ERIE, Pa. — The bait bird didn’t work as well as Beth Potter had hoped.
To broaden her study of the microflora that coats certain bird eggs, Potter, an associate professor of microbiology at Penn State Erie, The Behrend College, needed access to eggs. To get them, she needed more birds.
She started with house wrens. They’re common, and they will nest in just about anything, including cans, boots and boxes. Potter repurposed several nest boxes that had been left on the former St. John Kanty Preparatory School property, which the college purchased in 2010. She checked them as often as she could.
“I was always an ‘in the lab’ type of person,” she said, “so that was a nice change. It was interesting, being out there.”
The property was otherwise unoccupied, except for the occasional angler walking to the pond. As the grass grew higher, Potter felt the nesting boxes were too remote, particularly if she took along students, who do much of her sampling work.
She switched to Purple Martins — fast, acrobatic fliers that congregate in large colonies, often near open water. She partnered with the Purple Martin Conservation Association (PMCA), an Erie non-profit that maintains several nesting sites at Presque Isle State Park. Martins are unique in their nesting preferences: In the Eastern United States, they almost entirely rely on man-made structures.
Potter and her students swabbed eggs in the PMCA colony, analyzing the bacteria on the shells. They found Pseudomonas, which is common in water and plant seeds, but very little enteric bacteria, which is passed through the intestinal tract. That suggests the eggs are coated with bacteria after they are laid, or that the microflora kills off or otherwise reduces the enteric bacteria, which could cause disease.
“The big question,” Potter said, “is, why? If this is a microflora that is being continuously maintained, what purpose does it serve?”
The coating might protect the shells from the more harmful intestinal bacteria. It also could make the shells more porous, easing the process when the birds hatch.
Another question is how it gets there.
“We don’t yet know if it’s on there at birth, or if it’s added later, through preening,” Potter said.
Most birds have a uropygial gland just above their tail; the oil that secretes from there helps to keep their feathers flexible and waterproof. In some species, including Purple Martins, the composition of that gland oil changes when the mother is incubating her eggs. It’s possible, Potter said, that the oils are transferred to the egg during preening.
In 2015, Potter tried to establish her own colony. Using materials donated by John Tautin, an alumnus and former executive director of PMCA, she put 12 gourd-shaped Purple Martin houses on a tall pole in the field behind the Otto Behrend Science building, a short walk from her office. She set a portable CD player at the base and played Purple Martin dawn calls, which are meant to draw other birds to the colony.
A single family of Purple Martins nested on campus that year. They had four hatchlings.
Potter set the houses out again in 2016. She replaced the CD player with a Bird-x Songbird Magnet, which played four hours of Purple Martin chatter every morning. She added the bait bird — a plastic Purple Martin fixed to the top of the pole.
Again, one family nested. Potter suspects it was the same pair that nested there in 2015. They chose the same box.
Soon, there were six eggs.
Potter hopes to test another generation of eggs this summer. A better understanding of the bacteria on the shells eventually could help conservation efforts, she said.
It can take years for a Purple Martin colony to form, however. The birds favor established sites and often return to the place where they last nested. Scout birds arrive first, usually reaching Erie in early April. The Purple Martin Conservation Association tracks them on its website.
“Purple Martins are a finicky bird,” Potter said. “You have to work to get them to come to you. We’re getting there.”