The first time most people hear the word, "irruption", they tend to conflate it with a similar-sounding word and visions of volcanoes and hot lava erupt into their minds.
But the word "irruption" describes a different sort of explosive event: it applies to a sudden, sharp and unpredictable increase in the relative numbers of a population. Irruptions can be triggered by the search for food or other resources, or by weather conditions. Currently, it applies to the situation that birders have been seeing this winter, where hundreds of snowy owls, Bubo scandiacus, have flooded south from the Arctic in search of food.
Snowy owls aren't the only species that irrupt, but they are amongst the most visible due to their large size, distinctive colouring and the fact that they tend to sit in plain view alongside roadways, in open fields and at airports.
When they are not breeding, snowy owls are wanderers by nature. They roam widely around the Arctic in search of their favourite prey, lemmings. So when lemming populations crash in the far north, the owls simply wander farther than they usually do in search of rodents (or sometimes ducks) to prey upon. Since lemming populations increase dramatically before a crash, snowy owl parents can feed and raise more of their young until independence than usual, so the owl population also increases. When lemming populations inevitably crash, there are more snowy owls than usual, and they all are competing for the same resources. The younger and less experienced birds tend to lose out to their more experienced elders, so the younger birds expand their search for food: they move south.
Almost none of these irrupting owls have ever seen a human being, so they tend to be unafraid of us, often allowing people to approach quite close to them. And this can cause problems for the birds.
This lovely video, produced by multi-award-winning videographer Bob Sacha and featuring the work and wisdom of photographer Paul Bannick, explains the issues.
"The owl is truly a messenger, and in an irruption, the messenger comes to us", says wildlife photographer Paul Bannick in the video, below.
"It's our challenge to get that message and do something about it: we are stewards of more than just our back yard."
[Reading on a mobile device? Here's the video link]
Filmed in Ontario, Canada.
.. .. .. .. .. .. .. .. .. .. ..