Snowy Owls head south this winter
Snowy owls (Bubo scandiacus) will often come south in unpredictable invasions known as ‘irruptions.’ It’s mostly about food and babies, but scientists still have a lot to learn about this phenomenon – and this winter’s is the biggest in decades!*
It has long been assumed that the irruption of Snowy owls in the southern portion of North America was the result of a harsh arctic environment with less abundant food sources, forcing these magnificent and charismatic birds to move elsewhere for foraging. It seems we had it all wrong! Abundant prey in the Arctic environment helps the Snowy owls produce even more eggs hence a larger brood per couple. All these young owls are just too numerous for their local environment and will eventually have to disperse geographically and head south. The young birds that arrive at our latitude are not famished individuals, but owls with a good body mass and abundant fat stores. This movement of Snowy owls is somewhat normal, taking into account that they will not systematically use the same reproduction site every year but will rather move around depending on prey abundance. We also know with tracking studies that the individuals that go south are the young ones, the adult females usually staying put up north. Abundance in the lemming population in the eastern Arctic will apparently drive the movement of young Snowy owls towards Québec, the Maritimes and the northeastern USA, as is the case this year, or more towards the Prairies if the lemmings were more numerous in the Northwest Territories.
Smaller irruptions happen every few years, but once or twice in a lifetime a very large irruption occurs, when snowy owls show up much farther south, and in much greater number than usual. This winter, 2013-14, is one such extraordinary event, the largest irruption in the Northeast and Great Lakes regions in four or five decades. The irruption zone stretches from Minnesota to Newfoundland, with Snowy owls having been reported as far south as Florida and Arkansas, and even on Bermuda.*
Since November of last year up to now, numerous Snowy owls have also been sighted by birders all over the southern portion of Québec. Individuals have even been seen along the coast of France or in Belgium! Although these birds did not fly all the way there and probably took advantage of a cargo boat at some point, these sightings are most likely a result of this phenomenon.
It is difficult to determine how well the individuals that are displaced to more southerly latitudes fare. However, during these irruptions it is common for a small number of the snowy owls to be submitted to the Canadian Cooperative Wildlife Health Centre for autopsy. In these cases, the majority are emaciated and this is probably the result of starvation. Electrocution is another common finding in these emaciated birds, and it might be that their debilitated physical condition predisposed them to electrocution because they are unable to avoid contact with powerlines. Lastly, a few of the emaciated birds succumb to secondary disease problems such as fungal infections. These findings seem inconsistent with the owls that have been examined in Québec so far this year with the majority of them having abundant fat stores and injuries due to trauma. The CCWHC would like to continue monitoring the health of these northern visitors so please consider submitting any sick or dead snowy owls to your nearest CCWHC Regional Office. It is important to note that artificial feeding is not helpful for these birds and likely does more harm than good, (see article about Feeding Wildlife).
This abundance of Snowy owls has created problems for airports in large North American cities such as Montréal, New York, Boston or Philadelphia. These owls will often appreciate foraging for prey around airports which have a landscape very similar to their usual hunting grounds in the arctic. For obvious security reasons, numerous individuals had to be captured and relocated since the start of this irruption.
An interesting research project was developed quite rapidly at the end of last year to take advantage of this large irruption of Snowy owls down south in North America. Called Project SnowStorm, its aim is to better understand the population dynamics of this arctic avian species and what drives this irruptive phenomenon. This project is a result of collaborative efforts between autonomous researchers, biologists, veterinarians, some state wildlife agencies and research groups such as OwlNet, Hawk Mountain Sanctuary and the Maryland Zoo in Baltimore. If you want to know more about the project or want to get involved, please consult their website. http://www.projectsnowstorm.org/
Article by André Dallaire with excerpts (*) from http://www.projectsnowstorm.org/
For more information, please visit: http://ebird.org/content/ebird/news/gotsnowies2013/