Acting in defense

On a spring day last year I was jogging along the Fox River bike trail when I heard a red-winged blackbird’s warning call, which is a piercing single-note whistle. He was perched on a low branch of a tree along the trail up ahead and, as I approached, his calls became more frequent and insistent. Living near a river, I see and hear many of these these birds regularly, so I didn’t think anything of it. This time I was in for a surprise. When I reached the tree, he took off but then swooped down and flew right in front of my face before coming back and making contact with the top of my head. Fortunately, I was uninjured, but I picked up my pace to leave the area quickly. While the incident didn’t spark the kind of terror the denizens of Bodega Bay experienced in Hitchcock’s 1963 film The Birds, it was disconcerting nonetheless. Ever since that day, I’ve worn a hat when I go jogging in the spring and summer.

I didn’t blame the blackbird. He was simply doing his all-important job of protecting his nest. Red-winged blackbirds often build their nest close to the ground in marsh vegetation, shrubs, or trees near water, so I could easily have been too close for comfort as I passed by. These birds, which are widespread and not shy about nesting near where humans live, including in urban areas, have become well known for aggressive nest defenses. Every year, local news outlets all over North America report blackbirds harrassing humans; usually the victims are unsuspecting people just passing by, as I was. In 2020, a Toronto resident video recorded one bird as it dive-bombed multiple pedestrians. The bird now has a TikTok account and social media handle: Dive Bomber Dave. Red-winged blackbirds also dive-bomb much larger bird species that stray too near their nest, such as great blue herons and large raptors.

The red-winged blackbirds’ tenacious nest defense makes sense: the eggs and the hatched nestlings are extremely vulnerable to predators. The list of predators is long. Among them: dogs, coyotes, foxes, snakes, raccoons, squirrels, rats, weasels, and numerous bird species. Probably the main culprit is domestic cats, including house cats, strays, and feral cats, which kill billions of birds worldwide each year. Waterfowl hatchlings have additional worries, including snapping turtles and some species of fish. With so many threats to their young, bird species exhibit a variety of behaviors to protect their nests from danger. In addition to the single-bird aerial assault of the red-winged blackbirds, I have observed several other categories of nest-defense behavior in birds: mobbing, gound assaults, and, my personal favorite, deception.

Mobbing follows the principle that there is strength in numbers. It’s basically an aerial assault by more than one bird on a potential threat, most commonly a predator bird such as a hawk or owl. The objective? To bother the encroaching creature enough that it decides to leave the area. Two days ago I was sitting in my car waiting for a red light to turn green when I saw a red-tailed hawk in flight being mobbed by a group of five much smaller birds (too small for me to identify). The attackers took turns swooping down in front of the hawk’s face and occasionally making contact with the hawk’s back or head. This cooperative defensive behavior is a common sight during the nesting season. Birds as small as chickadees, sparrows, and swallows and as large as ravens and crows engage in mobbing behavior; some observers have seen dozens of birds mobbing a single raptor.

You might be wondering, what chance would the smaller birds have against a large predator? In flight, the smaller birds have a huge advantage of maneuverability—like a Boeing 747 vs. a fighter jet. And a group of birds harassing and attacking the hawk is a much more effective deterrent than one solo assailant. Even if the hawk were able to pick off one of the harassers, the remaining birds would continue the assault. Since it’s to the advantage of many birds to drive a raptor away from a breeding territory, the mobbing group will sometimes include birds from more than one species. A number of different species emit a similar-sounding warning call that alerts them to the presence of a predator. These warning calls both eliminate the predator bird’s advantage of surprise and can serve to recruit potential fellow mobbers. On more than one occasion I have seen the mobbers’ objective met: the irritated intruder flew off, and the triumphant mobbing birds returned to their nesting area.

In another tactic, some birds, especially ground nesters, try to intimidate an intruder with a fierce display. When I observed a group of goslings at close range recently, under the watchful eye of the gander (as I reported in my last post), I knew enough about goose ground assaults to step away as soon as the gander opened his beak to display his serrated bill. He was giving me a clear warning. On numerous occasions I have seen a goose defend its nest, and it’s an impressive and imposing spectacle. If the goose’s loud, vehement, continuous honking doesn’t do the trick, it raises its wings to expand in size and charges straight at the intruder with neck fully stretched out front while raising a verbal ruckus. They also sometimes fly at the intruder to bite and strike with its feet. You truly don’t want to mess with their nests or their goslings.

My favorite bird protective behaviors involve deception, some of which are aural in nature. The burrowing owl, a small, yellow-eyed desert and grassland inhabitant that nests in underground burrows, can accurately mimic the unmistakable warning rattling sound of a rattlesnake, which is intended to ward off some of the owl’s predators. In a visual deception, plovers and some other ground-nesting birds will try to lure a predator away from its nest by scurrying head down and low to the ground to impersonate a rodent.

I first witnessed bird trickery many years ago, when a killdeer fooled me with its acting prowess. I became aware of its presence when I heard its shrill, high-pitched alarm calls, which became increasingly intense and rapid-fire. I spotted the bird as it landed on the ground not far away from me. After landing, it flopped around, its wings at odd and painful-looking angles, all the while calling out as if in distress. Concerned, I slowly approached to see if it was injured. It continued its performance, moving away as I approached, until it decided I was far enough from the nest and calmly flew off. Its wings were sound and intact, but my pride was sorely wounded. The objective of the killdeer’s broken-wing act is to distract a predator away from the nest area or its babies and lure it toward the seemingly disabled adult. Clearly, I can attest its effectiveness.

Robin-sized birds who lay their eggs on a bare patch of ground out in the open, killdeer were named after the sound of their main vocalization, like chickadees were. Killdeer pull out all the stops when it comes to protecting their eggs and young. Speckled in a fine dark gray and white pattern, their smalls eggs are well camouflaged. If an intruder comes too close to the nest, the killdeer issues its warning call and, depending on the threat, will act its broken-wing distraction, take an aggressive posture with outstretched wings, or even charge at the potential predator. Here are first-hand accounts of two of those tactics from Life Histories of North American Birds, by Arthur Cleveland Bent, showing they don’t lack courage:

“Howard Lacey (1911) noticed that a flock of driven goats divided. ‘I walked up to the place expecting to find a rattlesnake, and found instead a killdeer standing over her eggs with upspread wings and scolding vigorously.’ Norman Criddle (1908) writes, ‘If the danger came from a cow or horse, the tactics were changed and the birds with both wings and feathers spread out would run into the animal’s face, and so by startling it drive the intruder away.’”

As I have learned, there’s high drama among birds during the nesting season, with avian actors contributing their fair share of the spectacle.

“Preparation” by Paul Laurence Dunbar

The little bird sits in the nest and sings
A shy, soft song to the morning light;
And it flutters a little and prunes its wings.
The song is halting and poor and brief,
And the fluttering wings scarce stir a leaf;
But the note is a prelude to sweeter things,
And the busy bill and the flutter slight
Are proving the wings for a bolder flight!