Janis K. D. Seegar’s research while affiliated with Virginia State University and other places

Forested shoreline is important perching habitat for bald eagles (Haliaeetus leucocephalus). Measures for perch tree abundance were determined for segments of the Chesapeake Bay shoreline during 1990-1991 to determine the influence of shoreline perch tree availability on the distribution of bald eagles. Shoreline segments used by eagles had more suitable perch trees, a larger percent of forest cover, and greater distances from water to the closest tree (P < 0.01). Differences between used and unused segments appear to be due to the influence of marsh shoreline. Logistic regression models were created to predict the probability of eagle use of the shoreline, given different densities of human development and perch tree availability.

The Chesapeake Bay may once have provided habitat for as many as three thousand pairs of breeding bald eagles and for thousands of subadult and migrant birds. The population has declined dramatically over the past three centuries due to habitat destruction, persecution, and contamination by DDT and other chemicals, reaching a low of 80-90 breeding pairs in 1970. After DDT was banned in 1972, the population began to increase. In 1989, 185 pairs of eagles nested in Maryland and Virginia. Eagles require large trees for nesting, roosting, and perching. These trees must be in areas with limited human activity. Bald eagles are opportunistic predator-scavengers, consuming many different prey species. They take fish when they are available, but shift to waterflow and mammals when fish are scarce. The long-term survival of the bald eagle on Chesapeake Bay will be determined by the management of shoreline habitat. The very rapid rate of shoreline development, if unchecked, will eliminate most large undistributed forest blocks in the next 50-100 years and will lead to a decline and perhaps extirpation of the species from the Chesapeake Bay area. This can be avoided if a series of shoreline refuges is created. Adequate fish and waterfowl populations also will be required to sustain the species in the future.

A study on bald eagle (Haliaeetus leucocephalus) diurnal perching habitat on the north Chesapeake Bay shoreline was conducted from July 1990 to May 1991. The differences between known eagle perch trees and randomly selected trees were investigated. Perch trees were found to be larger than random trees in both diameter-at-breast height and height. Forested shoreline areas had significantly more potential perch trees than either developed or marsh shoreline. Eagles selected marsh habitat less than expected when compared to unused areas.

We studied the influence of shoreline perch trees and human development on bald eagle (Haliaeetus leucocephalus) distribution on the northern Chesapeake Bay. Bald eagle distributions may be determined by available suitable shoreline perch areas. Models based on human development and shoreline habitat variables may alleviate problems associated with classifying bald eagle habitat by identifying characteristics predictive of eagle presence. We observed 2,962 eagles during 36 shoreline surveys and relocated 110 radio-marked eagles 1,350 times during 1985-92. We counted 5,928 suitable (height ≥6.1 m, diam at breast height [dbh] ≥20.0 cm, and shoreline accessibility ≥30°) perch trees in 229, 250- × 50-m segments along shoreline during 1990-91. Shoreline segments used by eagles had more suitable perch trees (x̄ = 30.3 vs. 22.0; P < 0.001) and a larger percentage of forest cover (x̄ = 54.9 vs. 39.4; P < 0.001) than unused segments. Suitable trees on segments with eagle use were closer to water than suitable trees on segments without eagle use (x̄ = 8.4 vs. 17.0 m; P = 0.009). Most segments classified as marsh (66.7%) were unused. Marsh segments had fewer suitable perch trees, less forest cover, and a greater mean distance from water to the nearest suitable perch tree than did other land types (P < 0.001). Developed segments had fewer suitable perch trees, less forest cover, and a shorter distance from water to the nearest suitable perch tree than undeveloped forested segments (P ≤ 0.01). Logistic regression models based on various measures of perch tree abundance and shoreline development correctly predicted eagle use for 65.9-71.0% of segments.

The effects of two radio transmitter attachment techniques on captive and one attachment technique on wild Bald Eagles (Haliaeetus leucocephalus) were studied. A Y-attachment method with a 160-g dummy transmitter was less apt to cause tissue damage on captive birds than an X-attachment method, and loosely fit transmitters caused less damage than tightly fit transmitters. Annual survival of wild birds fitted with 65-g transmitters via an X attachment was estimated at 90-95%. As a result of high survival, only five wild birds marked as nestlings were recovered. Two of these birds had superficial pressure sores from tight-fitting harnesses. It is recommended that a 1.3-cm space be left between the transmitter and the bird's back when radio-tagging post-fledging Bald Eagles. Additional space, perhaps up to 2.5 cm, is required for nestlings to allow for added growth and development.

We examined the role scale plays in determining the predictive power of bald eagle (Haliaeetus leucocephalus) habitat models. We used a bald eagle roost habitat database that included 35 roost sites and 123 random sites located and characterized on the Chesapeake Bay from 1985-1988. A micro-habitat model, based on 6 micro-scale variables, correctly classified 80% of the roost sites. A macro-habitat model, based on 10 macro-scale variables, correctly classified only 63% of the roost sites. A mixed model, incorporating the significant micro- and macro-scale variables, correctly classified 89% of the roost sites. Our results suggest there is a tradeoff between model performance (predictive power), model development costs, and model application.

A study was conducted to quantify diurnal perch habitat and examine the effects of time of day or season on the habitat selection of balt eagles (Haliacetus lencocephalus). An attempt was also made to test the hypothesis that perch habitat differed from habitat available at random on the Northern Chesapeake Bay. A total of 59 bald eagle were radio-tagged, and 220 bald eagle perch trees were identified. Eagles used a greater percent of dead or dead-topped perch trees than expected. No structural differences were found between perches used in May - October and perches used during November - April. These was also no time-of-day effects.

Although studies of bald eagle (Haliaeetus leucocephalus) food habits are numerous, few authors have quantified biases inherent in the techniques used. In our study of food habits of nonbreeding bald eagles on the northern Chesapeake Bay, we examined biases associated with pellet analysis, food remains analysis, and direct observation. We assessed these biases through controlled feedings of 2 captive bald eagles and through observations of free-ranging eagles. Fish fed to 2 captive bald eagles were underrepresented (P < 0.001) in egested pellets. Most bird and mammal food items were detected in ≥1 pellet; however, species and carcass condition affected frequency of occurrence. Analysis of captive eagles' food remains overrepresented birds, medium-sized mammals, and large bony fish (P < 0.001); small mammals and small fish were underrepresented (P < 0.001). This bias increased over time due to greater persistence of some remains in shoreline plots. Direct observations of free-ranging eagles resulted in biases toward easily identified species such as eels and catfish, but also documented the use of small, soft-bodied fish, which were not well documented by the other techniques. Because of the variety of biases present, accurate assessment of bald eagle foods requires use of multiple techniques.

Survival of 39 radio-tagged Haliaeetus leucocephalus in the Chesapeake Bay region was 100% in the first year of life. Mean minimum survival per year of all eagles was 91%, mean maximum survival 98%. A deterministic life-table model predicted a finite growth rate of 5.8% per year; growth rate based on the maximum survival estimates was 16.6% per year. The breeding population actually increased 12.6% per year from 1986-1990. Intrinsic growth rate was 6.9% based on natality and minimum survival data and 19.2% based on maximum survival data. -from Authors