Hawks Act as Unwitting Muscle for Hummingbirds

Conservationists often point out that, in nature, everything is connected. Remove a certain species from an ecosystem, and other seemingly unrelated ones might suffer.

Such an invisible thread ties together hummingbirds and hawks. In Arizona, black-chinned hummingbirds situate their nests around those of northern goshawks and Cooper’s hawks. While the diminutive hummingbirds escape the notice of the large raptors, the hummingbirds’ key nest predator, the Mexican jay, does not—and hummingbirds seem to recognize this.

As reported today in Science Advances, hummingbirds that are clever enough to cluster their nests under the protective umbrella of a neighborhood hawk enjoy greater survival of fledging chicks compared to those that don’t.

Ornithologists have long noted a peculiar grouping of hummingbird and hawk nests, but until now, no one had elucidated the relationship behind that phenomenon. To solve the mystery, a team of researchers from Ecuador, the U.S. and Canada carefully observed the comings and goings of hummingbirds, hawks and jays in the Chiricahua Mountains over the course of three nesting seasons.

Their findings established a strong correlation between hummingbird nesting success rates and hawk presence—one that seems deliberately sought out by hummingbirds. Of the 342 humming bird nests the team found, only 20 percent were constructed outside of the range of an active hawk nest.

Additionally, a statistical model the team built showed that more than one-third of the jays’ foraging behavior can be explained by hawk presence. In essence, it seems that jays are actively adjusting their food-finding strategies depending on whether there’s a risk that they might become hawk food.

Jays both avoided hawk nests and, when hawks were around, flew higher above the ground. Hawks prefer dive bomb-type ambushes, so higher flying jays were less likely to get snatched up by the predators. When the researchers mapped the jays’ patterns of avoidance, they found that time and again, the behaviors resulted in a cone-shaped hummingbird safety zone—with the hawk’s nest serving as the vertex.

The presence of a hawk, not just of its nest, also seemed key for hummingbird success. During one season, the researchers observed that predators destroyed four hawk nests. Within two weeks after the hawks had vacated their wrecked aeries, jays had moved into the cone and plundered nearly all of the hummingbird nests in the area. 

Hawks, the authors add, seem to affect hummingbirds without ever interacting with their tiny avian relatives. While none of the four species involved in the study are threatened, the findings neatly illustrate the hidden links that abound in nature, they write. This means that protecting entire ecosystems rather than just one favored species is likely the safest way to ensure that endangered species survive, since removing unrecognized key players could cause the entire system to topple.  

Rachel Nuwer | | READ MORE

Rachel Nuwer is a freelance science writer based in Brooklyn.