It was another grey and nearly drippy day as I headed out the door this morning with the dog in tow (some mornings he isn’t any more eager to go out than I). It had rained overnight, so everything was damp, but at the moment the air was still and relatively dry.
Up ahead I watched a largish raptor swoop up and land on a street light. I pondered the species for a moment, taking note of size and coloration as best I could with the animal backlit against the morning sky. It was about then that I noticed that the background chatter of morning birds was getting progressively louder.
Caw! Caw! Caw!
Crows. Lots of crows. Crows upon crows.
The hawk started to get a bit fidgety, and as the crows approached, it flew off, black-feathered shadows in hot pursuit. As it winged its way past me, I took note of the long, narrow tail, and its size as being generally larger than the crows. I guessed it was a goshawk, my second one in five days.
The hawk flew off westward, toward Goodnow Mountain, and no fewer than twenty-four crows followed in its wake, each calling with gusto. It was a mob scene if ever there was one.
Mobbing is a behavior we most often associate with birds, namely those that live rather colonial lifestyles: crows, gulls, swallows. It is believed that mobbing developed as a means to protect the colony by driving off predators. Safety in numbers and all that.
Most predators employ stealth in some form as a means of securing prey. Stealth requires quiet and concentration. It’s hard to concentrate when the air is full of raucous calls, and all chance of surprise is lost when twenty or so birds turn their noisy attention on you.
Not all mobbing takes place when an actual hunt is discovered. Sometimes the hunter (say, an owl) just happens to be in the neighborhood, trying to catch some sleep. If a crow spots a snoozing owl, that owl can pretty much forget getting any sleep. The crow brings in a few buddies, and before you know it, the poor owl is surrounded by loud and persistent calls. If it is particularly unlucky, the owl may actually be physically attacked by the crows. Eventually the harassment pays off for the corvids and the owl departs, looking for somewhere else to nap.
I recall as a child watching the barn swallows engage in mobbing behavior at my grandparents’ house. Usually they barnstormed the cat as she tip-toed across the lawn, but once in a while they would dive bomb us grandkids. It can be a scary event for kids, to have birds fly at their heads. Even if those birds are small, they are armed with sharp little beaks. Luckily, it didn’t negatively impact my love of the outdoors.
Mobbing behavior isn’t limited to birds. Bluegill sunfish have been studied attaching snapping turtles en masse (and I suspect they will go after swimmers’ toes as well). Meerkats and California ground squirrels use group tactics to drive off unwanted predators. Even ants will gang up on predators attacking their docile aphid herds.
So, keep your eyes and ears open. Now is a great time of year to watch for mobbing behavior because as the leaves fall from the trees, winged predators are more easily seen as they try to seek refuge in the soon-to-be-skeletal forest.
Photo: Large flock of Crows, courtesy EPA.