Isotopes and Telemetry Reveal Golden Eagle Migratory Patterns

By Joshua Rapp Learn

Eastern golden eagles face threats such as habitat loss and wind energy development. A recent study tracked golden eagle populations to find out how different populations connected.

Image credit: D. Brandes

New research on hydrogen isotopes on golden eagles shows that at least some birds of a feather may fly together.

While researchers have long known more or less where eastern golden eagles (Aquila chrysaetos) come from and where they end up during their migrations, they haven’t known about many of the specifics including whether some subpopulations always group together, and how much connectivity there is between the birds.

“Establishing these patterns of connectivity is really important to conservation,” said Todd Katzner, a research wildlife biologist at the U.S. Geological Survey’s Forest and Rangeland Ecosystem Science Center and a coauthor of a new study published this week in The Condor: Ornithological Applications.

To get a better idea of population dynamics, the research team took hydrogen isotopes from feathers they gathered in winter and summer areas. The water that eagles ingest in different areas contains consistent isotope patterns that can indicate where the birds spent their time. The researchers combined this with telemetry for control, though the gathering of feathers is much cheaper and gives a broader picture of the population makeup.

Based on the data, researchers determined that eagles that spend their winters in Pennsylvania generally spend summers in the mid-latitudes of Quebec, for example. The eagles in general also exhibit what Katzner calls an intermediate level of connectivity between eagle populations — something he said is good due to the fact that it may allow the birds to be more resilient in the face of habitat destruction. For example, if something happens to a population of birds in the summer grounds due to resource development in their area, it won’t necessarily affect an entire wintering population down south, and vice versa.

He also said that connecting different birds’ summering and wintering grounds will allow conservationists to better understand factors affecting different populations. “It underpins a huge amount of conservation action.”

Joshua LearnJoshua Rapp Learn is a science writer at The Wildlife Society.

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