They first made landfall in North America several years ago on the balmy shores of Florida. And now they have spread, moving up through the continent and settling in the unstable Alberta climate. They're here and they're multiplying.

They are ... the doves.

(Iruka via Wikimedia Commons)

Well, Eurasian collared doves if we're being scientific about it.

"We counted 38 on this year's Christmas bird count, and really in two spots. One of them here in Forest Lawn and the other over in Dover," said Phil Cram, with the Calgary Christmas Bird Count.

"They have been spreading throughout southern Alberta for the last 13 years, since they first turned up."

(Iruka via Wikimedia Commons)

The story goes that the birds, originally from Asia and Europe, were introduced to the western hemisphere when they escaped some cages in the Bahamas during a pet shop burglary.

Their march has been relentless ever since, straddling vastly different climates and moving in on the turf of other birds — although pointedly avoiding the northeast corner of the continent.

(Iruka via Wikimedia Commons)

"Effectively, it's an invasive species," said Cram. "They are not considered to be particularly harmful to native species at this stage, given the numbers in which they exist, but potentially they could be down the road if they start to displace native species from their normal habitats."

According to the Cornell Lab of Ornithology, humans can take the blame for the success of the species. The birds are smart enough to linger in urban and suburban areas, where food from feeders is abundant.

(Iruka via Wikimedia Commons)

Cram isn't sure why the birds seem to be concentrated in a small area of Calgary's southeast, but he is sure that will change.

"This kind of habitat exists throughout the city, but once a pair establish here and have young and so on and so forth, that's how a little population will grow, and then from here they will undoubtedly radiate out," he said.

"So I would expect in 10 years time, we will be seeing hundreds of these on our Christmas bird count."