On September 29, Rhonda Little-Aifa posted photographs of an unfamiliar hawk on the Maine Birds Facebook page. The bird was at the Millinocket Airport on Medway Road, first seen a few days earlier.
Doug Hitchcox, the Naturalist at the Maine Audubon Society, recognized the bird as a Swainson’s Hawk. Swainson’s Hawks nest on cliffs near grasslands in western North America and spend the winter in South America, as far south as Argentina.
Clearly, this was a bird out of place. The Maine Birds Checklist Committee recognizes only two prior records for the state, one seen on May 3, 2009 in Pownal and on seen on September 23, 2013 in Harpswell. Eight other reports of this species, dating from 1883 to 2005, have not yet been reviewed by the Checklist Committee.
A major migration of birders to Millinocket began on September 30. Dozens of birders got to see this cooperative bird, particularly over the weekend. The hawk was last soon on the morning of October 4. You can see pictures at: http://ebird.org/ebird/view/checklist/S31826769
Swainson’s Hawk belongs to the genus Buteo, the genus that also includes the familiar Red-tailed Hawk and Broad-winged Hawk. Swainson’s has proportionally longer wings and a smaller bill than the similarly-sized Red-tailed Hawk.
Swainson’s Hawk has colloquial names of locust hawk and grasshopper hawk. The hawks feed often on the ground, chasing grasshoppers, a favored food. The Millinocket Bird spent most of its time perched on the fence surrounding the airport or walking/running on the ground, chasing down grasshoppers. Louis Bevier made a video of the hawk capturing a grasshopper: You can watch the video at: https://vimeo.com/185072912
Swainson’s Hawks will also catch dragonflies and other large insects on the wing.
Normally, Swainson’s Hawks migrate south from their western breeding grounds, through Central America and then spread out in South America. Like most Buteo hawks, Swainson’s Hawks are averse to migrating over water.
Swainson’s Hawks are one of the most abundant species migrating through the Isthmus of Panama. Hawk watchers in Panama City counted 900,000 soaring migrants (mostly Swainson’s Hawks and Turkey Vultures) passing overhead on a single day in November of 2013. That record was eclipsed on November 2, 2014 when 2.1 million birds passed over. What a spectacle that must have been!
This hawk joins a long list of vagrants to Maine from western North America. These birds include White-winged Dove, Western Flycatcher, Calliope Hummingbird, Hermit Warbler, Brewer’s Sparrow, Black-throated Sparrow and Western Meadowlark.
I think it is significant the the Millinocket Swainson’s Hawk was a young bird, born in the summer of this year. Many birds that appear in unexpected places during migrations are naïve, inexperienced birds. Young birds are much more likely to make navigational errors than more experienced birds.
Navigation during migration involves two abilities. Most migrants are capable of vector navigation, maintaining a particular compass direction for a specified length of time or distance. True navigation requires that a bird knows exactly where it is, even if it is displaced by a storm or wind.
Experiments demonstrate differences between the navigational abilites of juvenile and adult birds. Imagine Yellow-rumped Warlers banded on their breeding grounds in Maine that normally would migrate south to North Caroina for the winter. Vector navigation in a south-southwest trajectory will get those birds to their wintering grounds.
Some ornithologists have experimentally captured such birds and displaced them eastward or westward. Let’s fly some warblers from Maine to Minnesota and release them there in the fall. Adult birds have true navigation; they realize where their displaced position is and will migrate in a southeasterly direction to get to North Carolina. The young warblers are poor at true navigation. Most will use their vector navigation skills and head south toward Texas. Vagrant birds therefore tend to be young birds that are much more likely to get lost.