REPRODUCTIVE SUCCESS OF BALD EAGLES

(HALIAEETUS LEUCOCEPHALUS) NESTING IN THE 

VICINITY OF THE CHALK POINT OIL SPILL

Final Report

April 11, 2001

Introduction

On April 7, 2000 an underground pipeline transporting a mixture of #2 and #6 fuel oil to the Chalk 

Point PEPCO plant located near the town of Aquasco, in Prince George’s County, Maryland ruptured. 

 The fractured pipeline released approximately 126,000 gallons of product into a Spartina spp. 

dominated brackish wetland located in Swanson Creek, a tidal tributary of the Patuxent River. 

Extensive oiling of the wetlands within Swanson Creek took place during the first two days of the spill. 

In addition, high winds with gusts in excess of 50 mph passed through the area on April 8 and 9, 

resulting in oil escaping from Swanson Creek and entering the mainstem of the Patuxent River and 

several of its tributaries. Primary habitats impacted during the spill were wetlands, sandy beaches and 

open water areas associated with these habitats. Several avian species that are dependent on aquatic 

habitats were nesting in the area at the time of the spill, including osprey (Pandion haliaetus), federally 

threatened bald eagles (Haliaeetus leucocephalus), and great blue herons (Ardea herodias). The 

foraging strategy of these species and willingness to enter water and wetlands make them susceptible to 

oiling. Several oiled osprey and great blue herons were observed by wildlife survey teams during the 

response effort. 

The Natural Resource Trustees for the Chalk Point Oil Spill were concerned about the potential effects 

of the oil spill on the reproductive success of these avian species. To this end, the objective of the 

present study was to evaluate the potential effects of the oil spill on the nesting success of bald eagles. 

Other reports describe results of monitoring nesting great blue herons and osprey.

Study Organism and Susceptibility to Oiling

The bald eagle is the largest raptor species found within the Patuxent River region, with 12 nesting pairs 

documented along the river and its tributaries in 2000 (Glenn Therres, Maryland Department of Natural 

Resources, personal communication). Bald eagles are a species vulnerable to oil spills because of their 

dependence on aquatic habitats for foraging. Shallow water areas with abundant fish, followed by 

wooded shorelines, and extensive marshes are key habitat elements required by bald eagles (Robbins 

and Blom, 1996). Many of these habitats were observed to be oiled during the Chalk Point spill. Bald 

eagles feed exclusively on fish when they are abundant. During times of low fish abundance, bald eagles 

will prey on waterfowl and scavenge carcasses taken from the water and along shorelines. During an oil 

spill, foraging eagles may become directly contaminated with oil or feed on contaminated prey.
Adults that become oiled may transfer the oil from their plumage to their eggs during incubation. 

Refined oil may be highly toxic to avian embryos depending on the species; stage of embryonic 

development; and type, weathering, and dose of oil. Small quantities of oil on eggs can lead to embryo 

mortality, or cause deformities, especially during the early incubation phase (Albers 1991, 1995, 

Hoopes et al. 1994). Studies have shown that as little as 1-20 uL of some types of oil can have lethal 

effects on developing embryos (Parnell et al. 1984, Hoffman 1990). Louisiana heron (Hydranassa 

tricolor) eggs treated with 10 uL of weathered crude oil had a reduced hatchability of 17% (Macko 

and King, 1980). In addition, the oil spill may have reduced or contaminated prey species, such as fish 

and waterfowl, with subsequent effects on reproductive success. Several studies have reported 

reproductive effects on avian species due to dietary exposure to petroleum-derived products (Coon and 

Dieter 1981, Ainley, et al. 1981). Finally, human disturbance related to cleanup activities has been 

shown to impact the reproductive success of bald eagles. During the 1989 Exxon Valdez spill in 

Alaska, bald eagles nesting in oiled areas with high cleanup activities had low reproductive success with 

only 200 young being produced. In 1990, in the same area, cleanup activities were reduced and greater 

than 1,000 young eagles were produced (Baker et al., 1991). 

Because bald eagles are susceptible to human disturbance, especially during the nesting season, 

attempts were made to minimize this stress during the Chalk Point oil spill. The U.S. Fish and Wildlife 

Service (USFWS) requested on April 10 that the Federal On-Scene Coordinator contact the Federal 

Aviation Administration and establish a no-fly zone around the two bald eagle nests within Swanson 

Creek. Because no bald eagles were known to nest along the eastern shoreline of the Patuxent River, 

the USFWS also recommended that daily aerial surveys of the Patuxent River be conducted from along 

the eastern shoreline of the river rather than along the western shoreline. The no-fly zone included a 

0.25 mile radius around each nest, and a minimum of 1,500 vertical distance above each nest. These 

guidelines were based on recommendations from USFWS law enforcement agents and Maryland 

Department of Natural Resources (MDNR) Wildlife and Heritage personnel.

Methods

Study Area

Two active bald eagle nests were located within Swanson Creek, a third nest active nest was identified 

near Cremona Creek, approximately 7.0 miles downstream of the spill release. The nests were 

identified as: Stanley Run, Swanson Creek, and Cremona Creek. All three nests were determined to be 

active during the first week of the spill. On April 9, the Chalk Point Natural Resource Trustee Council 

determined that PEPCO personnel with the assistance of the USFWS would monitor the three active 

nests for reproductive success on a regular basis until young had left the area.

Results

Stanley Run

This nest was located in a large red maple (Acer rubrum) tree located on PEPCO’s property near 

Stanley Run. The nest had been active for approximately 5 years previous to the spill (based on 

observations during wood duck monitoring by PEPCO personnel). On April 11, USFWS personnel 
observed, from the ground, one nestling and an adult female. Both birds appeared to be normal, based 

on behavioral observations. The USFWS estimated the nestling was approximately 12 days old. On 

April 13, USFWS personnel climbed the nest and documented the presence of two eaglets 

approximately 4 weeks old. 

On May 2, the nest was revisited by USFWS personnel, including Law Enforcement, and a PEPCO 

representative, with the intention of banding the young. Upon arrival to the nest site it was observed 

that the nest had been destroyed, presumably by high winds that were experienced earlier in the week. 

The banding team picked through the nesting material and broken branches and found feather sheathings 

from the young. Based on the development of the feathers, USFWS personnel concluded that the nest 

had fallen soon after the visit on April 13th. Samples of the sheathings were collected and maintained 

by the USFWS. As a result of the nest destruction, the nest was eliminated from the reproductive 

monitoring study.

Swanson Creek

The second nest identified within the vicinity of the spill was located in a Virginia pine (Pinus 

virginiana) tree near the mouth of Swanson Creek in Charles County. The nest had been observed 

during an earlier field reconnaissance conducted by USFWS Law Enforcement agents. USFWS Law 

Enforcement agents noted that a pair of birds had been hanging around the nest and were acting 

abnormally. Based on the behavior exhibited by the birds it was thought that there were eggs or young 

present at that time. On April 16, USFWS personnel climbed the nest and found no evidence of young 

or eggs. However, it was noted that the nest had been somewhat active based on the linings of the nest 

with feathers. The USFWS concluded that the nest belonged to a young pair of eagles and the nest had 

failed naturally. This nest, like the Stanley Run nest, was removed from the reproductive monitoring 

study.

Cremona Creek

This nest was located on a farm in Cremona, MD (St. Mary’s County) approximately 7 nautical miles 

south of Swanson Creek. The nest was located in a large sycamore (Platanus occidentalis) on the 

edge of an active farm field about 5,000 feet inland. The nest was observed from the ground by 

USFWS and PEPCO personnel on April 20. The observations revealed that two nestlings were 

present. The nest was revisited by USFWS and PEPCO personnel on April 24. At this time the nest 

was climbed by USFWS personnel, and the nestlings banded. It was noted by the USFWS that the 

coloring of the eaglets was “a little off’. 

Regular monitoring was initiated May 17 and continued until October 16. Monitoring was conducted 

from the ground using binoculars. All observations were made within a 10 minute time frame. The 

following observations were recorded: number of young and adults present, each bird’s location with 

respect to nest, and any unusual circumstances. 

The two eaglets that were observed in the Cremona nest initially on April 20 were observed in the nest 

until June 6, which was also the first time they were seen off the nest. From this date on, the eaglets 

were always observed to be within 30 feet of the nest, this behavior continued until the third week of 
September. On September 27, which was the last time the eaglets were observed, the juvenile eagles 

were seen some distance from the nest across an adjacent field. The last time an adult eagle was 

observed was October 2. Table 1 provides a summary of observations noted during the monitoring 

period. 

Table 1. Summary of Cremona Creek bald eagle monitoring data

May 17 both young, both adults

May 25 both young, one adult

May 31 both young, both adults

June 6 both young (one off nest), one adult

June 14 both young, didn’t see adults

July 10 both young (one off nest), no adults

July 20 both young off nest, no adults

August 8 both young off nest, no adults

August 23 both young off nest, both adults

September 6 no young, one adult

September 27 both young in field away from nest, no adults

October 2 one adult

October 16 none 

Conclusion

Based on the observations conducted by USFWS and PEPCO personnel, there were no apparent 

effects of the oil spill on the Cremona Creek bald eagles. The Cremona Creek eagles successfully 

fledged 2 eagles in 2000. The average number of young per breeding pair in this study was 1.0 

(assuming breeding pairs at Cremona and Stanley Run), a value above the 0.7 young per breeding pair 

thought to be required to maintain a stable population within the Chesapeake Bay region (USFWS 

1990). In addition, this value approaches the recovery target of 1.1 young per breeding pair established 

by the Chesapeake Bay Region Bald Eagle Recovery Team (USFWS 1990). 

Acknowledgments

This study was conducted under the direction of the Wildlife Injury Workgroup for the Chalk Point 

Natural Resource Damage Assessment Council. The Wildlife Injury Workgroup members are: Beth 

McGee and Peter McGowan, USFWS Chesapeake Bay Field Office; Mark Hoffman, Maryland 

Department of Natural Resources; Jacqueline Michel, Research Planning, Inc., and Richard Greer, 

Entrix, Inc., representing PEPCO. The report was prepared by Ann Wearmouth (formerly of PEPCO) 

and Peter McGowan (USFWS). We are extremely indebted to Craig Koppie (USFWS) for climbing 

the nests and making initial observations. Ann Wearmouth conducted the long-term monitoring of the 
Cremona Creek eagles. 
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