Chapter 1: Population Genetics of Bald Eagles (Haliaeetus Leucocephalus) in Southern Idaho: Interactions of Life History with Reductions in Population Size
Historical and contemporary population bottlenecks and founder events reduce population size and shape the level and structure of genetic variability within and among populations. When populations have undergone consecutive demographic events, it may be difficult to disentangle the underlying forces that have influenced their genetic variation. I used molecular data and historical demographic information to infer the roles of demographic events and evolutionary forces on the level and structure of genetic variability within and among populations of Southern Idaho bald eagles. I collected DNA samples and analyzed six polymorphic microsatellite loci from seven breeding bald eagle populations in southern Idaho. Significant gametic phase disequilibrium (GPD) combined with heterozygote excess detected by the program BOTTLENECK indicated that bald eagles in southern Idaho have undergone historic and recent bottlenecks. Differences among levels of GPD, genetic variability and inbreeding among populations also indicated that the genetics of these populations have been impacted by various combinations demographic events (population bottlenecks and founder events) and evolutionary forces (genetic drift, gene flow, non-random mating). Long-established populations showed the highest levels of genetic variability and the most recently discovered populations showed the lowest levels. Estimates of FST, RST and AMOVA also revealed significant genetic differentiation among populations between regions. The current level and structure of genetic variability of Bald eagles in southern Idaho appears to have been shaped by both the number of reductions in population size and the relative recentness of reductions. The presence of population structure among regions suggests that juvenile dispersal is limited among regions and that contemporary levels of gene flow between populations has not been sufficient to overcome the consequences of small populations size. Conservation strategies for similar large, philopatric and slowly maturing raptors should focus on preventing population bottlenecks, as the life-history characteristics of these species appear to limit the rate of recovery of genetic variability.
Chapter 2: Characterization of Bald Eagle (Haliaeetus Leucocephalus) Population Growth in Long Valley, Idaho, From Small Population Size
The colonization of recently available habitat can result in founder events and small population size. Small founder populations undergo genetic drift (known as founder effects) which causes alterations and/or reductions in genetic diversity. When populations grow from small sizes, the rate by which genetic variability increases over time is determined by the rate of growth and the nature of recruitment into the populations: internal recruitment, immigration, or a combination of both. In instances where the parameters of population growth are difficult to measure using traditional means, changes in genetic variability over time can provide a reasonable means to infer the relative contributions of internal recruitment and immigration to population expansion from small size. The Long Valley bald eagle population in southern Idaho has grown from one known nest in 1976 to 17 in 2004. I used DNA from feather and blood samples collected in 1987, 2001, 2003, and 2004 to estimate genetic variability and relatedness among assumed unrelated individuals using 6 microsatellite loci. Gametic phase disequilibrium and inbreeding coefficients increased between 1987 and 2004 and indicated high levels of inbreeding apparently due to an increasing contribution of internal recruitment to population growth over time. Increases in allelic diversity between 1987 and 2004 were higher than expected from mutations and indicated that immigration has also contributed to growth in the Long Valley population. The presence of equilibrium conditions during 1987 and low inbreeding coefficients indicated a greater relative contribution of immigration to growth in the early history of this population. Increasing levels of gametic phase disequilibrium, Hardy-Weinberg equilibrium, and inbreeding coefficients indicated that inbreeding among individuals hatched into the population made relatively larger contributions to population growth than immigration after 1987. The Long Valley bald eagle population received limited gene flow and displayed inbreeding that appear to have limited it from thus far overcoming the genetic consequences of founder events. Continued genetic monitoring of this population will provide a better understanding of the balance between historical recruitment and immigration as expansion of the Long Valley population proceeds.
Chapter 3: Effects of Prey Availability and Fish Removal on Osprey Diet in West-Central Idaho
Prey capture in piscivorous birds is often significantly correlated with prey availability. Alterations of fish populations associated with human activities can have adverse impacts on the diets of breeding piscivorous birds. Non-game fish removal appears to impact the diets of piscivorous raptors by reducing the availability of preferred prey. I investigated the diets of ospreys nesting at Lake Cascade in west-central Idaho to document relationships between prey availability and osprey diet in relation to changes in fish abundance caused by non-game fish removal. I collected and identified prey remains from beneath and within 31 breeding osprey nests and characterized osprey diet during 2003 and 2004. Differences in Shannons index of diversity, raw biomass estimates by species between years were tested using mixed models and I also determined osprey prey preference by year using multivariate compositional analysis. I identified 178 and 344 individual prey items that represented 82 kg of dietary biomass from prey remains at 31 nests in 2003 and 2004, respectively. Fish accounted for 100% of the diet and benthic-feeding fish were most prominent in osprey diet during both years. Osprey diets however differed significantly between years due to differences in the relative contribution of largescale suckers, brown bullheads and northern pikeminnows to dietary biomass. Ospreys also utilized brown bullheads significantly more than all other species during both years. The diet of ospreys appears to be directly influenced by changes in fishery composition in response to fish removal practices at Lake Cascade.
Bechard, M.J., D.N. Perkins, G.S. Kaltenecker, and S. Alsup. 2009. Mercury contamination in Idaho Bald Eagles, Haliaeetus leucocephalus. Bulletin of Environmental Contamination and Toxicology 83:698-702.