Lemmings and voles are cyclical, like many rodents, Their populations fluctuate according to food abundance. It typically works like this; A relatively small rodent population feels heavy pressure from the local predators, however there tends to be an abundance of edible vegetation. The rodents breed prolifically and soon overwhelm the predators by sheer force of numbers. Predator populations rise along with the rodents, lagging behind by a year or two.
The rodent populations stay ahead of predator populations because they reproduce faster than the predators can eat them. The local vegetation cannot keep up with rodent populations and every five or so years the rodents start to go hungry.
Lemmings especially are known for forming large groups that move out, looking for something to eat. The predators have an orgy of feasting on lemmings until the lemming population crashes. Followed by a crash in predator populations a short time later.
The pressure on the local vegetation is lifted and there is a short period of luxuriant plant growth. The cycle starts over. Similar cycles happen all over the world but they are easily recognized in the far North.
Predators often do what the lemmings tried to do, they disperse to new areas in search of food. Raptors have the advantage of flight, so they can travel much farther than four legged predators.
These photos of two different Snowy Owls were taken in Cape Cod, Massachusetts, by Gary's brother Doug Lyons. He is a much better photographer than Gary is. His superior camera equipment surely has a lot to do with that.
Right now there is an owl invasion into the Northeastern USA.
This heavily marked individual is a sub-adult female.
The same individual. The top two photos are of an adult female. Males tend to be all white with few markings or none at all. Many of the owls that head south on invasion years do not survive the journey. Hopefully these owls will make it.
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