, the baby is mostly being kept away from its father — an aging guy that was never given a name — so it can bond with the mother.