Researchers using a novel combination of weather-radar data, flight-call recordings, and wind measurements have provided new insights into the magnitude and direction of the puzzling movements known as morning flights.
Night-migrating birds make the flights after dawn, moving above tree height either singly or in loose groups and usually in the direction in which they migrated the night before, but not always; sometimes morning flight is in a direction opposite their intended goal.
A team including Paul Kerlinger, David Sibley, and Richard Crossley documented morning flight among more than 60 species of autumn migrants at Cape May, New Jersey, in 1988 and 1989. The researchers concluded that the flight consisted of birds returning to land after being blown out to sea the previous night, birds compensating for lateral drift incurred during migration, and birds seeking habitat where they could rest and find food.
In the latest study, conducted in fall 2010, Benjamin M. Van Doren from Cornell University and investigators from the University of Massachusetts at Amherst and the Cornell Lab of Ornithology compared morning flights at seven inland and coastal locations in New York and Pennsylvania.
Read the abstract
Benjamin M. Van Doren, Daniel Sheldon, Jeffrey Geevarghese, Wesley M. Hochachka, and Andrew Farnsworth. 2015. Autumn morning flights of migrant songbirds in the northeastern United States are linked to nocturnal migration and winds aloft. The Auk: Ornithological Advances 132 (1): 105–118. Abstract.
Morning flights were larger in coastal areas than inland, despite the fact that nocturnal migratory movements were generally larger farther inland. Moreover, flights were larger on mornings following nights in which breezes were more likely to push birds off course. The results, write the researchers, suggest that “the drive to compensate for wind drift contributes to observed morning flights in concert with the search for appropriate stopover habitat.”
Just as interesting, morning-flight directions differed from site to site. Migrants near Ithaca moved south-southeast, for example, while birds in Manhattan flew west and birds in Rye moved north-northwest, leading the researchers to conclude that local conditions, such as topography and the distribution of suitable habitat, are also important considerations when interpreting the direction of morning flight.
Van Doren and his colleagues published their study in The Auk: Ornithological Advances, the journal of the American Ornithologists’ Union.
A version of this article appeared in the February 2015 issue of BirdWatching. So go ahead and subscribe already!