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Unanswered Questions
Large raptors like the osprey— active hunters and long-distance migrants—have complicated molt cycles because they can’t afford to be grounded for any significant amount of time.

_Paula Zelanko

Zelanko is a staff scientist at the Academy. Her research focuses on stable isotope geochemistry and analysis.

It’s almost a given in science: the attempt to answer one scientific question sparks other questions to pop up along the way. That was the scenario for Academy of Natural Sciences of Drexel University scientists Paula Zelanko and Nate Rice, who recently launched a study to measure levels of carbon and nitrogen in feathers of the osprey (Pandion haliaetus) from the Academy’s collection to track changes in the environmental health of the Delaware Watershed.

Ospreys are excellent indicators of environmental health because of their place at the peak of the food chain. Feathers hold a unique signature of a bird’s environment and diet—and their molting patterns can tell scientists even more. In the case of the osprey, however, the molting pattern is both highly unique and poorly documented scientifically, so it wasn’t long after Zelanko and Rice began their work that they realized they had to first learn more about this particular bird’s molting pattern before forging ahead.

“This study was originally focused on reconstructing changes in the Delaware Estuary over time by analyzing historic specimens of the osprey,” Zelanko says. “But, all the data analyzed has opened up a new path of research pertaining to Delaware Bay osprey molt patterns, a previously unexplored topic.”

“Most birds molt completely in a single molt season, from the outer feathers to the inner feathers,” says Rice. “But the osprey is molting in a pattern that is unlike any other bird in the New World.”

The basic pattern of molt is known for ospreys, Zelanko says, but it is not well documented where feathers are grown. For instance, researchers don’t know if the feathers arrive at the birds’ breeding grounds or their wintering grounds. This knowledge is important in determining which feathers to sample, however, as Zelanko and Rice didn’t want to sample feathers grown on wintering grounds not located in the Delaware region.

After determining the osprey’s unique use of the Staffelmauser molt, Zelanko and Rice can continue their original objective: to study the nutrient levels in osprey feathers to determine the Delaware Watershed’s health.