Bald Eagles and Airplanes

[Donna]

   
   
Homen Airfield is located on the shores of the Mississippi River in downtown St. Paul.

Holmen Field is located near downtown St. Paul and on the shore of the Mississippi River, also prime eagle habitat. The close proximity of eagles and airplanes pose a threat to both people and the birds.

In late May 2009, during the early morning hours, a Learjet 45 rolling down the runway at the St. Paul Downtown Airport struck an immature bald eagle, partially ingesting the bird into one of its engines. The aircraft aborted takeoff and no one aboard the plane was injured, but the collision killed the eagle. The young eagle had a band around its leg indicating it had fledged from a nest south of nearby Pig’s Eye Island the previous year.

This collision, or “birdstrike,� highlights the safety issue eagles and other birds present to aircraft. And at the St. Paul Downtown Airport (also known as Holman Field), an increasing number of bald eagles have taken to congregating by this airport that resides next to a large bend in the Mississippi River and within the Mississippi National River and Recreation Area. Why these eagles are attracted to the area and is something that requires further investigation.

The Threats
Having an average size range of nine to 11 pounds, bald eagles are exceptional threats to aircraft because their large size is more than twice the weight at which most airframe components are tested for airworthiness. Most strikes occur less than 500 feet above ground when planes are landing or taking off. This is the same altitude raptors hunt for prey, when soaring, or flying between perches. The change in technology to the faster jet aircraft and longer runways provides less time for birds to react and move away from oncoming planes.

Direct strikes, however, are not the only problem as eagles can have indirect effects too, such as interfering with communications by perching on antennae or droppings and nesting material short-circuiting electrical systems on the ground. All of these situations can lead to damage that cost a considerable amount to repair.

Finding Solutions
Since 2000, the St. Paul Downtown Airport has been working with Wildlife Services, a program of the U.S. Department of Agriculture Animal and Plant Health Inspection Service, to conduct a wildlife hazard assessment of the bald eagles. The assessment indicates three to five active nesting sites within one mile of the airport. Hazing with firecracker-like devices known as pyrotechnics are the primary method for hazing bald eagles from critical airspace and the airport, but it appears that this method only offers limited relief because the birds become increasingly tolerant of the noisemakers and return a short time later.

Surveys conducted by Wildlife Services indicate that juvenile eagles (less than 4-years-old) are the most frequently hazed, and that the eagles are present at the airport from February to October with March showing the highest number of visits.

In 2007, recognizing that current methods are not working satisfactorily, Wildlife Services in Minnesota received the first permit ever issued to capture and relocate immature bald eagles. In this pilot study, researchers will capture up to five immature bald eagles known to pose a persistent threat at or within one-half mile of the airport. After capture, the eagle will be checked over by veterinary staff at the University of Minnesota Raptor Center, banded and fitted with a small backpack carrying a satellite transmitter capable of tracking the eagles for at least 18 months. The goal will be to track the movements of the relocated eagles and see if or when the eagles return to the airfield.

By April 2008, researchers caught their first bald eagle: a male sporting a gold band from the National Park Service eagle nest survey from the previous year, which indicated the eagle was a resident of the area instead of a migrant.

This particular male came from a nest on Pig’s Eye Island, just south of the airfield. The young bald eagle, known as “Eagle 66,� was transported to Littlefork, Minnesota near the Canadian border, more than 200 miles away from his nest and released.

The initial results were promising as Eagle 66 stayed within a 30-mile radius of the release site during the spring and summer months. By November, Eagle 66 had began its migration south to its wintering area. Instead of picking up the Mississippi Flyway near Itasca and following it south, Eagle 66 flew southeast to the Duluth area and then south through western Wisconsin before picking up the river at Lake Pepin--well past the airport--before flying on to Iowa.

After spending the winter in the southeast corner of Iowa, Eagle 66 followed the Mississippi River back into Minnesota. But in flying over Pig’s Eye Island, the eagle apparently recognized the area and stopped for the summer.

Conclusions
Even though Eagle 66 is back where he started, it’s much too early to conclude whether relocation does or doesn’t work. Four other eagles still have a chance to give it a go, since the study continues into 2010. Another eagle, Eagle 67, was captured this spring and relocated to northern Minnesota where it spent the summer in Boundary Waters Canoe Area. Perhaps the spring migration of this eagle in 2010 will tell a different story.