During 2002–05 I monitored a pair of Bald Eagles (Haliaeetus leucocephalus) nesting in Section 41, Township 12 South, Range 13 East, approximately 1 km southeast of Grand Bayou in Assumption Parish, Louisiana. They were not banded, so I am not certain that the birds observed each year were the same individuals.
In Louisiana, Bald Eagles lay eggs between October and mid-March, but most clutches are complete by late December (U.S. Fish and Wildlife Service 1989, Southeastern states Bald Eagle recovery plan, U.S. Fish and Wildlife Service, Atlanta, GA U.S.A.). During the first two breeding seasons I observed, the pair began incubation on 9 December 2002 and 10 December 2003, respectively. During the 2004–05 breeding season, this pair initiated incubation on 10 December 2004.
On 21 December 2004, I observed the Bald Eagles with 7 × 35 binoculars from an observation point that afforded an excellent view of the nest and two habitually-used perch trees. The observation site was situated approximately 213 m northwest of the nest and 152 m southwest of the primary perch tree.
At 0915 H, an adult Bald Eagle was perched on the primary perch tree. At 0920 H, it flew toward the nest. Approximately 116 m south of the perch tree, it flew feet first into a dead baldcypress (Taxodium distichum). The impact was audible from my observation point ca. 110 m away. The Bald Eagle fluttered against the side of the tree for approximately 3 sec, at which point it folded its wings and commenced a free fall. I heard a ripping sound as bark was stripped off the trunk. The bird then resumed its flight toward the nest. The Bald Eagle deposited the bark in the nest and relieved its mate from incubation duty. At 0925 H, its mate flew from the nest to the primary perch tree.
I later measured the stripped area of the tree with a clinometer. The bark strip obtained was 1.5 m long.
I speculate the bark was used as nest lining. The observation occurred during the second week of incubation. Baldcypress bark is limp and fibrous. With daily use as described by Herrick (1932, Auk 49:307–323), bark would likely deteriorate to loose fibers. Palmer ([Ed.] 1988, Handbook of North American birds, Vol. 4, Yale Univ. Press, New Haven, CT U.S.A.) lists similarly textured nest lining material in eagle nests. Brown (1955, Eagles, Michael Joseph Ltd., London, U.K.) suggested greenery gathered during incubation is used ultimately as nest lining.
This is the first report to my knowledge of a Bald Eagle obtaining nest material by stripping bark from a tree. Bald Eagles typically gather nest material from the ground (Bailey 1919, Wilson Bull. 31:52–55, Herrick 1932, Palmer 1988)or break branches from trees (Buehler 2000, in A. Poole and F. Gill [Eds.], The birds of North America, No. 506. The Academy of Natural Sciences, Philadelphia, PA and The American Ornithologists' Union, Washington, DC U.S.A). I have observed this pair of Bald Eagles gather clumps of aquatic grasses from the ground and take them to the nest. Baldcypress bark sloughs profusely from dead or dying trees, and is abundant on the ground in the study area. I had previously observed them carry bark strips to the nest, but assumed the bark was gathered from the ground. Occasionally, Bald Eagles fly into and break branches from trees for use in nesting (Palmer 1988). Bailey (1919) described a Bald Eagle hovering approximately 8 m over a branch, then diving downward to snap the branch from the tree.
I thank Gulf South Pipeline Company, Limited Partnership, for the opportunity to monitor this pair of Bald Eagles for three breeding seasons. I gratefully acknowledge J. Watson, R. Jackson, and J. Bednarz for their constructive criticisms of the manuscript.