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The Nature Nut

Rosamund Pojar

Just last week a friend told me about great excitement at her place as she watched two northern flickers together with two black-billed magpies harassing a pine marten that was stealing the fat from the bird feeder. Not only did the birds mob the marten, but they followed it as it took off away from the feeder.

She was surprised that the two different bird species, who are normally not great friends, would act together and that they followed the marten.

This activity, called mobbing, is a commonly seen behaviour in some birds. Large groups of small songbirds of many different species (chickadees, nuthatches, sparrows) will suddenly group together with constant circling, diving and calling at a predator such as an owl or small hawk.

When I see crows, blackbirds, starlings and even ravens diving at something in a tree, I know that there must be some large hawk or a bald eagle sitting in the tree (or maybe a mammalian predator).

On the surface, this might seem counterproductive in terms of natural selection. After all, the smaller birds could easily be attacked and killed by the predator, preventing them from producing offspring and reducing the evolutionary “fitness” of the species.

Also, why would one species want to help another when they may both be interested in the same food at a feeder? Well, there is safety in numbers.

There also appears to be an element of altruism,  as well as, self-protection involved. It may be only one bird that raises the alarm, but that alarm alerts all the others of its own group as well as any other species that may feel threatened.

This mobbing behaviour is designed to harass the predator so much that it gets confused or frustrated and eventually leaves the scene — exactly what the mobbing birds want it to do.

Chasing the predator as it leaves, as seen in the case of the pine marten mobbing, also makes sense because it is much better to know where the enemy is than not.

Keeping the predator in view means less likelihood of being caught unawares.