Tuesday, May 26, 2009

Banding a Raptor

Cooper's Hawk (male) - banded May 18, 2009

This season's bird banding sessions have been productive and entertaining for a great number of elementary students. Preparing for this program requires 2 hours of netting/trapping birds prior to the student's arrival. It's the best way to ensure that our visitors will see at least a few different species of birds upon their arrival.

During this prep time we often experience some of the most memorable encounters with species not usually encountered at our banding station. Three years ago, we netted a Mourning Warbler just moments before a nursery school group was about to arrive. Two years ago, Steve netted a Great-crested Flycatcher, and a year ago we had a near-miss with a Northern Flicker who managed to weasel its way out of the net before we could get a hold of it. This year's most memorable behind-the-scenes moment occurred last week with the capture of an unsuspecting Cooper's Hawk.

A few minutes after 8am, Steve and I were approaching the banding station to remove a few birds from the mist net. We noticed a Mourning Dove hanging lazily in the net. They usually free themselves from the net since they're a bit larger and bulkier than the small species. That morning was no different, but the dove's quick escape from the net was initiated by a suprise attack from a Cooper's Hawk. The hawk divebombed from the opposite side of the net, so the dove escaped. The hawk did not.

Cooper's Hawks attack unsuspecting prey with blinding speed and a fierce set of talons directed forward the bird's body. The talons simultaneouly secure and subdue the prey. When this hawk attempted to grab the dove, his talons and legs became quickly tangled in the net. Since we were on the scene when this all happened, we were able to safely immobilize the hawk and remove it from the net. This was done with our and the hawk's well-being in mind. (Take a look at the talons pictured below)

Adult male Cooper's Hawk: note horizontal barring on chest and red-colored iris of eye

Talons: Razor-sharp and capable of subduing prey and piercing Steve's glove and flesh

Sexing (if possible) and ageing the bird are two critical pieces of information needed before banding a bird. Most species of song birds are sexed reliably in the spring due to color variation or presence of a brood patch (bare skin on the female's belly) or cloacal protuberance (fairly obvious male feature). Hawks are sexed based on size since females are larger than males. Simple measurements were done to determine this Cooper's to be a male. Its plummage pattern and iris color identified it as an adult.

Cooper's Hawks and Sharp-shinned Hawks are common in our area throughout the spring, summer and fall. They hunt small prey, usually small mammals and birds, in the forest canopy and understory. They will make an appearance at a bird feeder from time to time as well, but they're not looking to enjoy seeds...just seed eaters. Due to their smaller size and habitat preference, they are encountered far less often than the larger Red-tailed Hawks, also common in our area.

The picture below shows some of the field marks used to identify this Cooper's Hawk from the similar-looking Sharp-shinned Hawk. Note the large head of this Cooper's compared to the shrunken-headed appearance typical of a Sharpie. Also the tail feathers of the Cooper's appear much more rounded on this bird in contrast to the flattened ends of the Sharpie's tail feathers. Relative size is also an important cue as well: Cooper's are crow-sized birds and Sharpies are Blue Jay-sized birds.

-Adam Zorn, Naturalist

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