Like the cliff swallows that return to Mission San Juan Capistrano in California every spring, the swallows known as purple martins have been returning to Tulsa, Oklahoma, every summer for decades. That may change when word gets out across the telephone lines that hundreds of purple martins mysteriously fell to the ground dead this week. The swallows are dead and Oklahoma purple martin fans are depressed, but mosquitoes in Tulsa are happy. What happened?
Tulsa is a main stop on the annual purple martin (Progne subis) migration from as far north as Canada to as far south as Ecuador. The layover in Oklahoma generally lasts from July to September for the largest North American swallow, whose population has been dropping due to competition for nesting spaces with European starlings and house sparrows. That’s why Oklahomans cherish their appearance each summer in downtown Tulsa, where up to 200,000 of the birds used to roost around the DoubleTree Hotel Downtown.
This year, the birds mysteriously avoided the Doubletree and instead all moved to the Sun Building. Tenants there were happy to see the purple martins ... until July 19th when they found hundreds of the birds dead or dying on the ground. Local purple martin expert Dick Sherry was called in and believes a heavy rain that morning soaked the birds to the point they were too heavy to roost on branches or fly and fell to their deaths. Bird experts from local colleges are examining some of the carcasses to see if there might be another cause, like poisoning.
The real mystery is why the birds suddenly changed roosts. Urbanization removes forest nests, the mess made by droppings causes building managers to remove city nests, and starlings and sparrows take over purple martin nesting houses unless owners chase them away. The swallows stopped coming back to Capistrano for many years after workers repaired cracks in the old mission buildings and removed the mud nests built in them. Could this be why the Tulsa martins moved away from their former safe roosts … a move that sent many to their deaths?
The mystery may not be solved until next year when the purple martins hopefully come back to Tulsa.