The local squirrels use the top horizontals of the back fence as a run. Lately, the young squirrels have been particularly active, raiding the bird feeders and any other sources of food, even gnawing through the plastic to get at seeds or nuts. But they don’t have it all their own way. Over the last week, I’ve observed sparrows ‘dive-bombing’ the squirrels and chasing them along the fence. Even when the squirrel reverses direction the sparrow continues to harry it along, flying at its back as the squirrel runs and makes no effort to defend itself.
I was surprised, but I’ve observed it too many times to be doubtful. I would not have thought that a tiny sparrow would take on a squirrel, which must be several times its size, yet they quite clearly do. A few times there were several birds harassing the squirrel and chattering loudly, but sometimes it’s been a lone female or male. Good for them, say I!
I’ve heard that squirrels will take eggs and chicks so that probably explains the sparrow’s aggression. Squirrels may look cute but they are an invasive nuisance and classed as vermin. They destroy our native trees and shrubs and have driven our own lovely red squirrel to the brink of extinction (not to mention the toll they take on native birds and mammals). Sadly, this is very often the case when foreign species are introduced to a new habitat. There are many thousands of examples of the disruption (and often complete destruction) of native ecosystems by invasive species. Ecosystems evolve their balances over long periods and cannot adapt quickly to the sudden and large-scale introduction of new species. Such introductions are almost always to the severe detriment of established species and systems, particularly when, as in the case of squirrels, the invader carries pathogens (or memes) against which the native ecology has no defence.
Anyone who takes an interest in the natural world and is keen to learn from it might well want to consider these lessons and their applicability to the human world.