Bald Eagle Nests Research Articles

Nesting Bald Eagle Population Numbers, Density, Territorial Resources, and Relationship to Human Development in Northern Colorado’s Front Range

To better understand the population of the Bald Eagle (Haliaeetus leucocephalus) nesting along northern Colorado’s Front Range, from 2016 to 2022 we studied 86 occupied nests within an area of 20,586 km2. From 2017 to 2020, 279 juveniles fledged from 237 nesting attempts in a smaller, main nest-study area with 68 nests. The nests’ success over these four years ranged from 52 to 70%, and their productivity varied from 1.1 to 1.3. The average nearest-nest distances for three discrete areas in the Front Range (5.03 to 7.26 km) are at least 2.8 to 4.0 times greater than these distances in four nesting populations in wetter regions but shorter than distances observed between nests in drier Arizona. In our study area the coverage of buildings within 400 m of Bald Eagle nests is relatively low by comparison to the coverage around randomly selected points, averaging 1344 m2; for 63% of the nests this coverage was less than 800 m2. We classified the 86 nest territories into eight categories that describe the dominant resource habitat and predicts the eagles’ reliance on Black-tailed Prairie Dogs (Cynomys ludovicianus) versus fish as prey. Predation on fish was predicted to be dominant at 51% (n = 44) of the nests, predation on prairie dogs at 32% (n = 28).

Nest Construction Costs Bald Eagles Time But not Breeding Success or Productivity

ABSTRACT Constructing nests costs birds time and energy and may influence breeding success and productivity. The precise nature and extent of these costs is understudied, particularly among raptor species. We used linear and generalized linear mixed models to examine the time and reproductive costs of nest construction to Bald Eagles (Haliaeetus leucocephalus) in New Jersey, USA, from 2009 to 2021. To differentiate nest construction costs from the influence of experience, we separately analyzed the breeding performance and phenology of new pairs constructing nests, established pairs constructing nests, and established pairs reusing nests. We also considered the influence of weather, year, and ecoregion. New territorial pairs building nests were generally less successful and productive than established pairs building or reusing nests. However, these trends were largely attributable to a greater egg-laying rate among established pairs. Nest building pairs, new and established, were generally delayed in egg laying, hatching, and nestling fledging compared to established pairs reusing nests; new pairs were notably more delayed than established pairs building nests. Territorial pairs in the Atlantic Coastal Pine Barrens were less successful and productive than pairs in other ecoregions. Higher precipitation around the egg laying period was predictive of lower nest success and productivity rates but did not appear to affect phenology. Higher temperatures around this period also lowered these rates, with the further effect of advancing phenology. In New Jersey, climate change appears to be advancing breeding phenology and could constrain productivity by century’s end, though we anticipate that density dependence will regulate and lower Bald Eagle breeding performance prior to this period. Breeding success and productivity rates, as well as the effects of year in our models, indicate that New Jersey’s breeding Bald Eagle population is still healthy and growing. Overall, our results indicate that nest construction imposes minor temporal costs on Bald Eagles but does not meaningfully affect their breeding success or productivity, which may help inform management of Bald Eagle nests and populations.

Predation of turtles by bald eagles (Haliaeetus leucocephalus) in the Southeastern United States

Understanding complete ecological roles of species requires insight into various predator-prey relationships. Bald eagles (Haliaeetus leucocephalus) have been documented to consume a variety of species, including turtles. The ground beneath eight bald eagle nests located in Alabama and Tennessee were searched during the 2016, 2017, and 2018 nesting seasons for discarded turtle remains. Six turtle genera were documented, but the most abundant turtle genera observed were Graptemys and Sternotherus. Most remains were juveniles or adult males; however, the Sternotherus remains could have been adult males or females. The distance of the eagle nest to the nearest major waterway appeared to influence whether Graptemys or Sternotherus was the major turtle prey observed. The presence of different contaminants in these turtle species should be examined to determine if they potentially contribute to biomagnification in bald eagles.

Changes in Bald Eagle Nesting Distribution and Nest-Site Selection in Kentucky during 1986–2019

Kentucky's breeding Haliaeetus leucocephalus (Bald Eagle) population began recovering in 1986, with a single nest, and has since expanded from the state's western portion to the central and eastern regions. We used aerial survey data to describe the spatiotemporal distribution of Bald Eagle nests in Kentucky, to examine changes in nest-site selection relative to natural and anthropogenic features, and to create a nesting-habitat suitability model. Our results highlight increased nesting near developed areas in recent years. Although nests in these areas productively contribute to populations, we note some considerations of increased risks associated with nesting in developed areas. We also provide predictions of available nesting areas and data to direct the future monitoring and management of Bald Eagles in Kentucky.

Modeling current and future habitat suitability of an iconic bird to inform restoration planning in southeastern Louisiana, U.S.A.

Louisiana is facing a land loss crisis with 5,000 km2 lost since the 1930s, and another 10,000 km2 may disappear over the next 50 years. In response, the state developed a Comprehensive Master Plan for a Sustainable Coast, which includes predictions for how wildlife species respond to futures with or without restoration action. However, the 2017 Master Plan did not include a bird species representative of brackish or freshwater wetland habitats. Our objective therefore was to evaluate the potential for the Bald Eagle (Haliaeetus leucocephalus) to serve as an indicator of freshwater wetland health, and to develop a model to predict Bald Eagle responses to land cover change 20 and 50 years into the future, with or without restoration action. Using nest location data collected by the Louisiana Department of Wildlife and Fisheries from the Barataria Basin, we modeled the relationship between Bald Eagle nest occurrence and land cover using boosted regression trees. Model performance was strong, explaining 54.4 ± 0.1% of the deviance in nest occurrence, and showed that Bald Eagle nests were more common in areas with greater fresh forested wetland, freshwater marsh, and flotant marsh land cover. Future suitability for nesting Bald Eagles was higher in 20 and 50 years with restoration action compared to without, although suitability in both years was lower than contemporary suitability, regardless of restoration action. Our model suggests that comprehensive restoration action is needed, including the implementation of Mississippi River diversions, to sustain high densities of nesting Bald Eagles in coastal Louisiana.

Bald eagle mortality and nest failure due to clade 2.3.4.4 highly pathogenic H5N1 influenza a virus

The bald eagle (Haliaeetus leucocephalus) is a culturally and ecologically vital species in North America that embodies conservation success but continues to face threats that include emerging pathogens. The introduction of A/goose/Guangdong/1/1996 lineage highly pathogenic (HP) clade 2.3.4.4b H5N1 influenza A virus (IAV) in North America in late 2021 resulted in high rates of mortality among bald eagles. Here we show an alarming rate of bald eagle nest failure and mortality attributed to HP IAV. We documented fatal, systemic HP IAV infection in breeding adult and nestling bald eagles along the southeastern U.S. coast. Concurrently, annual bald eagle nest surveys in Georgia and Florida revealed a precipitous drop in success in coastal counties compared with previous years, portending negative impacts on population recruitment. As an apex predator and efficient scavenger, it is likely that bald eagles become infected through consumption of infected waterfowl. These results and similar reports of raptor mortality in Europe, Asia, and Africa, indicate a clear threat to raptor health. The possible long-term persistence of HP H5N1 IAV in North America poses an impending threat to bald eagle populations not only related to direct mortality but also decreased recruitment and warrants continued efforts to understand these potential impacts.

Home Range of a Breeding Male Bald Eagle (Haliaeetus leucocephalus) Tracked via Satellite Telemetry in Kentucky

Haliaeetus leucocephalus (Bald Eagle) is a well-studied species, and information on their nest abundance and population trends is widely available. However, research on the movements and home range of nesting Bald Eagles in the interior US is lacking. In this study, we used a solar-powered Argos platform transmitter terminal (PTT) with global positioning system (GPS) capabilities to monitor the movements of an adult, breeding male Bald Eagle, captured at Ballard Wildlife Management Area, KY, from 29 April 2012 to 23 October 2013. We generated minimum convex polygons (MCP) for comparisons to previous studies and used 95% and 50% fixed kernel density estimators (KDE) to estimate home-range size and core-use areas, respectively, during nesting and non-nesting periods. Estimates of home range and core-use areas were slightly larger during the non-nesting period (MCP = 420.0 km2, 95% KDE = 1.6 km2, 50% KDE = 0.2 km2) when compared to the nesting period (nesting MCP=415.0 km2, 95% KDE =1.3 km2, 50% KDE = 0.01 km2). Our home range and core-use estimates were smaller than previous studies using comparable methods, suggesting that habitat quality at this site may be high.

Influence of nesting Bald Eagles (Haliaeetus leucocephalus) on Common Loon (Gavia immer) occupancy and productivity in New Hampshire

ABSTRACT Bald Eagles (Haliaeetus leucocephalus) and Common Loons (Gavia immer) have been the subject of intensive recovery efforts over 4 decades in New Hampshire. In the last 2 decades, eagles hav...

Managing individual nests promotes population recovery of a top predator

Abstract Threatened species are managed using diverse conservation tactics implemented at multiple scales ranging from protecting individuals, to populations, to entire species. Individual protection strives to promote recovery at the population‐ or species‐level, although this is seldom evaluated. After decades of widespread declines, bald eagles, Haliaeetus leucocephalus, are recovering throughout their range due to legal protection and pesticide bans. However, like other raptors, their recovery remains threatened by human activities. Bald eagle nests are commonly managed using buffer zones to minimize human disturbance, but the benefits of this practice remain unquantified. Within Voyageurs National Park (VNP), Minnesota, USA, managers have monitored bald eagle populations for over 40 years, and since 1991, have protected at‐risk nests from human disturbance using buffer zones (200 and 400 m radius). We aimed to (1) quantify the recovery of bald eagles in VNP (1973–2016), and (2) provide a first‐ever evaluation of the individual‐ and population‐level effects of managing individual nests. To do so, we developed Bayesian Integrated Population Models combining observations of nest occupancy and reproductive output (metrics commonly collected for raptors) to estimate nest‐level probabilities of occupancy, nest success, and high productivity (producing ≥2 nestlings), as well as population‐level estimates of abundance and growth. The breeding population of bald eagles at VNP increased steadily from <10 pairs in the late 1970s to 48 pairs by 2016. At the nest‐level, management significantly improved occupancy and success. At the population‐level, management led to 8% and 13% increases in nest success and productivity rates, respectively, resulting in a 37% increase in breeding pair abundance. Synthesis and applications. There is a clear need to evaluate how management approaches at multiple scales assist in species recovery. Our study uses an Integrated Population Model to reveal the population‐level benefits of a widely used, individual‐based management action (protecting nests using buffer zones) on a recovering raptor.

Shifts in Great Blue Heron Habitat use Following Nest Site Usurpation: Implications for Salmonids

Abstract Interactions among predators can have important consequences for lower trophic levels. Here, we use individual tag data on juvenile salmonids to quantify how their geographic, taxonomic, and life-history representation in the diets of great blue herons (Ardea herodias) changed after a pair of bald eagles (Haliaeetus leucocephalus) usurped the colony's nesting site, forcing the colony to relocate. Heron diet composition changed significantly despite the short relocation distance (4.1 km). This was driven by a shift in space use, as herons to a greater extent began consuming fish from a river basin farther away from the bald eagle nest. As a consequence the species composition in heron diets changed significantly, with the largest increase in coho (Oncorhynchus kisutch) and largest decrease in Chinook salmon (O. tshawytscha). The representation of Chinook life-history types in the diets also shifted. Fall Chinook was the numerically dominant life-history type in the diets but decreased relative to ...

Improving bald eagle nest monitoring with a second spring survey

Failure to account for observation error can cause bias in estimators of variables important for wildlife management and conservation, such as abundance, occupancy, and species composition. Therefore, long-term monitoring programs need to evaluate sources of bias to ensure that objectives of the program can be met. Although trend estimation is possible using biased estimators, population status, and management decisions can be sensitive to random and systematic heterogeneity in the observation process. For example, standard methods used to monitor reproductive attempts at bald eagle (Haliaeetus leucocephalus) nests fail to quantify observation error. We used bald eagle nest surveys from 3 national parks in Alaska, USA, to examine their ability to accurately estimate nesting attempts and hypothesized that our ability to perfectly observe nesting activity was related to the timing of the survey relative to peak nest attendance by eagles. We therefore, developed 3 scenarios that evaluated our ability to correctly identify nesting status metrics: peak nesting remained unchanged (observed variation scenario), reduced ability to predict peak nest attendance (high heterogeneity scenario), and peak nest attendance occurred earlier than the survey window (low detection scenario). Eagle nest attendance was consistently underestimated using naive estimators, but productivity (predicted no. chicks/nesting attempt) was not affected by imperfect detection. All scenarios showed that using replicate observations to model imperfect detection corrected estimator bias for nest attendance and improved the estimator precision for both metrics. Our study demonstrates that imperfect observation of bald eagle nesting activity using standard methods results in estimator bias and reduced precision if not corrected. Further, our simulations show that changes in observation conditions can affect estimator bias and precision, which is an important consideration for long-term monitoring programs. Therefore, formally modeling imperfect detection should be completed for monitoring programs designed to use nesting status to inform management or conservation decisions. © 2017 The Wildlife Society.

The Bald Eagle Nests: The United States Role in State-Building: Germany, Kosovo, and Iraq

The Bald Eagle Nests: The United States Role in State-Building: Germany, Kosovo, and Iraq

Foraging ecology of a reintroduced population of breeding Bald Eagles on the Channel Islands, California, USA, inferred from prey remains and stable isotope analysis

Successful management of reintroduced populations requires recognizing that ecological conditions may have changed between extirpation and reintroduction. For example, characterizing dietary patterns of generalist apex predators in the past and present can help to define how their functional role may change as translocated populations grow. We identified prey remains collected from Bald Eagle (Haliaeetus leucocephalus) nests and used carbon (d 13 C) and nitrogen (d 15 N) stable isotope analysis to quantify diet composition of the recently reintroduced Bald Eagle population on the Channel Islands off southern California, USA. We collected .6,000 prey items from recently occupied nests on Santa Catalina, Santa Rosa, Santa Cruz, and Anacapa islands in 2010 and 2011. Prey identification and stable isotope analysis yielded similar results and showed that eagles on Santa Catalina Island consumed a high proportion (~60%) of marine fish and a lower proportion (25–30%) of seabirds, while their counterparts on the Northern Channel Islands consumed equal proportions (~40–45%) of these prey types. Terrestrial resource use was low with the exception of eagles from one nest on Santa Catalina Island, where eagles primarily consumed ground squirrels and freshwater fish. We suggest that a combination of natural and anthropogenic factors is responsible for the interisland differences in Bald Eagle diet. Bald Eagle interactions with a robust recreational fishery off Santa Catalina Island may enhance access to fish species that are not available to eagles on the Northern Channel Islands, where the availability of breeding seabirds is far greater. The proportion of seabirds consumed by eagles on the Northern Channel Islands today is similar to that consumed by eagles from this region historically and prehistorically. This suggests that the restoration of breeding seabirds on the Channel Islands will benefit the long-term viability of eagle populations in the northern archipelago.

Estimating the residual value of alternate bald eagle nests: Implications for nest protection standards

For over 30 years, bald eagle (Haliaeetus leucocephalus) nests and nest trees have been managed using a combination of spatial buffers and time-of-year restrictions. Most management standards include the protection of nests currently in use as well as alternate nests and trees that have lost nests. Protection is extended to alternate nest structures under the assumption that they provide value to the breeding population. However, the notion that these structures hold enough residual value to warrant the cost of their protection has not been fully explored. I used nest histories (n > 2,250) from a long-term (1962–2011) dataset collected in the lower Chesapeake Bay to evaluate the relationship between management costs and residual value across the range of management scenarios currently in use. I used a joint, multistrata, live-recapture/dead-recovery model in Program MARK to estimate probabilities of annual survival for active and alternate nests and transition probabilities between active and alternate nests. My primary objective was to assess the residual biological value of alternate nests and trees relative to the management costs required to protect them. I estimated the per capita management costs and the residual value of alternate nests and trees. Survival rates were 0.902 ± 0.007 (mean ± SE) and 0.703 ± 0.017 for active and alternate nests, respectively. Of 1,163 alternate nests, 352 (30.3%) were determined to be re-used within 5 years. However, the likelihood of re-use declined with time. Most re-used nests were re-used in the first year (76.4%), with virtually all (98.6%) being re-used in the first 3 years. Only 9.9% (168 of 1,699) of trees that had lost nests were re-used within the first 10 years. Nests were rebuilt in 32% (equating to 3.1% re-use) of re-used trees in the first year and in 71.4% of these trees in the first 3 years. Implementation of current national management guidelines resulted in 2.35 nest equivalents of management cost for each active nest in the population. The residual value and cost functions diverged over time such that the return on social investment diminishes over the management periods. The cost-to-benefit relationship is particularly poor when the protection of alternate nests is extended beyond 3 years and when protection is extended to trees that have lost nests. © 2015 The Wildlife Society.

Nest Guarding in Chesapeake Bay Bald Eagles

Abstract As Bald Eagle (Haliaeetus leucocephalus) populations approach carrying capacity in the Chesapeake Bay, competition for breeding territories appears to be intensifying. Frequent territorial interactions may force breeders to adjust nest-guarding behavior. We examined nest-guarding behaviors at active Bald Eagle nests in the lower Chesapeake Bay during the nesting season (2012 and 2013). Guarding coverage was 13.7 ± 4.2% of total observation time during the pre-laying period, 6.8 ± 2.2% of observation time in the incubation period, and 26.3 ± 3.2% of observation time in the nestling period. Females were present in the nest area for 80.0 ± 2.7% of the nestling period. Although males were present only 51.2 ± 2.8% of the nestling period, male breeders guarded nests twice as often as females. Adults guarded most often from perches in adjacent trees and within 25 m of the nest. If increasing rates of conspecific interactions force males to allocate more time to nest guarding, a tradeoff may occur, with ...

Intraspecific Intrusion at Bald Eagle Nests

Competition for nesting territory has been shown to act as a density-dependent feedback mechanism influencing population growth rate. However, little is known about the nature of territorial interactions between established breeders and floaters. We examined territorial intrusion rates and associated behaviours at active Bald Eagle Haliaeetus leucocephalus nests in the lower Chesapeake Bay in 2012 and 2013. The average intrusion rate experienced at study nests during the reproductive period was 0.28 ± 0.32 intrusions/h. Variance in intrusion rate was high and there was no apparent predictive pattern to these events. Juvenile intrusions occurred closer to the nest than adult intrusions, and breeders showed higher response rates toward adults, with 78% of adult intruders eliciting a response compared to 47% of juveniles. Breeding adults responded to intruders significantly more often and more aggressively when in the presence of their mate. Further research is necessary to broadly describe the relationship ...

Using double-observer aerial surveys to monitor nesting bald eagles in Alaska: Are all nests available for detection?

The abundance of nesting eagles is often identified as the parameter of primary interest for monitoring their populations. We compared the standard dual-frame estimator, which is recommended in the bald eagle post-delisting monitoring plan, with a Bayesian multistate capture-recapture approach to estimate the total number and number of active nests (nests with incubating adults) along the remote Kenai Fjords National Park coastline from 2009 to 2012. Two independent observers conducted aerial surveys of random transects during peak nest initiation in May. Both methods produced similar estimates of nest abundance, but the Bayesian multistate model allowed more flexibility to accommodate shifting management priorities. Estimates of the total number of nests and the number of active nests increased by approximately 49% between 2009 and 2012. This increase was much greater than expected based on feasible rates of nest loss and creation for our study area, indicating apparent estimator bias. Survey-specific conditions (e.g., aircraft height) that made some nests unavailable to both observers were the most likely cause of the bias. We recommend that bald eagle nest monitoring include 2 surveys during the early breeding season to reduce bias of annual capture-recapture estimators. Our results demonstrate that incomplete availability may be an important source of bias for many double-observer aerial wildlife surveys. Published 2014. This article is a U.S. Government work and is in the public domain in the USA.

Bald Eagle Nesting Habitats in the Upper Mississippi River National Wildlife and Fish Refuge

Bald Eagle Nesting Habitats in the Upper Mississippi River National Wildlife and Fish Refuge

Bald Eagle Nesting Habitats in the Upper Mississippi River National Wildlife and Fish Refuge

AbstractThis study examined habitat variables associated with 53 active bald eagle Haliaeetus leucocephalus nest sites in the Winona District of the Upper Mississippi River National Wildlife and Fish Refuge, Minnesota and Wisconsin. The Refuge is the most heavily visited refuge in the United States, where breeding eagle populations have been increasing dramatically. During February–April 2009, nest trees were identified and measured, nest heights were determined, distances to nearest water bodies were assessed, and forest inventories were conducted for the standing timber surrounding the nest trees. Nest densities and spacing were assessed within each navigation pool, and land cover types were examined within 100- and 1,000-m radii around known eagle nest sites and random points within the Refuge. Ninety-three percent of nest sites had supercanopy eastern cottonwoods Populus deltoides and silver maples Acer saccharinum as the nest trees. Potential human disturbances from highways, railroads, and commercial barge and recreational boat traffic were present within 400 m of 90% of known nest sites. Eagle nest sites were located an average of 1.52 km from the next nearest nest, with nest densities ranging from 0.32 to 9.72 nests/100 km2 among the four navigation pools of the Winona District. Land cover types around known nest sites and random points differed significantly at both 100- and 1,000 m scales, with wet forest and open water significantly more abundant and agricultural and developed lands significantly less abundant than around randomly selected points. Successful nests that fledged at least one young were spaced significantly further away from other active nests and were located in areas with lower tree density than were unsuccessful nests. Floodplain-nesting bald eagles tended to select the tallest, dominant trees for nest sites, placing nests near the height of the surrounding canopy. Human presence within the Refuge does not appear to be limiting the expansion of nesting bald eagles in this riverine habitat.

First Record of Nesting Bald Eagles at Last Mountain Lake National Wildlife Area

First Record of Nesting Bald Eagles at Last Mountain Lake National Wildlife Area