I recently became aware of an odd housing situation in Barnstable. There’s a neighborhood where, for mysterious reasons, sworn enemies are living shoulder to shoulder in an uneasy peace. In this housing-strapped market, old feuds were set aside for the sake of convenience and safety from common enemies. I am of course talking about birds here. This is the story of the hawk and the hummingbirds.
Local wildlife photographer Diane Palomba has a keen eye for wildlife, and a knack for getting National Geographic quality videos of things like otters, minks, and owls of the sort that make other photographers jealous. It was this keen eye that found not one but four tiny hummingbird nests in a small area of Mass Audubon’s Long Pasture sanctuary in Barnstable. Astoundingly, property manager and birder Chris Walz found two more. That made at least six nests in an area of maybe two acres, and oddly, all were fairly close to a well-known Cooper’s Hawk nest. Chris reminded me about an amazing study from out west that likely explained this unusual density of hummingbird nests, and the seemingly odd choice of neighbors.
In the early 2000’s, an ornithologist named Harold Greeney noticed that Black-chinned Hummingbirds, the closest cousin to our Ruby-throated Hummingbirds, were nesting in clusters in Arizona – he would find no nests over long stretches, then suddenly several in a small area. Eventually he figured out why, and published the results. It turned out at the center of each cluster of nests was a Cooper’s Hawk nest. But why? Cooper’s Hawks are inveterate bird eaters – small birds is most of their diet, and a nesting pair of Cooper’s Hawks with mouths to feed would presumably be pretty hungry for small birds.
But he tracked nesting success of hummingbirds that did or did not nest near hawk nests and found a stunning advantage to nesting near the hawks – 46% nest success versus less than 10% if they weren’t near a hawk nest. In a follow up paper he showed that it was by keeping jays away that the hawks benefitted the hummingbirds – jays were the most common nest predator, as they are around here, and the jays, juicier prey for the hawks, avoided the hawk neighborhood, with the protection from the jays extending about 300 meters from the hawk nest. The hawks don’t seem to get anything out of this, so for you animal behavior terminology buffs out there, this type of symbiosis qualifies as a commensalism.
Other species exhibit this “strange bedfellows” nesting strategy. Some species of trogon, colorful tropical birds, nest in active wasp nests, which, somewhat absurdly, they use as both a snack station as well as protection from predators. And some Arctic geese have higher nest success near Snowy Owl nests, apparently because the owls will chase off Arctic foxes, the main threat to the geese.
If I can get back to our local hawk and hummingbird commune at Long Pasture, there’s one more odd fact about the nests: all are in different tree species. European larch, maple, pine, cherry, oak, and finally a holly. So if you want to find a nest, or six, in your own neighborhood, the tree species obviously doesn’t matter, but they do like to nest on a downwardly angled branch with an open area below and leaves above. If you’re lucky enough to find one, you’ll see the nest is a tiny work of art, a thimble-sized sculpture rendered in spiderwebs and lichen, a masterpiece of camouflage resembling nothing but a bump on a branch. But if you really want to find some, step one, apparently, is to find the Cooper’s Hawk nest.
