Nesting Bald Eagles

by John S. Castrale

Indiana Department of Natural Resources, Mitchell, IN

The return of the bald eagle from the brink of extinction in the lower 48 states represents one of conservation’s most notable success stories. The recognition that the pesticide DDT was to blame for the eagle's precipitous decline and quick action to ban its use in North America during the early 1970's was largely responsible for saving the bald eagle from oblivion. Other measures to protect bald eagles were also instrumental in increasing the numbers of eagles. The Migratory Bird Treaty Act, the Bald Eagle Protection Act, and the Endangered Species Act all imposed penalties for eagles being shot, poisoned, harassed or otherwise harmed, with protection extending to their eggs and nests. The Endangered Species Act also insured that projects undertaken or funded by federal agencies did not jeopardize bald eagles and habitats considered critical to them. Government agencies also developed management guidelines to ensure successful reproduction of eagles on public and private lands. As a result of these actions, the U.S. Fish and Wildlife Service recently changed the legal status of the bald eagle from endangered to threatened.

In some states, including Indiana, restoration in the form of releasing young bald eagles taken from distant nests, has had a major impact on the number of eagles breeding in local areas. During the 1985-1989 period, the Nongame Program of the Indiana Department of Natural Resources released 73 12-week-old eagles at Lake Monroe with the hope that when they reached maturity in 4-5 years, they would return to south-central Indiana, find a mate, and nest. This has occurred and from the first breeding attempt in 1989, the nesting population has grown to 15 pairs during 1996. Prior to this recent nesting activity, bald eagles had not been documented breeding in Indiana since before 1900.

So what does this mean to landowners and timber operators, who may find that a pair of bald eagles has built a nest in a forested tract? With the reauthorization of the Endangered Species Act now being considered by Congress, much misinformation is being put forth about endangered species in an effort to drastically weaken this important legislation. The purpose of this article is not to address all the issues that have cropped up, but to relate how nesting bald eagles are managed in Indiana. Although the U.S. Fish and Wildlife Service has the ultimate responsibility in dealing with eagle issues, the Indiana Department of Natural Resources has played an active role working with landowners and land managers to maximize the chances that eagles will nest successfully.

To put things in perspective to a landowner who is concerned that a bald eagle will take up residence on his or her properly, consider the possibility of that happening. With only 15 pairs in the entire state, eagle nesting is a rare event. All birds released at Lake Monroe have now become mature and should already be in the breeding population, so increases from past Indiana releases should not add additional pairs. Eagles released or raised in other states are nesting in Indiana, but only two pairs in the state are made up entirely of these immigrants. Because birds tend to nest in areas near where they were raised, we don't expect significant increases in pairs from these sources. The future of eagle populations in Indiana will primarily depend upon successful reproduction and survival of young from the small core population that now exists. This population should slowly grow, but it is difficult to estimate the total numbers of bald eagles the state can support. With the relatively small amount of forested land in close proximity to large bodies of water or extensive marshes, Indiana will never have a large number of summering bald eagles.

To further assess the potential for bald eagles nesting in a specific location, it is helpful to examine the geographical area, general habitat and micro-sites currently being used by bald eagles in Indiana. Recent nests have been located in 9 Indiana counties, all in the southwestern quarter of the state, and mostly concentrated in south central Indiana. All current Indiana nests, with one exception, are within 50 miles of the release site at Lake Monroe. Most future nests will likely be found in his region of the state, although it would not be too surprising to discover a nest in extreme northeastern Indiana, at Brookville Reservoir, or in some counties bordering the Ohio or lower Wabash rivers.

Eagle nests are associated with forested areas near larger bodies of water where fish, waterfowl, turtles, and other foods are obtained. Eleven of the 15 Indiana nests are near the shorelines of larger impoundments, only 2 on private land. Lake Monroe has 3 nests, Patoka Lake hosts 2 pairs and Cagles Mill Lake has a single pair, although a second nesting area once present has been abandoned. The smallest lakes with an eagle pair are about 100 acres in size, and, in these cases, adjacent rivers and lakes are likely important for finding adequate food. Four nests are along shorelines of larger rivers, including the East and West Forks of the White River and the Wabash River; all are on private land. Small streams are not suitable for eagles. Nesting areas on lakes generally have extensive forested areas surrounding them, while those on rivers in Indiana consist of a narrow band of Iowland woods bordering agricultural fields.

Eagle nests are generally placed near shorelines and a pair may have more than one nest that may be used in subsequent years. Where human disturbance is great or large trees are not available, nests may be located 1/4 mile or more from the water's edge. The availability of suitable trees is another important criteria influencing nesting. Trees must be relatively large to support the massive nest that is placed high in the tree near the main bole at a major fork. All nest trees used by Indiana eagles are deciduous trees and only one is in a snag. A variety of tree species have been used: oaks, cottonwood, sycamore, ash, aspen, and silver maple. The tree species is less important than its size, structure, and location relative to water. Because bald eagles have large wingspans and do not maneuver well through forests, easy access to the nest tree is important. Nests are placed in a major tree crotch just below the upper canopy and nest trees generally extend above adjacent trees, or are situated along the shoreline, at a woodland edge, or along the top or mid-slope of a ridge. One Indiana nest tree was likely selected because previous timber harvesting resulted in improved access.

The 15 Indiana nests are on lands owned or managed by: the Indiana Department of Natural Resource (5 nests), Indiana University (1), the U.S. Department of the Navy (2), the U.S. Forest Service (1), a private lake association (1), and private individuals (5). In all cases where a nest is discovered, the landowner or land manager is contacted and ways to ensure successful nesting are discussed. Management for successful nesting centers on two factors: minimizing disturbance during the nesting season and maintaining the nest tree and adjacent habitat. In considering disturbance sources, we examine what activities are present or may occur during the breeding season which may extend from mid-February to mid-August. On lakes with recreational use, buoys are usually placed around the nest to maintain a minimum distance between the nest and boaters. Short segments of trails may be closed to prevent close approach by land. Two nests have been located in close proximity to county roads. In one case, county commissioners agreed to close the road during the breeding season. In another case, the road remained open because traffic was light and consistent throughout the year and the pair showed tolerance of occasional vehicles. Normal farming operations are not prevented, although farmers are encouraged to avoid stopping near the nest tree or favored perches while eagles are present.

Because eagles nest in trees, timber cutting is of concern. Forest clearing for housing or other developments has the most negative consequences for bald eagles, but timber management in an area can proceed with consideration given to the distance from the nest and timing of activity. Public land agencies exclude areas around eagle nests from their timber harvest plans. Cuts on more distant areas are allowed, although timing of timber management is delayed until after the breeding season. Retention of super canopy trees is desirable in providing trees for alternate nests. There have been few conflicts with private landowners. Most place great value in having eagles on their property and are more than willing to accommodate them. In many cases, nest trees are overmature, have poor form, are of Iow value, or the more valuable timber has been previously harvested. Selective cutting of trees can be done in such a way to still maintain eagle habitat.

Management around eagle nests in Indiana is on a case by case basis and has consisted of using a common sense approach that assesses present and prior uses near the nest. Because eagles sometimes select a nesting area that may have relatively high human use, they are given a chance to nest without undue constraints on landowners and users. The philosophy has been to minimize restrictions and determine if eagles can nest successfully under those conditions. If nesting failures appear to be due to human activities, further steps can be tried. This approach appears to be working as nesting success has been high (around 80%) the past couple of years and human disturbance has rarely been implicated in nesting failures.

The more traditional approach to management of eagle nesting areas consists of zones around nests and is presented here to give readers an idea of the tolerance of eagles to different activities. These are general guidelines that have been developed to ensure successful nesting by eagles but each pair may react somewhat differently, and topography and visual screening will affect the distances given. These guidelines specify three zones around a nesting tree with fewer restrictions in zones farthest from the nest tree. The primary zone extends 330 feet from the nest tree and any land clearing, timber cutting, and building of roads or trails is discouraged. Human disturbance should not be allowed during most of the nesting season (mid-February to mid-July). A secondary zone ranges to a distance of 660 feet from the nest and human disturbance should be minimized during the breeding season. Significant changes in the landscape should be avoided, although timber stand improvement and other activities are possible outside the nesting season. A third zone that extends up to 1/4 - 1/2 miles from the nest, depending on topography and line of sight to nest, permits most activities outside the breeding season.