Hummingbirds and Hawks
By Andrea Peck
Last week I talked about birds and their ability to alter their reproductive habits depending upon their assessment of predator presence. Though the researchers who conducted that study did not conclusively decipher ‘the why' of bird behavior, they did successfully establish that birds are capable of monitoring their environment and responding to it, particularly when it comes to reproduction.
Another, more recent study has found that one bird, the hummingbird, is capable of selecting nesting sites that provide them with protection from one of their main predators. The study, done at the Southwest Research Station in Arizona, focused on the behavior of black-chinned hummingbirds (Archilochus alexandri), Mexican blue jays (Amphelocoma wollweberi) and the northern goshawk (Accipiter gentilis) and the Cooper's hawk (Accipiter cooperii).
In this area of southeastern Arizona, both the northern goshawk and Cooper's hawk are prevalent top or apex predators. Generally, the hawks build their nests near the tops of the tree canopy. While the fierce hawk with its predatory mystique may seem intriguing, if you have the darting eye of a scientist, you might observe some little nests dappled beneath the hawk's rugged twig-strewn lodging. Then you may wonder what those are doing there. And why.
Those artistic nests made from spider web and plant down belong to the hummingbird. Smart hummingbird parents, the researchers found, select a locale that is just near enough to the predatory hawk in order to avoid their own personal threat --the Mexican blue jay. The jay has a known predilection for the eggs of the hummingbird.
You may wonder how a tiny hummingbird stands a chance, but in this particular area, the hawk shows little interest in the paltry, snack-sized hummingbird or its eggs. Both types of hawks prefer a meal over an appetizer and a medium-sized bird, such as the jay, fits that bill. The northern goshawk is a powerful raptor that hunts crows, hares and squirrels. The Cooper's hawk grabs its prey with its feet, squeezing the animal until it is dead. They have been known to drown their prey by submerging it in water.
When in the presence of hawks, the jay alters its flying pattern to keep a better eye on the hawk. The jay, on its own flies at all levels, but when a hawk is near, it flies at or above that of the hawk. Hawks search for food in a dropping motion—if they are located at the top of a tree, they swoop down at an angle in pursuit. If you picture the space between the top of the tree and the angle of “hawk coverage” you will have an idea of what researches describe as the “cone of protection.”
The researchers were able to determine that 80% of hummingbirds elected to live in association with hawks. The other 20%, left unprotected, had significantly less survival rates. Furthermore, it was clear that the jay altered its foraging patterns when in the presence of hawks.
It is likely that the powerful hawk has no idea that it is providing such a service. On the other hand, the world of animals is a mysterious one which is often underestimated. Perhaps that is where the real study lies.
To see the actual study view this link: