Wednesday, September 2, 2015

Two ways not to fly over the Gulf of Mexico

Our colleague and collaborator, Dr. Jennifer Coulson of Louisiana’s Orleans Audubon Society, tagged two adult Swallow-tailed Kites at the close of the 2015 nesting season. The following account describes the start of their southbound migration. 

During either their spring or fall migrations, Swallow-tailed Kites from the western subpopulation (Alabama, Mississippi, and Louisiana) may fly south directly across the Gulf of Mexico, or they may head west and travel entirely overland, following the Gulf coastline through Louisiana, Texas, and Mexico. This year, both tagged birds from the western subpopulation circumnavigated the Gulf, but one surprised us by taking an easterly track. 

Jennifer and Tom Coulson prepare to
release Strong River. © Jennifer Coulson
Strong River, newly-tagged near his nest in central Mississippi, left his summer range quite early for a bird west of the Florida Panhandle. After departing his breeding territory, he headed southwest to a known gathering area on the Sabine River, along the Louisiana–Texas border. He spent some time there, probably foraging daily with other kites and fattening up on insects, before moving southward through Texas. By 1 August, he had crossed the Mexican border, then spent the next eight days continuing south along the coastal plain within 20 miles of the western shore of the Gulf of Mexico. Strong River slowed down once he reached Guatemala and Belize. Perhaps he began encountering large numbers of Swallow-tailed Kites that had migrated through Florida and across the Gulf of Mexico, making landfall just to the north and resting after their 400+ mile over-water flight. As we know from years of satellite tracking and Gina Kent’s Masters’ research, this region in southeastern Mexico and northeastern Central American is the most vitally important stop-over area along the U.S. population’s 5,000 mile southbound migration route.

Strong River circumnavigates the Gulf to the west, typical for a bird of the western subpopulation. 

Lacombe. © Jennifer Coulson
Adult male Swallow-tailed Kite Lacombe, tagged by Jennifer in southeastern Louisiana, surprised us all by taking an eastern route through the Florida Panhandle and then turning south through the Florida peninsula. He spent one night in a known roost in Citrus County, Florida, then the next near another roost in the Corkscrew Swamp in Collier County before sailing off the southern shore of remote Cape Sable (the southern tip of the Everglades and Florida) late in the afternoon of 10 August. Lacombe passed over the Florida Keys that night and headed west past the Dry Tortugas to begin his 400-mile crossing of the Yucatan Channel. We have learned that the trans-Gulf flights for most tagged kites begin in the afternoon, perhaps giving the birds the advantage of cooler temperatures and less water loss while flying through the night. Lacombe reached the northern tip of the Yucatan Peninsula 42 hours later and settled in not far south, probably resting and regaining weight by feeding over the expansive tropical forest and scattered Mayan temples west of Tulum, Quintana Roo, Mexico. 

Lacombe, although tagged in Louisiana, takes a route typical for birds of the eastern sub-population.

Thanks to Jennifer Coulson for raising the necessary funds and safely capturing and tagging these birds just before they left the country. We are grateful for her contributions to the Swallow-tailed Kite tracking study over the years.