Bald eagles face hidden plight

The graceful gliding of a bald eagle is an exceptionally rare sight in most of the lower 48 states - but not in Iowa.

Each winter, Iowa is graced with the presence of approximately five thousand bald eagles from other northern states and Canada. The Iowa Department of Natural Resources reports that up to one-fifth of the bald eagle population in the continental U.S. takes winter refuge in Iowa, particularly around the open waters of locks and dams.

In addition to open-water fishing, bald eagles feed on carcasses of deer and other game that are common in the rural Midwest.

Could the ample fish and game that attract migrating eagles present a hidden threat? The State Hygienic Lab is helping Iowa State University answer that question.

In the mid 1990s, wildlife studies documented the presence of lead poisoning in bald eagles. A 2002 study by Hawk Watch International found that the primary sources of lead in raptors were fishing tackle and spent ammunition. Two years later, Iowa wildlife rehabilitators - including Saving Our Avian Resources (SOAR), the MacBride Raptor Project and ISU's Wildlife Care Clinic - began an ongoing project to determine the level of lead in the blood, liver and bones of eagles admitted to their care.

These researchers came together in January 2012 for a study led by the ISU Department of Natural Resource Ecology and Management to document the fecal and blood lead levels in free-flying and rehabilitation bald eagles. The ISU team chose the Hygienic Laboratory to perform the analysis because of the staff's expertise in using a sophisticated analytical instrument known as an ICP-MS (inductively coupled plasma mass spectrometer). ICP-MS can detect lead (and other metals) at very low concentrations, and with greater speed and precision than other methods.

Samples from more than 100 nest sites are being collected four times over a two-year period. The team expects to gather up to 600 samples of feces, as well as samples of soil, snow, water and vegetation near the nest trees, all of which are being tested for levels of lead. Testing also is under way with blood samples from rehabilitating eagles. The Hygienic Lab's environmental laboratory specialists Steve Bernholtz and Brian Wels teamed to perform the analysis. Bernholtz performs most of the analytical testing on soil, vegetation and feces samples, while Wels conducts the blood sample testing.

"These samples come from a variety of sources," said Billy Reiter-Marolf, ISU Wildlife Ecology graduate student and study leader. Rieter-Marolf works with ISU professors Julie Blanchong, Ph.D., and Stephen Dinsmore, Ph.D.

"The samples from nesting and wintering (migrant) bald eagles are collected from the ground below nest or perch trees. For these birds, we only collect feces, not blood, because we don't want to disturb any wild birds by handling them. We also collect some associated substrate samples at nesting and wintering sites, which are located all over Iowa.

"In addition, raptor rehabilitators are helping us by collecting blood and feces from every bald eagle admitted to their care. With these samples we hope to determine the relationship between blood lead levels and fecal lead levels."

Although blood samples are the most ideal for detecting lead levels, ISU is utilizing fecal samples from the free-flying eagles, because the potential for negative impacts resulting from physically handling birds and climbing nest trees is both undesirable and unnecessary in this type of large-scale field study. The collection of fecal samples is non-invasive and more logistically feasible because samples can be collected on the ground.

The results of environmental testing around the nest of the captive and free-flying eagles will also be compared as part of the study.

Reiter-Marolf and his team will continue sample collection through June 2013. By collecting samples from the same sites in late winter and again in spring, the ISU team hopes to determine if lead levels differ between those samples collected during and shortly after hunting season.

The effect of lead in animals is the same as in humans. It disrupts the nervous, circulatory and reproductive systems, often with devastating outcomes. The ISU study may shed light on the future of the bald eagle in the Hawkeye state.

"If a large portion of the Bald Eagle population is experiencing high levels of lead exposure," said Reiter-Marolf, "concerns would be raised about potential negative effects on survival and reproductive success in the population."