Anthropogenic pressures on the global landscape are rapidly increasing, with well-documented negative impacts on avian populations. As an encouraging counterexample to general declines, the bald eagle Haliaeetus leucocephalus population in the United States has continued to grow dramatically since its 20th century decline, with breeding pairs now colonizing areas with high levels of human activity. Evidence of the impact of human activity on nesting bald eagles is mixed, with some studies reporting declines in reproduction, whereas others suggest that reproduction is comparatively unaffected. We assessed the effects of anthropogenic activities on bald eagle nest success by compiling data from incidental take permits issued by the U.S. Fish and Wildlife Service for unintentional disturbance of breeding bald eagles. We used generalized linear logistic regression models in a Bayesian framework to evaluate the relationship between types of human activity (n = 6), levels of human development in the environment around nests (n = 5), and whether the activity resulted in a significant alteration of the surrounding habitat. There were more permits issued for nests in suburban (40%) environments than in natural (12%) or industrial (9%) environments, and nearly half (47%) of the permits were for building activities; there was a similar number of permits where the habitat was altered (46%) or unaltered (54%). Overall mean nest success during authorized activities from 103 nest-seasons was 84% (95% credible interval: 76–90%), and nest success rates were similarly high (77–100%) for all categories within covariates (P > 0.6). The top model was without fixed effects, accounting for 47% of the model set weight, and the next three models, the only other models with widely applicable information criterion weight, included the activity type and habitat alteration covariates. The only parameters with 95% credible intervals that did not encompass 0 were infrastructure and landscape modification activities, for which all nests exposed to these activities were successful; however, these estimates also had very high uncertainty. This indicates that the covariates we tested were weak predictors of nest success. Some permitted nests were monitored before or after years of authorized activity, and there was no significant difference in nest success between activity and nonactivity years. We provide further evidence that the growing contingent of bald eagles nesting in human-developed environments tolerate anthropogenic activities to a degree that they can nest successfully at rates comparable to those of the general U.S. population. This study improves our understanding of bald eagle reproductive performance when exposed to human activities and will provide better guidance for managing this species.

Three-quarters of the global land surface is experiencing measurable human pressures (Venter et al. 2016), and these pressures can have significant negative impacts on wildlife populations (Hill et al. 2017; Gaynor et al. 2018; Katzner et al. 2020). Bird populations are particularly vulnerable to a wide range of anthropogenic stressors, with annual estimates of human-caused avian mortalities in the United States numbering in the billions (Loss et al. 2015). Anthropogenic activities can directly or indirectly affect avian survival and reproduction. Direct effects can emanate from anthropogenic sources, such as collisions with manmade structures (e.g., buildings, communication towers, wind turbines, and electrical infrastructure) or vehicles (e.g., automobiles and aircraft), poisoning, electrocution, illegal shooting, pollution, agricultural practices, predation by domestic cats, and invasive pathogens (Loss et al. 2012). Additionally, nonlethal anthropogenic stressors, such as habitat loss or degradation, climate change, and sensory disturbance, can indirectly impact bird populations by altering foraging, sheltering, or breeding behavior, which can compromise individual fitness and result in reduced productivity or nest abandonment, causing reproductive failure (Katzner et al. 2020).

Populations of bald eagles Haliaeetus leucocephalus, a large raptor that ranges from northern Mexico to much of the United States and Canada, have experienced two periods of severe decline from anthropogenic sources (Gerrard and Bortolotti 1988). The first was from human persecution during the first half of the 20th century, and the second occurred in the mid-20th century, a result of widespread use of organochlorine pesticides (in particular, dichloro-diphenyl-trichloroethane [DDT]), which caused significant reductions in productivity or reproductive failure (Grier 1982; Buehler 2000; Dykstra et al. 2001). Following enactment of the Bald and Golden Eagle Protection Act of 1940 (16 U.S.C. 668-668d, as amended), the bald eagle being listed in 1967 under the Endangered Species Preservation Act and precursors (Pub. L. 89-669; 16 U.S.C. 1531), and a ban on DDT in 1972 across the United States (37 FR 13369; USEPA 1972), bald eagle populations recovered sufficiently for the species to be delisted by 2007 (72 FR 37346; USFWS 2007a). In 2009, the U.S. Fish and Wildlife Service (USFWS) promulgated regulations to authorize permitted take for bald eagle nest disturbance, where the take is incidental, but not for the purpose of otherwise lawful activities (74 FR 46836; USFWS 2009). The USFWS revised the regulations in 2016 to improve the permitting framework and update eagle management objectives, allowing for take that is consistent with the goals of maintaining a stable or increasing breeding population (81 FR 91494; USFWS 2016a). Bald eagle populations in the United States continued to grow after delisting and demonstrated an estimated fourfold increase from 2009 to 2018 (Zimmerman et al. 2022). This trend included an expansion of breeding populations into developed environments (Castle et al. 2023).

Past research indicated that bald eagles can be sensitive to human proximity and disturbance (Fraser and Anthony 2008). Many studies have examined the behavioral response of breeding bald eagles to human sensory disturbance (Grubb and King 1991; Steidl and Anthony 2000; Watson 2004) or nest-site selection when exposed to anthropogenic stressors (Andrew and Mosher 1982; Saalfeld and Conway 2010; Mundahl et al. 2013). Findings from studies like these are useful for developing management recommendations regarding breeding pairs or individual nests. Indeed, the USFWS guidelines for conducting activities near bald eagle nests include recommendations for buffer distances between the nest and these activities based on the type of activity and whether it is visible from the nest (USFWS 2007b). This type of research, however, does not further our understanding of the impact of nest disturbance at a population level; this requires assessing the demographic response to these anthropogenic activities. Several studies have demonstrated human activity negatively impacting bald eagle nest success or productivity (Bangs et al. 1982; Anthony and Isaacs 1989; Steidl 1994). However, there is a growing body of evidence suggesting that breeding bald eagle populations may be much more resilient to human disturbance than previously thought (Figure 1). Some studies found that anthropogenic activities were not adversely affecting reproductive rates (Fraser et al. 1985; Anthony et al. 1994; Millsap et al. 2004; Goulet et al. 2021). Clearly, the response of breeding bald eagles to human disturbance is highly variable and may depend on the type of anthropogenic activity (e.g., recreation, construction, and resource extraction) or the environment in which nests are located.

Figure 1.

Bald eagle Haliaeetus leucocephalus nests in close proximity to anthropogenic activities. The photo on the left (taken in 2017) shows a nest during construction of Mariner’s Pointe, a multiple-dwelling, residential housing development in Hopatcong, New Jersey; this nest is in our data, and it was successful in both years that it was monitored during the authorized activity. The photo on the right (taken in 2014) shows a nest near the Tilcon Mount Hope Quarry in Rockaway, New Jersey; this nest has been in continuous use for more than 11 years, and breeding pairs were productive for many of those years despite anthropogenic activities occurring within 60 m of the nest (D. Brill, EcoSciences Inc., personal communication). Images used with permission from photographer D. Brill, EcoSciences Inc.

Figure 1.

Bald eagle Haliaeetus leucocephalus nests in close proximity to anthropogenic activities. The photo on the left (taken in 2017) shows a nest during construction of Mariner’s Pointe, a multiple-dwelling, residential housing development in Hopatcong, New Jersey; this nest is in our data, and it was successful in both years that it was monitored during the authorized activity. The photo on the right (taken in 2014) shows a nest near the Tilcon Mount Hope Quarry in Rockaway, New Jersey; this nest has been in continuous use for more than 11 years, and breeding pairs were productive for many of those years despite anthropogenic activities occurring within 60 m of the nest (D. Brill, EcoSciences Inc., personal communication). Images used with permission from photographer D. Brill, EcoSciences Inc.

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Our objective was to evaluate nest success (i.e., fledging ≥ 1 young) of bald eagles in areas with different levels of human development throughout the United States when exposed to anthropogenic activities. We hypothesized that bald eagles have developed some tolerance to human-dominated landscapes in terms of reproductive success. In our study, we predicted that nest success of bald eagles exposed to human activity under permit would be similar to success under normal environmental conditions. Improving our understanding of bald eagle reproductive performance when exposed to human activities will provide better guidance for managing this species.

In 2007, the USFWS published the National Bald Eagle Management Guidelines (NBEMG) following delisting of the bald eagle and in anticipation of publication of nest disturbance permitting regulations (USFWS 2007b). The NBEMG recommend various combinations of distance buffers, breeding season timing restrictions, and visual barriers according to the type of anthropogenic activity. These recommendations were based on expert opinion and the best available science at the time, and the assumption was that activities not conforming to NBEMG would result in nest failure due to disturbance and therefore would require a disturbance permit. We aimed to assess and potentially update these recommendations based on our analyses of success rates of bald eagle nests identified under USFWS permits authorizing activities that may cause nest disturbance. Therefore, we compiled data from bald eagle nest disturbance permits issued by the USFWS from 2009 to 2021 that authorized activities that did not adhere to NBEMG.

We examined the effects of anthropogenic activities on bald eagle nest success and therefore only included data from permits under the following circumstances: 1) nests were occupied (i.e., nest contains eggs, young, or an incubating bird, has a pair of birds on or near it, or has been recently repaired or decorated [Steenhof et al. 2017]) during any phase of nesting behavior within the period(s) of the permitted activity for which sufficient monitoring and reporting was conducted to reliably determine nest success; 2) permits were not combined with any other authorization, and authorized activity was for one nesting pair only (i.e., this could mean one nest or several nests presumed to be in the same territory); and 3) permits were not amended once the first period of permitted activity commenced. Moreover, we only considered bald eagle nests that could be “disturbed” according to the following regulatory definition (50 C.F.R. Section 22.6) for disturbance created by the USFWS:

…to agitate or bother a bald or golden eagle to a degree that causes, or is likely to cause, based on the best scientific information available, (1) injury to an eagle, (2) a decrease in its productivity, by substantially interfering with normal breeding, feeding, or sheltering behavior, or (3) nest abandonment, by substantially interfering with normal breeding, feeding, or sheltering behavior.

Thus, our analyses excluded intentional or unintentional removal or destruction of bald eagle nests or nest trees.

We compiled data on the geographic location of bald eagle nests, including latitude, longitude, and state. We used two additional variables from the permits to inform whether the authorized activity adhered to NBEMG and, if so, whether we should include it in the data. These variables were minimum distance (m) between the nest and the edge of the activity area (buffer) and degree of visibility of the activity from the nest (visible, partially visible, or not visible). For example, NBEMG recommend a buffer of 100 m if the activity is not visible from the nest and 200 m if it is visible, and this depends on the type of activity (see NBEMG [USFWS 2007b] pages 11–14). For our purposes, when determining inclusion of data in our analyses, we treated “partially visible” the same as “visible.” When available, we also recorded data on nest success for up to three nesting seasons before and after the years when the authorized activity occurred.

We ran generalized linear logistic regression models in R 3.6.2 (R Core Team 2019) in a Bayesian framework using NIMBLE 0.12.1 (de Valpine et al. 2017) to assess the relationship between characteristics of anthropogenic activity and bald eagle nest success. The binary response variable was nest success or failure, and we considered a nest successful if the breeding pair fledged at least one young. The covariates that we tested in our models included primary environment (the predominant level of human development within a 1.6-km radius of the nest), primary activity (the predominant activity authorized in the permit), and habitat alteration (the authorized activity resulted in significant alterations of the surrounding habitat: 0 = no and 1 = yes; see Table 1 and Table S1, Supplemental Material, for covariate details). We used the following global model:
formula
formula
where, for the i th nest-season (i.e., a nesting season during the authorized activity in which nest outcome was determined), >yi was nest success (0 = fail and 1 = success), was the probability of nest success, β0 was the intercept, βEnv was the primary environment coefficient, env[i] was the primary environment category (suburban [reference], urban, rural, natural, or industrial), βAct was the primary activity coefficient, act[i] was the primary activity category (building [reference], recreational, infrastructure, resource [extraction, operations, or maintenance], transportation [and service], or landscape modification), βAltHab was the habitat alteration coefficient, and althab[i] was the habitat alteration category (0 = no and 1 = yes). We initially tested models that included a random effect for nest, but these models performed poorly at estimating some parameters. We feel that this was likely the result of a combination of an overall small sample size, low variation in nest success (i.e., a very high proportion of nests were successful), and a low number of nests that were monitored for multiple years (very few nests were monitored for more than 2 years). Therefore, we did not include a random effect for nest in the models. We feel that the covariates included in the models serve as a good assessment of variability in territory quality by describing the level of human development, types of sensory disturbance, and habitat modifications surrounding nests. In addition, for permitted nests that were monitored before or after years of authorized activity, we ran intercept-only models using those data to compare nest success before and after the activity occurred with nest success during the authorized activity.
Table 1.

Summary of the data that we used in analyses from bald eagle Haliaeetus leucocephalus nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 (n = 68). Nest-seasons = nesting seasons during authorized activity in which nest outcome was determined (n = 103).

Summary of the data that we used in analyses from bald eagle Haliaeetus leucocephalus nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 (n = 68). Nest-seasons = nesting seasons during authorized activity in which nest outcome was determined (n = 103).
Summary of the data that we used in analyses from bald eagle Haliaeetus leucocephalus nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 (n = 68). Nest-seasons = nesting seasons during authorized activity in which nest outcome was determined (n = 103).

We modeled nest success as a linear function on the logit scale and assigned vague N(μ = 0, τ = 0.0001) priors to model parameters. We ran models for 100,000 iterations and discarded the initial 20,000 samples as burn-in. We ranked competing models by their widely applicable information criterion (WAIC; Watanabe 2010) values and WAIC weights (WAICω). We tested for correlations among model covariates using a bias-corrected Cramér’s V test, whereby a V value of <0.4 indicates weak correlation (Cramér 1946). We further tested for multicollinearity among covariates in the multivariate models with variance inflation factors (Neter et al. 1996). We ran χ2 goodness-of-fit tests on the model covariates to test for significant differences from expected frequencies among categories within each covariate (data collated by permit) and for nest success among categories within covariates (data collated by nest-season). We assessed the certainty of parameter effects being in the same direction as the mean (i.e., the probability of a negative or positive effect for a given parameter) by calculating P values derived from the probability of direction (pd) with the bayestestR package (Makowski et al. 2019). We used R 3.6.2 (R Core Team 2019) for all statistical analyses, and we accepted probabilities of α < 0.05 as significant.

Regional USFWS staff submitted data from 273 bald eagle nest disturbance permits issued by the USFWS from 2009 to 2021, of which 68 permits met our criteria for inclusion in analyses for a total of 103 nest-seasons. Data included bald eagle nests in 18 states in the contiguous United States distributed primarily across the north-central Midwest, northeast, southeast, and Pacific northwest regions (Figure 2). Gaps in the geographic distribution of the nests are due to spatial variation in frequency of anthropogenic activities coinciding with bald eagle nests, willingness of project proponents to apply for permits, variability among USFWS regions in conditions imposed on permits, regional-scale abundance of breeding bald eagles, and regional staff access to historic permit and annual report documents.

Figure 2.

Map of bald eagle Haliaeetus leucocephalus nests (red dots) that we included in analyses where anthropogenic activities were authorized during the nesting season under permits issued by the U.S. Fish and Wildlife Service from 2009 to 2021. Note that although we included 68 permits in our data, only 66 nests are shown; 1 permit did not include the geographic location of the nest, and 1 nest was covered by 2 permits.

Figure 2.

Map of bald eagle Haliaeetus leucocephalus nests (red dots) that we included in analyses where anthropogenic activities were authorized during the nesting season under permits issued by the U.S. Fish and Wildlife Service from 2009 to 2021. Note that although we included 68 permits in our data, only 66 nests are shown; 1 permit did not include the geographic location of the nest, and 1 nest was covered by 2 permits.

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There were more permits issued for nests in suburban environments (40%) and fewer for nests in natural (12%) or industrial (9%) environments (χ2 = 21.6, df = 4, P < 0.001; Table 1). The activities authorized under these permits were more often for building (47%) and less often for recreation, infrastructure, landscape modification, or resource extraction, operations, or maintenance (9% each; χ2 = 47.8, df = 5, P < 0.001; Table 1). There was no significant difference in the number of permits issued where the habitat was altered (46%) or unaltered (54%; χ2 = 0.53, df = 1, P = 0.467; Table 1).

The overall mean (95% credible interval [CrI]) nest success during authorized activities was 84% (76–90%; n = 103 nest-seasons), and this did not vary significantly among categories for primary environment (range: 77–92%; χ2 = 1.216, df = 4, P = 0.876), primary activity (range: 78–100%; χ2 = 3.650, df = 5, P = 0.601), or habitat alteration (range: 82–85%; χ2 = 0.017, df = 1, P = 0.895; Table 1). Of the nests monitored in years before activity (n = 23 nest-seasons), 75% (52–90%) were successful, and in those same nests during activity, 75% (55–89%; n = 19 nest-seasons) were successful (Table 2). Of the nests monitored in years after activity (n = 19 nest-seasons), 94% (79–99%) were successful, and in those same nests during activity, 92% (73–99%; n = 25 nest-seasons) were successful (Table 2). There were four nests that were monitored both in years before and after activity, and for only those nests, success before activity was 70% (28–95%; n = 6 nest-seasons), success during activity was 89% (48–100%; n = 6 nest-seasons), and success after activity was 93% (63–100%; n = 9 nest-seasons; Table 2).

Table 2.

Estimates of mean bald eagle Haliaeetus leucocephalus nest success, standard deviation, and 95% credible intervals for nests listed in bald eagle nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 that were monitored in years before (Prepermit) and after (Postpermit) years of authorized activity (Permit Years). We estimated percentages across rows from the same permits.

Estimates of mean bald eagle Haliaeetus leucocephalus nest success, standard deviation, and 95% credible intervals for nests listed in bald eagle nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 that were monitored in years before (Prepermit) and after (Postpermit) years of authorized activity (Permit Years). We estimated percentages across rows from the same permits.
Estimates of mean bald eagle Haliaeetus leucocephalus nest success, standard deviation, and 95% credible intervals for nests listed in bald eagle nest disturbance permits issued by the U.S. Fish and Wildlife Service in the United States from 2009 to 2021 that were monitored in years before (Prepermit) and after (Postpermit) years of authorized activity (Permit Years). We estimated percentages across rows from the same permits.

Bias-corrected Cramér’s V tests indicated that correlation between the covariates that we included in the models was weak (V <0.4), so it was not necessary for us to remove covariates from any models (Table 3). Variance inflation factors for covariates in the multivariate models were all <2, indicating that multicollinearity among these covariates was not an issue. The top model was without fixed effects (i.e., the null model), and this model accounted for nearly half of the WAICω (0.47; Table 3). The next three ranked models included primary activity and habitat alteration (both univariate models and the model including both covariates additively), and these models accounted for a total of 52% of the WAICω in the model set (Table 3). The parameter estimates for infrastructure and landscape modification activities were very large (i.e., in both Activity and Activity + AltHab models) and were the only parameters in the top models where the 95% CrIs of the parameter estimates did not encompass 0; however, these estimates also had very high uncertainty (Table 4; Figure S1, Supplemental Material). Additionally, the pd P values for the primary activity infrastructure and landscape modification parameters in the top-ranked models were very low, indicating that there was high certainty that the effect of these parameter estimates was in the same direction as the mean; this is not surprising considering that all nests exposed to infrastructure and landscape modification activities were successful (Table 4). In contrast, the other parameters in these top models had very high pd P values, which indicates high uncertainty that these parameter estimates were in the same direction as the mean (Table 4). Taken together, this evidence suggests that the covariates we tested were weak predictors of nest success.

Table 3.

Models assessing the relationship between anthropogenic activities and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.

Models assessing the relationship between anthropogenic activities and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.
Models assessing the relationship between anthropogenic activities and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.
Table 4.

Means, standard deviations, and 95% credible limits on the logit scale estimated from the top four models (total widely applicable information criterion weight = 0.992) examining the relationship between anthropogenic activity and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.

Means, standard deviations, and 95% credible limits on the logit scale estimated from the top four models (total widely applicable information criterion weight = 0.992) examining the relationship between anthropogenic activity and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.
Means, standard deviations, and 95% credible limits on the logit scale estimated from the top four models (total widely applicable information criterion weight = 0.992) examining the relationship between anthropogenic activity and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.

In this study, we found that a high proportion of bald eagle breeding pairs could fledge at least one young when exposed to different types of anthropogenic activities despite the activity being inconsistent with NBEMG recommendations. This was true at nests located in environments ranging from low to high levels of human development intensities. Comparisons of nest success before, during, and after years of activity also suggest that, generally, there was no apparent negative effect of anthropogenic activity on bald eagle nest success. Thus, our results indicate that bald eagles appear to be quite tolerant of human activity during the breeding season. Our modelling suggests that types of anthropogenic activity and nesting environment, whether physically altered by the activity or not, are poor predictors of nest success based on the null model carrying nearly half the WAICω and the CrIs of most parameter estimates in the top-ranked models not encompassing 0. This is likely largely due to similarly high nest success rates among all categories within each covariate.

The overall nest success rate of 84% that we estimated from our data was similar to that found in some bald eagle populations (e.g., South Carolina 82% [Wood et al. 1990], Florida 80% [Millsap et al. 2004], Louisiana 84% [Smith et al. 2017], and Kansas 91% [Winder and Watkins 2020]) but was notably higher than rates of other populations (e.g., Oregon 60% [Anthony et al. 1994], Texas 64% [Mabie et al. 1994], and Alaska 59% [Steidl 1994]). In our models, we tested types of anthropogenic activity, the environment surrounding nests, and whether that environment was physically altered by the activity. Several bald eagle studies have also examined these aspects in relation to human activity and their effects on nest success, and, although results vary, studies have generally demonstrated bald eagle resilience to disturbance. Some examples of types of anthropogenic activities where bald eagle nest success was similar between exposed and unexposed nests include seismic operations (which included high concentrations of airboat traffic; Linscombe et al. 1999), recreational activity (Mathisen 1968), and research activities (e.g., climbing nests to band birds; Grier 1969; Anthony et al. 1994). Fraser et al. (1985) compared the success of bald eagle nests located within and beyond 500 m of a range of types of human activities (e.g., vehicle and pedestrian traffic, primary roads, machinery, and recreation areas) and found no significant difference in success rates between nests less than and greater than 500 m from the activity. In addition, Fraser et al. (1985) also conducted intentional disturbance trials where observers visible to the nesting eagles walked toward the nest until the eagle was flushed and reported similar nest success rates between the experimental and control nests. Regarding the level of human development in the environment surrounding nests, Millsap et al. (2004) found that bald eagle nest success in Florida was identical in suburban and rural nests, and other studies also found no difference in bald eagle nest success between areas with low and high levels of human development (Gende et al. 1998; Goulet et al. 2021). Several bald eagle studies have also found similar nest success when the habitat surrounding the nest is physically altered by anthropogenic activities (e.g., logged versus unlogged areas; Anderson 1985; Gende et al. 1998). Although our study was not primarily designed to test success between nests exposed and unexposed to human activity, our small subset of nests that were monitored in years before and after the period of authorized activity showed no difference in success.

After the null model (top model), the second- to fourth-ranked models, which carried the majority of the remaining WAICω (52%), included primary activity and habitat alteration covariates. Despite the 95% CrIs of the parameter estimates for landscape modification and infrastructure activities excluding 0 and having pd P values of ≤0.004, CrIs in all cases were very wide, suggesting that these parameters have poor predictive power. This is likely a result of all nests exposed to landscape modification (n = 6) and infrastructure (n = 9) activities being successful in all nest-seasons. In our data, the landscape modification activities authorized during bald eagle breeding season in the six permits included one permit for the construction of a community park, one permit for plantings for site restoration, one permit for a prescribed burn, and three permits for tree removal. All of these activities, perhaps with the exception of the prescribed burn, are likely considered relatively benign disturbances compared with clear-cut logging, which we reported above as having similar nest success rates as observed in unlogged areas (Anderson 1985; Gende et al. 1998). Infrastructure activities authorized in the permits in our data included construction of new structures (e.g., stormwater conveyance channel and retention basin, wastewater treatment plant), modifications to existing structures (e.g., pumping and electrical stations, wastewater treatment plant), and soil boring for a utility grid followed by helicopter line stringing. Some of these activities appear to have the potential to be highly invasive, yet all bald eagle nests exposed to these anthropogenic activities were successful in every nest-season. Furthermore, of the 15 successful nest-seasons where nests were exposed to landscape modification and infrastructure activities listed above, the nests were in at least one of each of the primary environment categories (i.e., industrial, urban, suburban, rural, and natural). This demonstrates that bald eagle nests have high success rates when exposed to different types of human activities and in a range of levels of human development in the environments surrounding those nests.

It is important to note that the reproductive metric used in our study to evaluate the effects of authorized anthropogenic activities was nest success (i.e., fledging at least one young), and, although we show no negative effects, we did not examine whether those nests that were successful may have had reduced productivity (i.e., number of young fledged). In other bald eagle studies, in addition to success rates of disturbed and undisturbed nests being similar, researchers also found that productivity did not differ. For example, types of human activities where no significant difference in productivity was reported between exposed and unexposed nests include clear-cut logging (Gende et al. 1998), selective logging (Arnett et al. 2001), research activities (Grier 1969), and other habitat alterations (e.g., pastures, cultivated fields, clear-cuts, pine plantations, and residential areas; McEwan and Hirth 1979). In fact, Linscombe et al. (1999) found that productivities were significantly higher in all years in bald eagle nests in areas with seismic operations (including high concentrations of airboat traffic) than in areas without seismic operations. Additionally, Millsap et al. (2004) reported no difference in productivity between suburban and rural bald eagle nests, and Goulet et al. (2021) found higher productivity in nests built on farmlands or close to patch edges where the surroundings had high percentages of human land use than observed in isolated trees or remote rural land-use areas. In contrast, several studies have demonstrated reduced productivity in bald eagle nests exposed to a variety of types and levels of human activity (Anthony and Isaacs 1989; Steidl 1994; Fraser and Anthony 2008). This suggests that anthropogenic activities do have the potential to negatively affect bald eagle population dynamics. With that said, although we did not assess potential reductions in productivity that could have occurred in response to the anthropogenic activities, our definition for nest success indicates that for every successful nest, a minimum of one young is fledged, which is only slightly less than the mean productivity of 1.15 young per occupied nest for the contiguous United States (i.e., excluding the southwest region; USFWS 2016b). Furthermore, if we account for the proportion of unsuccessful nests estimated from our data (i.e., based on our estimate of 84% nest success), the minimum productivity of the nests in our study would only be slightly less at 0.84 young fledged per occupied nest.

An important consideration with our study is that the analyses were limited to data from incidental take permits issued by the USFWS, the nature of which has potential for biases. For example, given that these permits specifically relate to human activities, which are more likely to occur in areas with higher levels of human development, we might expect nests located in more remote areas to underrepresent what might be considered typical nest locations in the general bald eagle breeding population. In fact, 37% of nests monitored in our data were in areas with lower human land use (i.e., 13% natural and 24% rural environments) compared with nearly double (63%) the number of nests in areas with higher levels of human development (i.e., industrial, urban, and suburban environments). Historically, bald eagle nesting sites were typically in more remote areas (Stalmaster 1987; Gerrard and Bortolotti 1988); however, given the rapid rate of human encroachment on bald eagle habitat coupled with the fourfold increase in the bald eagle population since 2009 (Zimmerman et al. 2022; Castle et al. 2023), a significant proportion of nesting territories might be expected to be in closer proximity to human activity. Indeed, studies have found that bald eagles are now nesting in relatively high densities near human activity (Mundahl et al. 2013; Goulet et al. 2021). Additionally, we could further explain the preponderance of bald eagle nests in developed areas by the concept of generational habituation, whereby juveniles imprint on nest areas near human activity, and they select similar nest sites when reproductively mature. When this occurs over successive generations, the population expands into areas formerly considered suboptimal nesting habitat (Guinn 2013). Another possible shortfall in our inferences resulting from the data coming from these permits is that one of the criteria for inclusion in the data was that the nest was only exposed to a single authorized activity. The purpose of this criterion was to ensure that when nest failure occurred, we could identify the anthropogenic activity that may have influenced that failure (i.e., if there was more than one authorized activity in the same nest-season, we could not confirm which activity [or both] may have been related to the nest failure). Therefore, we can only report that bald eagle nest success was high when exposed to a range of human activities but cannot posit whether multiple anthropogenic activities may indeed lead to nest failure.

This study was unique in that our data spanned a very large area (i.e., much of the contiguous United States) and tested the effects of a wide range of anthropogenic activities in many different environments. An important objective for the USFWS issuing permits for incidental disturbance of bald eagle nests is to document and account for take associated with the failure of breeding pairs to fledge young to ensure compliance with the preservation standard (USFWS 2016c) and thresholds for eagle management units and local area populations. The assumption when a permit is issued is that the nest identified in the permit will be unsuccessful, and thus, the population would be debited by the loss of productivity from nest failure or abandonment. This amount is 1.33 young, which is the 80th quantile estimate of the mean productivity of 1.15 young for bald eagle-occupied nesting territories across the contiguous United States, excluding the southwest region (USFWS 2016b). Clearly, the permitted bald eagle nests have high success rates, so assuming nest failure may result in overestimation of take. Perhaps, given these high success rates, adjusting the debited take to account for the proportion of successful nests predicted by our analyses (84%) would provide a more realistic estimate of incidental take from nest disturbance. Alternatively, a more conservative approach is to account for the uncertainty in the nest success estimate by adjusting the debited take using the 20th quantile estimate of 81%. Additionally, considering the high success rate of the bald eagle nests in our data and that all authorized activities were within the buffer distances currently recommended in NBEMG (USFWS 2007b), a revision of the prescribed nest buffer distances may be warranted to reduce unnecessary permitting and lower the potential social burdens of nest protection (Watts and Byrd 2022). We could achieve this calibration of distance buffers either through categorical reduction of recommended distances or context-dependent reductions (e.g., shorter distance buffers in urban environments). Our findings provide further evidence that the growing contingent of bald eagles nesting in human-developed environments tolerate anthropogenic activities to a degree that they can nest successfully at rates comparable to those of the general U.S. population.

Please note: The Journal of Fish and Wildlife Management is not responsible for the content or functionality of any supplemental material. Queries should be directed to the corresponding author for the article.

Data S1. Microsoft Excel file of data and metadata from bald eagle nests listed under permits issued in the United States by the U.S. Fish and Wildlife Service from 2009 to 2021 to authorize activities that may cause incidental disturbance of breeding bald eagles Haliaeetus leucocephalus and that did not adhere to the National Bald Eagle Management Guidelines.

Available: https://doi.org/10.3996/JFWM-23-007.S1 (16 KB)

Table S1. Categories and subcategories included in the primary activity covariate used in models assessing the relationship between anthropogenic activities and bald eagle Haliaeetus leucocephalus nest success in the United States from 2009 to 2021.

Available: https://doi.org/10.3996/JFWM-23-007.S2 (19 KB)

Figure S1. Marginal posterior density distributions of intercept and β coefficient estimates from the null (no fixed effects), primary activity (Activity), habitat alteration (AltHab), and Activity + AltHab models examining the success of bald eagle Haliaeetus leucocephalus nests exposed to anthropogenic activities in the United States from 2009 to 2021 (see Table 4 and Table S1, Supplemental Material). Note that the skewed marginal posterior density distributions for the primary activity infrastructure and landscape modification parameters are due to all nests exposed to these activities being successful.

Available: https://doi.org/10.3996/JFWM-23-007.S3 (599 KB)

Reference S1. Bangs EE, Bailey TN, Berns VD. 1982. Ecology of nesting bald eagles on the Kenai National Wildlife Refuge, Alaska. Pages 47–54 in Ladd WN, Schempf PF, editors. Proceedings of a symposium and workshop on raptor management and biology in Alaska and western Canada. Anchorage, Alaska: U.S. Department of the Interior.

Available: https://doi.org/10.3996/JFWM-23-007.S4 (295 KB)

Reference S2. [USEPA] U.S. Environmental Protection Agency. 1972. Consolidated DDT hearings: opinion and order of the administrator. Federal Register 37:13369–13376.

Available: https://doi.org/10.3996/JFWM-23-007.S5 (16 KB) and https://archives.federalregister.gov/issue_slice/1972/7/7/13366-13376.pdf

Reference S3. [USFWS] U.S. Fish and Wildlife Service. 2007a. Endangered and threatened wildlife and plants; removing the bald eagle in the lower 48 states from the list of endangered and threatened wildlife. Federal Register 72:37346–37372.

Available: https://doi.org/10.3996/JFWM-23-007.S6 (324 KB) and https://www.govinfo.gov/content/pkg/FR-2007-07-09/pdf/07-4302.pdf

Reference S4. [USFWS] U.S. Fish and Wildlife Service. 2007b. National Bald Eagle Management Guidelines. Washington, D.C.: U.S. Fish and Wildlife Service.

Available: https://doi.org/10.3996/JFWM-23-007.S7 (148 KB) and https://www.govinfo.gov/content/pkg/FR-2007-07-09/pdf/07-4302.pdf

Reference S5. [USFWS] U.S. Fish and Wildlife Service. 2009. Eagle permits; take necessary to protect interests in particular localities. Federal Register 74:46836–46879.

Available: https://doi.org/10.3996/JFWM-23-007.S8 (315 KB) and https://www.govinfo.gov/content/pkg/FR-2009-09-11/pdf/E9-21589.pdf

Reference S6. [USFWS] U.S. Fish and Wildlife Service. 2016a. Eagle permits; revisions to regulations for eagle incidental take and take of eagle nests. Federal Register 81:91494–91554.

Available: https://doi.org/10.3996/JFWM-23-007.S9 (593 KB) and https://www.govinfo.gov/content/pkg/FR-2016-12-16/pdf/2016-29908.pdf

Reference S7. [USFWS] U.S. Fish and Wildlife Service. 2016b. Bald and golden eagles: population demographics and estimation of sustainable take in the United States, 2016 update. Washington, D.C.: Division of Migratory Bird Management.

Available: https://doi.org/10.3996/JFWM-23-007.S10 (3.645 MB) and https://www.fws.gov/sites/default/files/documents/bald-and-golden-eagles-status-report-and-sustainable-take.2016.pdf

Reference S8. [USFWS] U.S. Fish and Wildlife Service. 2016c. Programmatic Environmental Impact Statement for the Eagle Rule Revision. Washington, D.C.: Division of Migratory Bird Management.

Available: https://doi.org/10.3996/JFWM-23-007.S11 (4.044 MB) and https://www.fws.gov/sites/default/files/documents/programmatic-environmental-impact-statement-permits-to-incidentally-take-eagles.pdf

Financial and logistical support was provided by the USFWS. We thank the USFWS regional staff for compiling and screening permit data, including T. Borneman, R. Collins, D. Endrizzi, M. Kaplin, U. Kirkpatrick, D. Leal, K. McDonnell, M. Rheude, and K. Watts. We thank K. Kritz and E. Savage for assistance in developing the data template and the USFWS regional staff for critical review of earlier versions of the template. We also thank the Associate Editor, J. Eisaguirre, and an anonymous reviewer for their valuable comments that helped improve the manuscript.

Any use of trade, product, website, or firm names in this publication is for descriptive purposes only and does not imply endorsement by the U.S. Government.

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The findings and conclusions in this article are those of the author(s) and do not necessarily represent the views of the U.S. Fish and Wildlife Service.

Author notes

Citation: Gedir JV, Millsap BA, Howell PE, Wittig TW, White HM, Bjerre ER. 2023. Nest success of bald eagles exposed to anthropogenic activities in the United States. Journal of Fish and Wildlife Management 14(2):283–293; e1944-687X. https://doi.org/10.3996/JFWM-23-007

Supplemental Material