Abstract
Eagles are protected under the Endangered Species Act (ESA), Bald and Golden Eagle Protection Act, the Lacey Act, as well as the Migratory Bird Treaty Act. States also protect eagles through state threatened and endangered species laws. National efforts to protect eagles have focused on habitat conservation, minimizing contaminant effects, monitoring wild bird nests, and coordinating captive propagation and release programs. Bald eagle (Haliaeetus leucocephalus) and golden eagle (Aquila chrysaetos) populations are growing in the USA. The Chesapeake Bay is home to hundreds of nesting pairs of eagles. Currently, eagles are listed as threatened in Maryland.
Four organizations work collaboratively on eagle morbidity and mortality in our region. The Maryland Department of Natural Resources (MD DNR) and U.S. Fish & Wildlife Service (FWS) serve as regulating and permitting agencies. Tri-State Bird Rescue and Research and the Baltimore Zoo are the two facilities permitted to conduct treatment and rehabilitation for eagles. Carcasses of eagles that die or are found dead in Maryland are transferred to FWS and frozen for eventual shipment either to the National Eagle Repository or the FWS Forensics Laboratory.
To examine eagle mortality in Maryland, databases from the four organizations were reviewed. Minimal information existed on cause of death for Maryland eagles prior to 1988, so the period examined begins with January 1988 and extends through March 2004. A total of 220 eagles were found dead or died in Maryland during the study period with an average of approximately 14 deaths per year (range 2–29).
For all eagles, causes of death included:
- 63 traumatic injuries:
- Collision (34)
- Other physical trauma (29)
Other causes of death included:
- Electrocution (32)
- Poisoning (23)
- Drowning (9)
- Disease (5)
- Entanglement (3)
- Gunshot (5)
- Unknown causes (80)
Little is known about eagles in the unknown category other than the date and location of the incident. Legal cases are still open, and no information is available until the cases are settled.
However, the majority of eagles in the unknown category had no cause of death information listed.
The databases were reviewed for temporal and spatial significance. Three separate years (1988/28, 1997/22, 2003/29) accounted for nearly one-third of the total number of eagle mortalities. No other clusters of mortalities were found in the period examined; however, an overall increasing trend in mortalities was noted. From a geographic perspective, eagles were reported dead in 21 of 23 counties in Maryland. The majority came from three counties: Charles (34), Harford (34), and Dorchester (31) accounting for nearly half of all mortalities reported (99/220). Since these counties are located in different regions of the state, the mortalities did not represent a geographic concentration. Additionally, 124 eagles were identified as adults, 72 as immature, and 24 were not identified by age.
The primary objective in this study was to examine the causes of eagle mortality in Maryland. Results indicated that eagles died throughout most counties of the state over the entire study period for a variety of reasons. However, the majority died from unknown causes. Through our cooperative efforts, we hope to better identify causes of eagle mortality that will lead to identification of threats and impacts to Maryland populations. This collaboration will serve as a model for future wildlife investigations and conservation efforts in our region.