Question: We heard a commotion this morning, lots of crows and a Red-shouldered Hawk. They flew close enough to count and we had 26 American Crows, all harassing one Red-shouldered Hawk! I wondered why so many crows were ganging up on this individual hawk. I know it’s normal, but that many? – Anonymous birder
Answer: What an interesting observation!
First, mobbing crowds with this large number are not uncommon. One observer L. Kilham once counted 136 crows mobbing a Great Horned Owl in Texas. When not nesting crows gather in nighttime roosts ranging from around 100 birds up to a roost of 2 million crows (am I glad I don’t live near that!). So, seeing this many crows together is not too surprising.
Crows mob a whole host of species. Birds of the World says,
“Species mobbed include Sharp-shinned Hawk, Cooper’s Hawk, Black Vulture (Coragyps atratus), Turkey Vulture, Bald Eagle, Crested Caracara (Caracara cheriway), American Kestrel (Falco sparverius), Barred Owl, Great Horned Owl, Common Raven, Blue Jay. Also mobs humans, raccoon, gray squirrel (Sciurus carolinensis), fox squirrel (S. niger), red fox (Vulpes vulpes), and domestic cat.”
Of course, that leads to the question of why? Note that all of the above are potential predators. Mobbing a potential predator is actually very common in the bird world and is not restricted to crows. I have even seen a Ruby-throated Hummingbird attack a Red-tailed Hawk (not that the hawk, as it moseyed away, even knew the hummingbird was stabbing at its tail feathers). But, for your question, let us focus on crows.
Konrad Lorenz in his book King Solomon’s Ring (1952) recalls an experience where he learned that for Jackdaws, the mobbing behavior cobbles together instinct, experience, and mimicry. The basic story is that after swimming Lorenz stuffed a wet black bathing suit into his pocket. While tending his pet Jackdaws (a European species closely related to crows), he realized the suit was soaking his pants and making him uncomfortable, so he removed it from his pocket. The pet Jackdaw saw the limp black object and attacked Lorenz’s hand instinctively. Lorenze inferred that the Jackdaw is hard wired to attack anything that carried a limp black object, the Jackdaw needed no training. After three such experiences, the Jackdaw no longer needed to see the limp black object before it attacked the hand. Subsequent generations of Jackdaws were taught to attack the hand without provocation.
In 1974, David P. Barash, University of Washington decided to test Lorenz’s observation. He conducted a study where he presented the local crows with a stuffed Great Horned Owl. Some of the times the owl held in its talons a stuffed crow. In others it held a black cloth. In the third series, the owl had nothing in its talons. He learned that the crows consistently attacked the owl, but whenever the owl held a stuff crow or the black cloth, the attack was more vigorous and vocal. His discovery
“…supports Lorenz’s contention that the presence of a black object stimulates corvid aggressiveness towards potential predators although is does not examine the supposed innateness of that behavior. The significantly heightened intensity of mobbing elicited by both the owl-crow and owl-cloth models in comparison with the owl model alone, combined with the similarity of response to the owl-crow and owl-cloth models, suggests that a simple “releasing mechanism,” whether innate or learned, is involved.”
Lesson for birders: When you hear crows freaking out, don’t ignore them, look to see if you can find the predator they may be mobbing.
References
Behavior – American Crow – Corvus brachyrhynchos – Birds of the World
Konrad Lorenz (1961) King Solomon’s Ring Translated by Marjorie Kerr Wilson. Methuen, London. 202 pages
https://sora.unm.edu/sites/default/files/journals/condor Departments of Psychology and Zoology, University of Washington, Seattle, Washington 98190. Accepted for publication 27 August 1974.
Answer by: Robert Mercer
SIB 