You might think that a nesting bird would want to be as far away from a predator as it could get and, generally speaking, that’s true. However, it could be very strategic to nest near a predator that is two or more steps above you in the food chain (i.e., your predators’ predator). In this way, some birds derive protection from larger, more aggressive species that keep generalist predators at bay. This phenomenon is called a protective nesting association. Here are two of our favorite examples of nest-protecting predators:
Alligators and Wading Birds
In the southeastern United States, researchers found that wading birds such as herons, egrets, ibises, storks, and spoonbills appear to seek out alligator-inhabited waters above which they can nest. The alligators keep away (or eat) nest predators such as opossums and raccoons, and they cannot climb trees to rob nests themselves. However, the alligators certainly claim any chicks that fall out of the nests from time to time, making it likely that they are also benefiting from their avian neighbors.
Hawks and Hummingbirds
Black-chinned Hummingbirds nesting in southeastern Arizona were found to cluster their nests around the nests of Northern Goshawks and Cooper’s Hawks. Both species of hawk prey on birds, but would not normally bother with something as small as a hummingbird. Researchers found that hummers that nested within 300 meters of the hawks were much more likely to successfully raise young than those that nested farther away.
At least 92 such associations have been documented so far. It is unclear whether the recipients of the protection actively seek out these “protectors,” or if they are simply recognizing that an area has fewer nest predators. Either way, it can pay off to have a formidable carnivore for a neighbor…as long as you fly under the radar.
When Melissa Sherwood wrote to NestWatch asking if it was unusual for a Dark-eyed Junco to nest in a birdhouse, we initially thought it was a case of mistaken ID. We told her that juncos don’t nest in cavities, as they are known to be open-cup nesters (although they will nest in crevices or crannies near the ground).
As you may have guessed, she was vindicated. When she submitted the photographic evidence from her Washington home, we couldn’t believe our eyes. Never say never, even when it comes to a very common species.
We searched the NestWatch database to see if anyone else had ever reported this phenomenon, and found an instance of a junco nesting in an open-fronted nest box (the kind designed for Carolina Wrens). We found no other instances in the literature, nor in the historic nest record cards that pre-date our NestWatch project. As far as we know, this is the first instance of Dark-eyed Juncos nesting in an enclosed birdhouse.
Interestingly, our search of the scientific literature revealed two historical mentions of Dark-eyed Juncos nesting in old woodpecker holes, but both sources were more than 100 years old! If cavity nesting is a small and rarely-observed part of their nesting repertoire, that makes Melissa Sherwood the first person in over a century to witness it!
Stay tuned for more details next month about our upcoming photo contest, Home Tweet Home. The contest opens July 1.