The influence of thorny elaeagnus on automobile-induced bird mortality
Thorny Elaeagnus (Elaeagnus pungens) has been used throughout the southeastern United States as a highway median plant for more than 30 years. Native to Asia, elaeagnus has a number of characteristics that make it ideal for roadside planting. The plant is a heat and drought resistant, evergreen shrub that is fast growing. Because elaeagnus forms a dense, tall hedgerow, it provides an effective divider between opposing lanes of traffic. In the spring of 1999, representatives of the U.S. Fish and Wildlife Service collected 459 dead birds along discreet sections of highway near Richmond, Virginia. Roadway sections were adjacent to median plantings of thorny elaeagnus containing dense fruit crops. The objective of this field study was to investigate the possible relationship between median plantings and bird mortality. A simple one-way study design was used with median condition as the single factor. Three median conditions were examined including (1) no median planting, (2) elaeagnus without fruit, and (3) elaeagnus with fruit. Replicate roadway segments containing desired median conditions were surveyed 3 times/week for live and dead birds from mid-March to mid-May. The presence of ripe elaeagnus fruit had a significant influence on both the use of medians by birds and bird mortality. Of 1,270 live birds observed along the roadways, 1,200 were detected along plantings that contained dense fruit crops. These same roadway sections accounted for 78 of 80 dead birds collected. Bird density and mortality within medians that supported shrubs without fruit were not appreciably higher than control medians that contained only grass. Additionally, the seasonal timing of median use and mortality was found to correspond to the peak availability of ripe fruit. Finally, the composition of live and dead birds was dominated by fruit-eating species. The results of the study suggest that birds are attracted to elaeagnus fruit within median plantings and that mortality is a consequence of this attraction. The juxtaposition of dense fruit crops with high-traffic areas seems to result in elevated bird mortality. Birds are being struck and killed by oncoming traffic as they fly across roadways to reach fruit crops.