a steppe eagle nest in extreme northwestern Mongolia comprised mostly of long bones of domestic animals. It also contained an iron piston rod, a 30-cm section of a hay mowing sickle bar, a rubber fly swat and a flattened metal food can.
On four expeditions (1994, 1995, 1997 and 1998) through Mongolia, David H Ellis of the USGS Patuxent Wildlife Research Center, Maryland, usa , and James W Lish of the Oklahoma State University College of veterinary Medicine, Oklahoma, usa , found many such nests made up of trash gathered by birds as part of the nest-building process (Ambio , Vol 28, No 6).
The scientists have reported two kinds of mortality associated with the raptors - though observations were limited to only three species, the golden eagle ( Aquila chrysaetos ), the saker falcon and the upland buzzard. The first was death due to entanglement.
For instance, on July 1, 1995, a 35-day-old nestling was found with coarse gauze twisted around its legs. Used by the nomadic herders to strain milk and thereafter discarded, gauze fabric is common in raptor nests in Mongolia. During the process of collecting nesting materials, the wide fabric is very often stretched and folded into a narrow band that can snare a leg.
The second cause of death involved abandoned golden eagle eggs after they were concealed by trash, presumably brought as nestling materials by the adults. On June 3, 1998, the scientists came across a single leaking egg under a thin layer of plastic and paper.
Across much of Mongolia, trees and perennial shrubs are rare. Therefore, raptors use cloth, bones, paper, wire and twine as primary components of their nests. However, it has been noted that the use of trash is not essential because raptor nests in areas far from human habitation normally have no trash.