For the Birds Radio Program: Protecting Babies
Why do redwings chase crows? 3:48
This time of year, on just about any drive through the countryside, just about anywhere in the Northland, you can look up and see Red-winged Blackbirds chasing crows. The obvious question is, “Why?”
Most of the year, redwings and crows pretty much ignore each other. But when redwings start nesting, crows start paying attention. Crows are opportunistic omnivores who need meat, especially during the breeding season. Females need to replace the loss of calcium and protein they used up laying 4–6 eggs. Parents of both sexes need extra nourishment for the energy-intensive task of feeding three or four fast-growing babies. A modern crow’s main supply of meat comes from road kills—between rushing cars it can take quick bites at fast food that wasn’t quite fast enough. But during the nesting season, a rich supply of extra meat and fresh eggs becomes available right when a crow needs it most. All it has to do is discover a smaller bird’s nest and voila! A full day of fine eating. A redwing nest is substantial enough to support a crow while it snatches up the babies, and the nestful of baby redwings is richer fare than a nestful from a tinier species. The only trick is sneaking up to the nest without the adult birds noticing and inflicting damage.
So redwings have a lot at stake when a crow flies over their nesting areas in summer. To keep the crow’s attention away from their nests, the redwings chase off any crows within sight. Usually one lone redwing won’t actually strike the crow. A mid-air collision would be too dangerous for the blackbird’s fragile bones. But by keeping the crow’s attention engaged by simply annoying it, the redwing keeps the crow’s attention away from its nest. Ornithologists call this kind of behavior a distraction display. Because redwings usually have many territories in a small area, you can often see three or more of them ganging up on a single crow. That’s called mobbing. But a lone redwing doesn’t depend upon the security of numbers. He’s perfectly willing to tackle the crow by himself.
Redwings aren’t the only birds that protect their eggs and young by attacking potential predators to distract them. Robins also attack crows, though the robins usually wait until the crow approaches dangerously close to their nests. And all kinds of little birds attack jays. Blue Jays have to be pretty close to a nest to elicit attack by warblers, sparrows, and vireos. Blue Jays eat a lot of vegetable matter, even during the breeding season, and they only raid nests when the opportunity is really ripe. That’s why they can afford to have such conspicuous plumage and such noisy habits. Their relative the Gray Jay is a primary predator of eggs and baby birds, and littler birds know it. It’s almost impossible to see a Gray Jay in the woods in summer without several warblers and vireos hot on its tail. In summer, Gray Jays are skulkers, quietly moving about searching for eggs and nestlings, and their subdued plumage and silent flight aid them. Little forest birds are as much on the alert for Gray Jays as open country redwings are for crows. But whether you’re talking about the crows and jays or the redwings and warblers, Walt Disney was right–“It’s Tough to Be a Bird.”