Purple martins

 Quick facts:

• Largest swallow in the Americas 
• Progne subis, originally named Hirundo subis by Linnaeus 
• Sexually dimorphic. Adult males blackish with iridescent blue or purple sheen. Females brown with some iridescence on back, soft grey or tan below.
• Long-distance migrant. Breeds on localised basis throughout eastern North America, with disjunct populations on the Pacific Coast, in the American Southwest,  and in Mexico. Winters in South America, primarily in the Amazon Basin.
• Cavity nester. Often breeds in colonies. Eastern populations highly dependent on artificial nesting structures. (See below.)

Humans have been hosting purple martin colonies for at least three or four hundred years; the Cherokee Indians apparently hung hollowed-out gourds to attract the birds before European contact, and the practice was also observed among the Choctaw and Chickasaw peoples in the early nineteenth century. (Purple martins are prodigious insectivores, and their presence offered some protection to nearby crops, though obviously there were aesthetic benefits as well.) European-Americans followed suit, introducing framed martin houses that more closely approximated their own homes. Apartment-style martin houses in particular can support especially dense nesting colonies.

The importation of English sparrows and especially European starlings by those same European-Americans, though, effectively neutralised or reversed the benefits of providing such housing, as these species are also cavity nesters and are more aggressive than the native martins. By the latter half of the twentieth century, widespread population declines had been noted, with purple martins becoming decidedly rare in parts of their range. It is not enough to provide nesting locations—purple martin "landlords" must actively manage their colonies, ruthlessly removing and destroying English sparrows and European starling nests (and killing the invasive birds themselves when possible) to give the more docile martins a chance.

We photographed these purple martin colonies at two widely separated locations: Alligator River National Wildlife Refuge in eastern North Carolina and the Land Between the Lakes National Recreation Area in western Kentucky. Public-lands colonies such as these look to be increasingly important for purple martin survival, as demography seems to be working against private colonies: "One study found that nearly 90% of landlords were 50 years of age or older, and that younger generations were not exhibiting the same enthusiasm [or did not] possess the resources to provide martin housing for the species." Even public-lands colonies are often dependent on volunteers (again, often older individuals) for their monitoring and maintenance. Unless such trends are reversed and the birds can gain a broader base of support, the purple martin's current IUCN status of "least concern" may be unwarranted. 

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ARNWR, NC

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LBL, KY