Migration Routes Now Mapped
In the birding world, few species generate more excitement than does the “Purple Martin,” a swallow that is arriving now in Texas, with reports of “scouts” logged almost daily online.
Purple Martins, the largest of the swallows in North America, are totally dependent on man-made housing east of the Rockies and faithfully return to the same locations each year, so it’s understandable that human “landlords” anxiously await the return of "their" birds from wintering grounds in South America.
Some of the earliest arrivals to the eastern U.S. occur on the Texas coast and dates/locations are watched by martin enthusiasts nationally on an online database – at www.purplemartin.org -- maintained by the Purple Martin Conservation Association (PMCA), a nonprofit conservation organization.
The earliest arriving martin recorded in Texas this season occurred Jan. 10 in Seguin. Among other early arrivals: Jan. 27 Victoria; and Feb. 3 in San Antonio.
New arrivals represent just a trickle of the population and martins continue to return “home” well into spring. The first wave consists of so-called “adult” martins – those two or more years old, with adult males sporting full dark-purple color. Females are a bit drab, with a gray breast. One-year-old martins – called “subadults” -- arrive 10 to 12 weeks later than the older birds – generally into April. These younger birds sometimes are more easily attracted to new housing locations.
Purple Martins prefer to nest in colonies in gourds hung from large racks and in multi-compartment birdhouses. The birds nest throughout central and eastern Texas with the greatest populations east and a gradual absence in West Texas.
Recently the PMCA has helped launch high-tech research into the winter migration whereabouts. It was known that Purple Martins winter in South America, but a few dozen individual birds have now been fitted with tiny “geolocators,” a type of light-sensing device attached the birds’ backs to precisely track their movements.
When individuals return in spring, they are briefly captured, their geolocators removed and the data downloaded to draw a map of their movements. It’s now learned that most winter in Central Brazil, and not southern Brazil as previously believed.
The route back also had been unclear, but tracking birds tagged originally in Corpus Christ, it’s now been found that some Texas martins follow the coastline of Mexico northward, while others make a gulf crossing – as previously assumed -- leaping northward off the coast of the Yucatan. Also significant, Purple Martins nesting further to the north and west, up into MN, the Dakotas, and Alberta, Canada, all pass through Texas on their trip home.
For reasons that are unclear, new arrivals sometimes show up on warm fronts just as the wind direction is turning to the north – the “fall out” phenomenon as birders call it where many exhausted bird species “fall out” along the coast.
Because martins feed on the wing – taking insects from the air –arrivals during cool periods sometimes face starvation. However, hobbyists have learned to supplemental feed the martins from feeder trays, inside their compartments and sometimes by actually flinging bits of scrambled egg or thawed crickets into the air..
A PDF information sheet about supplemental feeding -- the techniques are still new to many hobbyists – can be found at the PMCA’s website at www.purplemartin.org.
The PMCA recently analyzed long-term data from the North American Breeding Bird Survey (BBS) and found that – thanks to devoted men and women who erect and maintain housing – purple martin populations overall are holding steady in North America – with exceptions in some states -- and appear to be increasing in Texas.
Many parks and public areas in Texas host colonies of the birds, including a newly established colony at the South Texas Botanical Gardens in Corpus Christi. In San Antonio, students maintain a thriving colony at John Jay High School. In Grand Prairie, members of the Purple Martin Landlords of North Texas - http://www.purplemartinlandlordsofnorthtexas.com -- conduct ongoing educational events.
At the height of summer in July, Texas martins gather in huge pre-migratory roosts at night in preparation for fall migration. Some contain tens of thousands of birds and one of the largest in Texas occurs at the Highland Mall in Austin, with local martin hobbyists gathering at sunset to watch the martins arrive.
Despite the relative abundance of Purple Martins in Texas, many people try for years to attract them without success, or their colonies disappear. Hobbyists may be unaware that problems such as competition from invasive non-native birds -- European starlings and House Sparrows -- or predation caused abandonment.
While generations of Americans have hosted Purple Martins – the custom adopted from Native Americans who hung out nesting gourds – specific techniques to help a colony thrive emerged in the past decade, based on research conducted by the PMCA and landlords in the field.
Among innovations are deeper compartments to protect nestlings from rain and aerial predators such as owls, specially-shaped entrance holes designed to admit martins while restricting starlings – and unique pole guards to thwart climbing predators: rat snakes and raccoons.
Because Purple Martins are birds of the open sky -- catching insects on the fly -- the PMCA's number one tip: place housing in the most open space available, but where the colony can be enjoyed and monitored.
More information about Purple Martins can be obtained from the Purple Martin Conservation Association – which is focused on aiding martins and landlords -- including an information and supplies booklet, with advice on attracting and managing a colony, and data sheets to participate in a “citizen science” program called Project Martinwatch, an international effort in which participants monitor nests and mail information to the PMCA at season’s end.