I studied bald eagle (Haliaeetus leucocephalus) distribution, abundance, roost use and response to human activity on the northern Chesapeake Bay from 1984-89. The eagle population consisted of Chesapeake breeding eagles, Chesapeake nonbreeding eagles, northern-origin eagles and southern-origin eagles; changes in overall eagle distribution and abundance reflected the net changes in these 4 groups. Breeding territories on the northern Chesapeake increased from 12 to 28 from 1984 to 1988. Breeding eagles were resident all year, always ~7 km from the nest. Chesapeake nonbreeding eagles moved throughout most of the bay, but rarely left it (~5% of the radio-tagged eagles were off the bay during any month). Northern eagles migrated into the bay in late fall (x = 21 December! n = 7! range = 61 days) and departed in early spring (x = 27 March, n = 14, range = 43 days). Southern eagles arrived on the northern bay throughout April-August (x = 6 June, n = 11, range = 94 days) and departed from June - October (x = 3 September, n = 22, range = 119 days). Northern Chesapeake eagle abundance peaked twice annually; in winter (261 eagles, December 1987), driven by the presence of northern eagles, and in summer (604 eagles, August 1988), driven by the presence of southern birds. Of 1,117 radio-tagged eagle locations, only 55 (4.90/0) occurred in human-developed habitat, which composed 27.7% of 1,442 km2 of potential eagle habitat on the northern Chesapeake Bay (P < 0.001). During 36 aerial shoreline surveys, eagles were observed on only 111 of 700 (15.9%) 250-m shoreline segments that had development within 100 m, whereas eagles were observed on 312 of 859 (36.30/0) segments when development was absent (P < 0.001). On average, eagles were observed on 1.0 segment/survey that had coincident pedestrian use within 500 m, compared to 3.6 segments/survey expected if eagles and pedestrians were distributed along the shoreline independently (n = 34 surveys, P < 0.001). / Ph. D.

I examined the roosting and perching habitat preferences of a nonbreeding population of bald eagles in North Carolina during 1986 and 1987. I characterized roosting habitat at 2 scales; those of forest stands and individual roost trees. Eagles chose roost areas that were less dense, had less canopy cover, were closer to forest edges, and had larger trees than random forest areas (P < 0.05). Within roost areas eagles choose trees that were larger (height and dbh) than random trees. Additionally. eagles roosting at the Morgan Creek roost preferred dead hardwoods close to the forest edge and eagles at the Mason Point roost preferred trees farther from a frequently used dirt road within the roost. Suitable perch trees were the most important attribute of perching habitat. Eagles preferred loblolly pines and trees with leafless crowns (P < 0.05), which relates to their accessible crown structures. Perch trees were larger (height and dbh, P < 0.05) than adjacent trees along the shore. Eagles utilized the bottom of tree crowns during summer but used treetops during fall and winter. I found no evidence that eagles selected perches in relation to forest stand characteristics within 20 m of perch trees, forest cover types in 1 ha blocks surrounding perches, or habitat disturbances. Management recommendations include techniques to enhance bald eagle habitat on the study area. Primary emphasis should be toward managing for roosting habitat because of its apparent scarcity. Perch trees are plentiful but long-term management is desirable. Future nesting seems likely and management techniques for potential nesting habitat are suggested. / Master of Science

I studied the effect of human activities on bald eagle (Haliaeetus leucocephahus) distribution and abundance at Jordan Lake and Falls Lake, North Carolina in 1986 and 1981. Eagles used most of the area available on Jordan Lake, but 63% of the use occurred in the northern 25% of the lake. Eagle use at Falls Lake was restricted to a few areas in the northern section of the lake. Jordan Lake had 1.2 times as many eagle observations as did Falls Lake. Data from radio-tagged eagles and timing of population fluctuations suggest that eagle populations at Jordan and Falls Lakes were principally migrating eagles from southern states. The peak in eagle numbers in May 1981 may have represented a migratory wave, whereas the decrease in June and July may have been the result of some eagles continuing northward. Eagles returning south from the Chesapeake Bay and other northern areas may account for the slight increase observed in August. Two eagle roosts were located and monitored throughout the study at Jordan Lake. Human activities at both lakes peaked during summer months. Boating was the predominant activity during summer. Sixty-three intentional disturbances by motor boats produced a mean eagle flush distance of 131.2 m. Only 8% of the eagles flushed when the approaching boat was > 250 m from shore. Loglinear analysis revealed that human use of the shoreline and eagle use of the shoreline were related. Shoreline segments (250 m) used by humans were used less frequently by eagles than would be expected under a model of complete independence. I saw more eagles and fewer humans on weekdays than on weekends during boat surveys of selected Jordan Lake sections, suggesting that human use in certain sections on weekends displaced eagles. The lake section north of the Farrington Bridge showed the largest difference between eagle numbers on weekdays versus weekends. I developed a regression model that predicted the threshold density of disturbance Within this section to be 0.5 boats/km². On most days during the summer, this threshold level of boating traffic is surpassed in lake sections south of the Farrington Bridge. Primary management objectives should be to reduce human activities within high-eagle use areas, specifically the northern end of Jordan Lake, and to promote the bald eagle as a recreational benefit rather than a management problem. / Master of Science

Availability of dead fish to bald eagles (Haliaeetus leucocephalus), prey preferences of bald eagles, and the effects of food on their distribution and movements on the northern Chesapeake Bay were examined from April 1988-July 1989. Dead fish surveys were conducted, by boat, to monitor dead fish availability in several eagle-use areas of the northern Bay, and 3 methods were used to describe disappearance rates of dead fish: dead fish cages, anchored dead fish and floating dead fish. Live fish availability was monitored using gillnets. Dead fish were most available to eagles from May through September, with a peak in availability in June (0.75 dead fish/km with fish die-offs not included, and 3.5 dead fish/km with fish die-offs included). Channel catfish (Ictalurus punctatus) comprised the largest portion of dead fish in early summer months (30% and 28% of total seen, excluding fish die-offs). In contrast, live catfish comprised only 0.4% and 2.1% of the fish caught near the surface in gillnets during spring and summer indicating that dead catfish may be more available, relative to other species, than live catfish. Atlantic menhaden (Brevoortia tyranus) comprised 83-98% of the fish seen in 2 fish die-offs (175 total fish). Only 2 dead fish were seen along 147.7 km of dead fish surveys in winter (0.014 dead fish/km). Most (95%) dead menhaden that we anchored near the bottom off Aberdeen Proving Ground (APG) in summer were scavenged before becoming rancid (X̅= 0.4 days). In contrast, 70% of dead menhaden that we put out in winter became rancid before being scavenged (X̅= 9 days). Pairs of prey items were offered on shoreline areas to wild bald eagles and on platforms to 2 captive bald eagles. All pair-wise combinations of channel catfish, gizzard shad (Dorosoma cepedianum), menhaden and white perch (Morone americana) were offered. We also paired gizzard shad with mallards (Anas platyrhynchos) and rabbits (eastern cottontails, Sylvilagus floridanus, or domestic rabbits, Oryctolagus cuniculus) in shoreline trials, and gizzard shad with mallards and eastern gray squirrels (Sciurus carolinensis) in captive eagle trials. Wild and captive eagles preferred catfish (P=0.0072 and P<0.0002, respectively), and showed no preference for gizzard shad, menhaden nor white perch. Wild eagles preferred gizzard shad over mallards in summer and in winter (P= 0.062 and P=0.002, respectively), while captive eagles preferred mallards over gizzard shad (P= 0.039). Wild eagles selected gizzard shad 4 of 4 times over rabbits (P= 0.125), while captive eagles selected squirrels 5 of 5 times over gizzard shad (P=0.062, both eagles combined). Handling time and familiarity with prey seem to be major factors influencing prey preference, though prey availability seems to determine the actual diet of eagles on the northern Bay. The prediction that the autumn decline in fish abundance on the northern Chesapeake Bay causes eagle distribution to shift from APG to 2 autumn/early winter concentration areas on the northern Bay (Susquehanna River and the Eastern Shore) and then to Blackwater National Wildlife Refuge (BWNWR) and vicinity (winter concentration area on the lower Bay) was tested. By supplying fish (mostly gizzard shad) ad libidum each morning at 2 sites from 28 September through 11 December 1988 a situation in which fish availability did not decline on APG was simulated. Eagle use of the sites increased from 4 eagles seen on first morning that we supplied fish to a peak of 63 eagles seen on the morning of 8 December. Based on shoreline surveys and relocations of 39 radio-tagged nonbreeding Chesapeake hatched eagles, eagle distribution shifted to the Susquehanna River, where eagles feed on gizzard shad, as in 1986 and 1987. However, they did not shift to the Eastern Shore to feed on waterfowl as they had done in 1986 and 1987. Supplemental feeding on APG failed to keep eagles from moving to the lower Bay. Although local eagle distribution on the northern Bay in autumn seems to be dependent on food availability, the autumn decline in fish abundance may not be the proximate factor causing movement to BWNWR and vicinity. / Master of Science

The subsidized island biogeography hypothesis proposes that nutrient subsidies, those translocated from one ecosystem to another, can indirectly influence species richness on islands by directly increasing terrestrial productivity. However, the lack of a formal statistical model makes it difficult to assess the strength of the hypothesis. I created a formal subsidized island biogeography model to determine how nutrient subsidies, in addition to area and distance from mainland, influence tree species richness. My model showed that an increase in terrestrial nitrogen abundance results in a decrease of tree species richness. Soil and plant δ 15N values were higher than expected and it is likely that nutrient subsidies from the marine environment are responsible for 15N enrichment. However, the range of observed nitrogen abundance is similar to inland coastal-zone forests, indicating that islands are similarly nitrogen deprived and may not be receiving enough nutrient subsidies to alter productivity. Tree species decline may therefore be more strongly related to the environmental conditions leading to patterns of nitrogen abundance rather than the abundance of nitrogen itself. Additionally, I proposed that bald eagles (Haliaeetus leucocephalus) are vectors of nutrient subsidies, depositing nutrient-rich guano at nest sites, which could alter soil chemistry and vegetation composition. In an exploratory study of seven nest sites, I found higher soil phosphorous at eagle nest sites relative to control sites (~ 33% higher). Phosphorous is a limiting nutrient in coastal temperate forests, additions help to alleviate chlorosis and slow growth especially when paired with nitrogen. Higher potassium concentration also occurred on eagle-inhabited islands but was not associated specifically with current nest sites, perhaps reflecting differential persistence of macronutrients in the soil. Despite expectations, soil δ 15N abundance was not statistically higher at eagle nest sites. Total soil nitrogen was also not statistically higher at eagle nest sites. There were no significant differences between vegetation composition at eagle nest sites and reference sites, but reference sites tended to be dominated by shrub species. Additionally, I proposed that bald eagles (Haliaeetus leucocephalus) are vectors of nutrient subsidies, depositing nutrient-rich guano at nest sites, which could alter soil chemistry and vegetation composition. In an exploratory study of seven nest sites, I found higher soil phosphorous at eagle nest sites relative to control sites (~ 33% higher). Phosphorous is a limiting nutrient in coastal temperate forests, additions help to alleviate chlorosis and slow growth especially when paired with nitrogen. Higher potassium concentration also occurred on eagle-inhabited islands but was not associated specifically with current nest sites, perhaps reflecting differential persistence of macronutrients in the soil. I expected to observe elevated nitrogen isotope signatures (δ 15N) given bald eagles’ position in the trophic web and the potential for volatilization of guano but soil δ 15N abundance was not statistically higher at eagle nest sites. Total soil nitrogen was also not statistically higher at eagle nest sites. There were no significant differences between vegetation composition at eagle nest sites and reference sites, but reference sites tended to be dominated by shrub species / Graduate

We monitored distribution and abundance of food resources and determined food habits of nonbreeding bald eagles (<i>Haliaeetus leucocephalus</i>) on the northern Chesapeake Bay, as a preliminary step toward examining food-base effects on bald eagle distribution and abundance. To correctly interpret our food habits results, we first examined biases of 2 commonly-used food habits techniques, pellet analysis and food remains collection, through feeding trials with 2 captive bald eagles. Eagles were fed a variety of food items found on the northern Bay. Egested pellet contents and frequency of remains were compared with actual diet. We also examined efficacy of direct observation by observing eagles in high-use foraging areas. We found pellet analysis accurately indicated the species of birds and mammals eaten, but overrepresented medium-sized mammals and underrepresented large carrion in percent occurrence results. Fish were poorly represented in pellets. Eagles rarely produced pellets after eating fish, suggesting that pellet egestion rate, defined as the number of pellets produced per eagle per night, can serve as an index to relative use of birds and mammals. Food remains collection was highly biased toward birds, medium~sized mammals, and large, bony fish. Direct observation was labor intensive and required close proximity of the observer for unbiased identification of food items. Observation may be the only means of documenting eagles' use of small, soft-bodied fish. We used direct observation, pellet analysis, and pellet formation rates to determine bald eagle food habits from December 1986 through April 1988. We monitored fish abundance by gill netting and waterfowl abundance by aerial surveys over this same period. Fish and waterfowl abundance varied reciprocally; waterfowl numbers peaked in winter and fish numbers peaked in spring and late summer. Bald eagles responded to differences in food abundance with diet shifts. Canada geese (<i>Branta canadensis</i>), mallard (<i>Anas platyrhynchos</i>), and white-tailed deer (<i>Odocoileus virginianus</i>) carrion were primary foods from November through February. Cold-stressed gizzard shad (<i>Dorosoma cepedianum</i>) were captured frequently by eagles below a hydroelectric dam on the Susquehanna River in November and December, and also were taken frequently throughout the study area during a winter when ice cover was extensive. Shad were not commonly available during a milder winter. From April through September, bald eagles fed on a variety of fish species, primarily gizzard shad, channel catfish (<i>Ictalurus punctatus</i>), Atlantic menhaden (<i>Brevoortia tyrannus</i>), white perch (<i>Morone americana</i>), American eel (<i>Anguilla rosfrata</i>), and yellow perch (<i>Perca flavescens</i>). The 4 most commonly consumed fish species also were the most commonly gill netted species. At least 25% of all fish taken were scavenged. Live fish were most abundant at the water's surface in shallow water. Bald eagles' use of live fish reflected this availability; water depth at live fish capture sites was less than at sites where fish of dead or unknown status were taken. Eagles foraged most intensively within 1 hour of sunrise. A second smaller peak in foraging activity was observed in early afternoon. / Master of Science

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