Reprinted from: Purple Martin Update 10(1): 6-7
James R. Hill, III
Purple Martin Conservation Association
Previously, the Purple Martin Conservation Association has published relative abundance maps for the Purple Martin, population trend maps, a south-of-the-border band recovery map, breeding range maps, migration-timing maps, and a winter range map. Here, for the first time, we are publishing a map that shows the northward migration routes of the Purple Martin as it returns to its North American breeding grounds. The map on the facing page also includes the martins breeding range, winter range, and its arrival timing on the breeding grounds. This map is also featured on the PMCAs new educational poster (see page 26).
The purple background on this map shows the winter (non-breeding) range of the Purple Martin (Progne subis) in South America and the breeding range in North America. The Purple Martin breeds only in the United States, Canada, and scattered parts of Mexico. It winters only in South America. There are no reliable reports of the Purple Martin overwintering in Florida, Texas, Mexico, Cuba, or Central America, and likewise, no reports of it breeding in South America. You will not find the Purple Martin in Europe, Asia, or Africa, either. It is strictly a New World species. Most scientists now believe the Purple Martin is actually a South American swallow that evolved its migratory habit to North America so that it could take advantage of the longer summer days unique to the northern latitudes. Longer days give the Purple Martin more hours of daylight each day to gather insects for its growing young.
At the end of the breeding season, the Purple Martin migrates back to its tropical home in South America where it molts an entirely new plumage of feathers. The Purple Martin spends its non-breeding season in eleven different South American countries: Colombia, Venezuela, Ecuador, Peru, Bolivia, Paraguay, Argentina, Brazil, British Guyana, Suriname, and French Guiana.
The red arrows on this map show what are believed to be the main northward pathways that the Purple Martin uses when migrating between its South American wintering grounds and its North American breeding grounds. A few leave the north coast of Venezuela and strike out across the Caribbean, island-hopping their way north into Florida. Evidence suggests that his is the least used northbound route. The vast majority of Purple Martins leave South America by travelling up the isthmus of Panama; the two western subspecies (Progne subis hesperia and Progne subis arboricola) apparently take the Pacific coastal route up the western edge of Central America and Mexico, while the eastern subspecies (Progne subis subis) takes the Caribbean/Gulf of Mexico coastal routes. Observers in Central America rarely report seeing migratory martins away from the coasts.
Once P. s. subis reaches the Yucatan Peninsula of Mexico, it splits up and goes in three different directions. Some stay over land, hugging the coast, and go westward around the Gulf of Mexico into Texas. The rest strike out over the open waters of the Gulf of Mexico, aiming either for the west coast of Florida (500 miles away), or the Mississippi Delta of Louisiana (600 miles away). Its not uncommon for Purple Martins to land on ships, oil drilling platforms, or even floating debris to rest if they run into bad weather while making this potentially perilous crossing of the Gulf.
The purple lines on this map are isochronal arrival waves that mark the average first-arrival dates of adult martins at long-established breeding sites (landlords with younger, or smaller, colony sites typically have martins that begin arriving slightly later than the dates shown here). Because of southern Floridas subtropical climate, martins always appear first in North America there, often during the first or second week of January. They usually dont begin arriving in southern Louisiana until the last week of January, or the first week of February. The same goes for those birds taking the much longer land route around the Gulf to Texas. Typical first-arrival dates in southern Texas arent until the third or 4th week in January, or even early February. The birds making the 500 to 600 mile Gulf crossing to Florida and Louisiana do it nonstop in about 25 to 30 hours, whereas the birds going around the Gulf (which have about 1200 miles to travel to reach the United States) do it at a leisurely pace and apparently take about two weeks.
Interestingly, if you were to freeze the calendar at the very moment P. s. subis was first observed back in Texas, Louisiana, and Florida, it would be absent from all the intervening areas, demonstrating this three entry port phenomenon. The three isochronal wave crests along the Gulf of Mexico (shown on the map), further corroborate that the martin arrives in eastern North America via three main corridors (i.e., Texas, Louisiana, and Florida).
The arrival of the martin at each latitude is a long, drawn out phenomenon. It lasts about 10 weeks in the northern part of its breeding range, 16 weeks in the central part, and 22 weeks in the southern part. Yearling martins (i.e., subadults), the age group that most typically colonizes new breeding sites, dont begin arriving until about 4-6 weeks after the earliest adults do in the north (8-10 weeks after the adults in the south). The time window for attracting martins is quite wide. We continue to learn more about the arrival schedule of Purple Martins in North America via the PMCAs Scout-arrival Study. We encourage all of our members to send us their adult and subadult arrival dates each year.
Copyright 2001 by Purple Martin Conservation Association. All Rights Reserved.
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