The first written account of Santa Claus having reindeer was in 1821, and since then most people have assumed the reindeer were male -- but a scientist says those people would be wrong.

Andrew Hebda, a zoologist at the Nova Scotia Museum, says while both male and female reindeer have antlers, only the females have their antlers during the winter months.

"Being members of the deer family, the males grow their antlers a little bit earlier and just after mating season, which is just about finished now, they drop off. So over a winter you'll never see a male with antlers," Hebda said.

Pregnant females use their antlers to dig through the snow in search for food, and lose them just before giving birth, he said.

It's most likely, he said, that Rudolph, Dasher, Dancer, Prancer, Vixen, Comet, Cupid, Donner and Blitzen are all female.

"Any reindeer right now with antlers is a girl," he said.

New focus has been placed on their gender in part because of a New York City Twitter user's assertion this month they are "a team of strong, powerful, underrated women."

The tweet, relying entirely on the antler theory of gender, proved very popular -- it has garnered more than 680,000 likes and more than 200,000 retweets.

A Chicago Zoological Society blog post echoes the contention that the antlers tell the tale.

"This isn't to say Santa only had female reindeer, but the nine flyers were girls," it said.

"Let's be honest, unlike Santa, reindeer don't live forever, so Santa needs both male and female reindeer, no? Because boy reindeer don't give birth to future generations of magical flying reindeer."

Hebda says there's another option -- castrated male reindeer don't lose their antlers.

"That's always a possibility. It's a question of whether Santa has followed a code of practice for proper raising of animals in castration is perhaps up in the air at the moment, but that's a possibility," Hebda said.

Hebda said European reindeer are cousins of the North American caribou. There have been some introductions of reindeer into North America -- most recently into Newfoundland, he said.

While Hebda can talk about reindeer gender, he's not prepared to explain how they fly.

And while many children leave milk and cookies out for Santa on Christmas Eve, Hebda said that's not a good choice for the reindeer.

And he said carrots may also be too rich of a treat to leave out for Santa's reindeer. He suggests lichens, leafy greens and dried mushrooms instead.