Mobbing is a defensive behavior birds undertake to protect their nest or young from potential predators. Individual birds may go after another bird, mammal, snake, or even vehicle. But that’s not mobbing. True mobbing occurs when more than just the local male and/or female go after an intruder. Mobbing occu rs when other individuals from the neighborhood join the fray.
Wikipedia defines mobbing as, “… an assemblage of individuals around a potentially dangerous predator.” So, the attached photo by Ken Miracle of a Cooper’s hawk going after a turkey vulture and by Ceredig Roberts of a red-winged blackbird chasing a golden eagle, qualify as nest defense, but not mobbing. And while we’re at it, the turkey vulture is not a predator, but it sure looks like a predator! That’s all the mobsters care about — what you look like.
Mobbing occurs most frequently, or perhaps just most obviously, in birds. But other species do it. Humpback whales mob killer whales, bluegills mob snapping turtles, and meerkats mob snakes and foxes, to list a few other examples.
This topic bubbled up in my mind in early June when I came upon a sandhill crane in a remote meadow being mobbed by red-winged blackbirds. Three male blackbirds and one female repeatedly dove upon the crane, which was peacefully foraging in the meadow. They not only swooped at the crane, but also pecked the back of the crane and landed on it! The crane barely paid any attention to the attack, simply dodging a few shots at its head.
After a few minutes, the crane had wandered off far enough that the blackbirds stopped mobbing and returned to their perches on the edge of the meadow. I say the sandhill was “peacefully” foraging but make no mistake. If that modern-day dinosaur had found young blackbirds just out of the nest, it would have readily gobbled them up. But the crane was not looking for blackbird nests. It was searching the ground in the grasses and sedges of the meadow. Red-wings don’t build their nests there.
Red-winged blackbirds are always on guard during the nesting season. If you walk at Hyatt Lakes, bike the Greenbelt, or play disc golf at the east end of Ann Morrison, for example, you have had blackbirds flying over your head and diving at you.
Another blackbird even more apt to go after a predator in groups is Brewer’s blackbird. This species also likes wet habitats, although not the riparian zones and cattail marshes preferred by red-wings. They’re also “wilder” and not usually found in areas with heavy human presence.
My latest experience with this species was at Sheldon National Wildlife Refuge in Nevada. I was camping at a remote spring site which always has Brewer’s blackbirds during the nesting season. As I walked up a two-track to the spring, a number of blackbirds began flying overhead and giving “chuck” notes. By chance, I spotted a nest with a female on it, just off the edge of the track in the top of a large Great Basin sagebrush plant. She left the nest, and 11 blackbirds then assembled to harass me. At least five of the birds flew in from a nearby area to join the mob. Only one of the birds was a female. The other females were probably sitting tight on their nests while the males joined forces to defend that particular nest. Good neighbors.
Brewer’s blackbirds also go after cats. I’ve had first-hand experience and have also seen videos of Brewer’s diving at cats and hitting them in the back to keep them moving away from a nest area. I bet fox, coyotes, bobcats, badgers, and any other ground-based predator get the same treatment out in the boondocks.
Later in the day I had watched red-wings mob the sandhill, I witnessed a much more common type of mobbing. Seven western kingbirds were “encouraging” a red-tailed hawk to keep moving. The hawk was just cruising from one place to another but apparently happened to pass by a tree where migrating kingbirds were perching. No kingbird of any species (there are seven species regularly occurring in the U.S.) will put up with a potential predator. They seem to chase them no matter where they are or what time of year it is.
In some cases, the mob and the mobbed are the same species. I have often seen American crows mob red-tailed hawks. I’ve equally often seen red-winged blackbirds mob crows. Common ravens will mob golden eagles, and then themselves get mobbed by kingbirds. Chickadees mob jays and jays mob red-tails. There are many more examples. The rule seems to be, “if it’s bigger than me, and looks like a predator, go after it.”
Yet this rule doesn’t seem to apply to most bird species. I could give you a long list of Idaho birds I’ve never seen mob a potential predator. But just because I’ve not seen it doesn’t mean it doesn’t happen. The examples above apply to species which are out in the open and/or not at all secretive. One wonders if super skulky species also mob. What about my favorite bird, the yellow-breasted chat? How about house wrens or song sparrows? Do they gang up on a sharp-shinned hawk searching the undergrowth? How about a screech-owl or a snake?
I’m sure a search of the scientific literature would reveal a lot more. One hypothesis is that social species will be more apt to mob than solitary species. Of course, the path from social to solitary is a continuum, so you would have to come up with a measure of “sociality.”
Another window on mobbing behavior is how species respond to the playback of owl calls. One way to get birds around you to show themselves is to imitate a pygmy-owl. The simple tooting of these owls often draws the attention of small birds you otherwise did not know were in the vegetation. The tooting patterns of the northern pygmy-owl in Idaho and the ferruginous pygmy-owl in the Southwest are different, but they are both easy for a human to imitate. There are 27 other species in this group and learning the pattern of the local call is a good first step in finding new birds in a new country.
Imitating a pygmy-owl does not always work. But sometimes it works extremely well. I recall one time in Brazil when my tooting brought out the usual array of finches, spinetails, and little flycatchers. Then, a relatively large dark-billed cuckoo flew in. What was it up to? Perhaps it had a nest nearby. Or maybe it was going to try to grab one of the other little mobbers.
I wrote in an earlier piece how we once used a pygmy-owl call to try to find a rare warbler in Oaxaca, Mexico. All we got were a bunch more pygmy-owls! We couldn’t find another bird of any kind until we left the area. Way too many owls.
But my favorite mobbing experience was due to a real ferruginous pygmy-owl in Veracruz, Mexico. I was watching several species of hummingbirds in a large patch of dense, flowering shrubs, trying to identify the females as well as the more obvious males. I suspected there were at least two dozen hummingbirds in the patch.
Suddenly, a pygmy-owl flew into a small tree that emerged from the middle of the shrubs. As many as a hundred hummingbirds arose from the vegetation to mob the owl. It sounded and looked like a huge swarm of bees! The owl only stayed for a few seconds before beating it out of there!
In addition to the species I’ve mentioned, gulls and terns are also well-known mobbers. They nest in dense colonies, and researchers trying to study them must be prepared for the constant onslaught the colony will bring to the curious. But they can also be on the receiving end. I once watched a Forster’s tern peacefully flying low down the edge of a small canal in eastern Oregon. As it passed the territory of a red-winged blackbird, a male blackbird stormed out of the vegetation and bopped the tern on the back of the head. The tern was clearly caught unawares, swerved violently to regain its bearings, and looked back over its shoulder as if to ask, “what the heck?!”
Mobbing and simple nest defense is entertaining to watch, and it seems no animal is actually hurt in the end. But when birds are mobbing you, or a pair are defending their nest, realize they are just trying to protect their young. Keep moving and appreciate how important young life is, even to birds.