As one of the largest birds of prey in North America, the bald eagle is a large bird with a brown body and a white head and tail. The name is derived from its scientific name which translates to white-headed sea eagle. As sea animals, bald eagles are commonly found near large water bodies. However, the bird is indigenous to the North American area, where the bird has been recorded to range from Alaska and Canada through the US and Northern Mexico. Due to human activities, however, the bald eagle population experienced a dramatic drop in the 1960 (Simon et al., 2020). For instance, the bird species was extensively hunted by people (by shooting them and trapping them as varmints). Furthermore, exposure to environmental pollutants like DDT and PCB that were the product of human activities reduced their population to an endangered species (Thakur & Pathania (2020). Case in point, there were only 52 known breeding pairs in Michigan by 1961 (Simon et al., 2020). Though numerous efforts have been made to increase the population of the species (with success), it still remains a fact that understanding what happened to bald eagles is key to reversing the species accelerated extinction that is happening around the world. Gaining a deeper understanding of bald eagles is essential for two reasons. First, the birds are the national symbol for the US. Therefore, there is an inherent incentive to avoid the bird’s extinction. Secondly, human activities affect all species in the ecosystem. However, it is impossible to understand all of the impacts. Therefore, indicator species are an essential part of how researchers understand changes to the ecosystem and how they are related to specific human activities.
The Great Lakes Basin and its Importance
The Great Lakes Basin occupies over 23,000 km2 of fresh water, holds approximately 90% of the US’s freshwater. According to Howard & Gerber (2018), apart from collecting and accumulating water (and other contaminants) from a large area, its basin extends a significant geographic area. Note, however, that the basin is not a single ecological system. Instead, it is a combination of plains, tributaries, terrestrial and inland wetlands, shoreline, lakes, and costal marshes (Howard & Gerber, 2018). In other words, the biological diversity in these ecosystems support a significant number of human activities and livelihood, both in the US and abroad. Unfortunately, the complex food webs involved are not only difficult to understand, but also make the entire ecosystems highly sensitive to abrupt changes. These changes are both anthropogenic and natural.
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For instance, the human population around the basin and those who depend on it is continuously growing. Fuentes (2013) wrote a dissertation on the bald eagles and their relationship to the emerging risks from the Great Lakes basin ecosystem. The report documents that the are supports at least 38 million people, all of whom use the water for most of their needs, from agriculture, to municipal and industrial use. The lakes have been recorded to host over 250 species of fishing, which have a value of $4 billion in sports and commercial fishing (Fuentes, 2013). The Great Lakes are also a host to a local commercial shipping industry and tourism. All these changes have resulted in significant repurposing of available land, each with their negative impact. Some of these are overfishing, eutrophication, and the introduction of invasive species (Fuentes, 2013). While these are the direct changes introduced, there are other significant indirect changes with their unique consequences.
A good example is the impact of global warming and the significant increase of the carbon dioxide concentration in the atmosphere. The temperature changes will not only increase the temperature of the Great Lakes, but also reduce their levels (Fuentes, 2013). The consequences will be numerous. For instance, the changes in the ecosystem will increase stress on different species at all trophic levels. Secondly, these changes will be accompanied with changes in human activities to accommodate and minimize the impact of climate change on their lives. Note that these factors are not independent. Instead, they continuously interact in ways that cannot be predicted by researchers. Therefore, a model for understanding the impact of changes in the ecosystem and solutions to future problems are needed.
Why Bald Eagles?
There are numerous species in the Great Lakes basin and in North America. Furthermore, each of the species is sensitive to the anthropogenic and natural changes in the specific ecosystems that they can provide the required knowledge and insight. However, these species are only specific to their ecosystems and fail to provide actionable information in other ecosystems. What is required is a species that is a strong integrator of different food webs at more than one trophic level (Ferguson, 2019). As a prerequisite, such a species would need to be widely distributed in the ecosystem or geographical region of interest and have an inherent human value that can be sampled in research. In other words, what is needed is an indicator species. In Northern America, especially the Great Lakes Basin, the bald eagle is the only bird that qualifies as an indicator species. Not only does the bald eagle have a low tolerance to environmental changes, it is also sensitive to certain stressors, each of which are valuable in research and practice (Fuentes, 2013). However, that is not the only reason bald eagles are the chosen indicator species for this study.
Some of the changes, both natural and anthropogenic, take long to show their effects, especially at lower trophic levels. Therefore, if there is a need to mitigate negative consequences of changes before they have widespread impacts, it is essential to study species at high trophic levels through biomagnification. Bald eagles support such research directions due to their long lives and slow reproduction cycles. An adult bald eagle will live up to 28 years in the wild and 36 years when in captivity. As a result, though the birds are susceptible to chronic impacts of pollutants, understanding them early will help not only save them, but also enact policies that will help preserve lower trophic levels. For instance, the abrupt drop in the bald eagle population in the 1960s was attributed to two main factors: hunting by people (by shooting them and trapping them as varmints) and exposure to environmental pollutants like DDT and PCB that were the product of human activities reduced their population to an endangered species (Thakur & Patania, 2020). The result was the implementation of policies and regulations that have recently been reported to have saved the birds from extinction. By extension, the same policies, such as the banning of pollutants like DDT and PCB also help relieve stress on other species at lower trophic levels, thus helping entire ecosystems recover to a larger extent.
Impact of Human Activity on Bald Eagles
The previous sections have attempted to summarize the impact of human activity on the bald eagles and how that affects the ecosystem. An even important considerations, however, is the impact of specific human activities during specific periods in the lives of bald eagles and how it still threatens the future survival of the species. According to Slankard et al. (2021), the lives of bald eagles are generally classified into nesting and non-nesting periods. During the nesting period, the birds will migrate to areas with high supply of food, such as large lakes and coastlines. The nesting period is also a time where the birds are highly sensitive and susceptible to human activity.
For instance, when the eagles are disturbed by human activity in their nesting period, they may construct their nests poorly or abandon them fully (Slankard et al., 2021). Failed nesting attempts mean that the population of the species will not recover even as environmental stressors increase. Additionally, human activities pose a significant risk during the incubation and hatching period, which may lead to damaging the eggs or injured chicks when the adults quickly flee from their nests. Furthermore, the young are also not acclimated to human activity, especially environmental noise. As a result, they may jump from their nests before they can fly, thus risking their lives and exposing them to other dangers.
In contrast, the non-nesting period is where bald eagles are least sensitive to human activity. Even then, the birds are far from being risk-free. For instance, due to habitat loss, human activities like construction sites keep the birds from hunting or taking shelter. As a result, the birds are forced to move to sub-optimal sites. When the nesting period comes, the risks increase significantly, as described above.
Environmental Pollutants and Biomagnification
Due to increased levels of human activity in the last few centuries, the levels of chemicals in the environment have been increasing. These contaminants, especially lead, mercury, arsenic, and cadmium, not only affect the species but also humans who rely on the same ecosystems and food webs for sustenance and for commercial purposes. Burger & Gochfield (2009) conducted a study where they measured the levels of different metals in the feathers of different birds at different trophic levels. Among the birds tested in the study, only two (bald eagles which occupy high trophic levels and eiders that are at the lowest trophic levels) are relevant to the subject of this paper. Burger & Gochfield (2009) discovered that bald eagles had the highest concentrations of heavy metals like arsenic, lead, mercury, and chromium. Furthermore, the concentration of heavy metal within the same species was spatially distributed. For instance, Burger & Gochfield (2009) reported that the bald eagles on Adak was higher than those on Amchitka, both islands in southwest Alaska. In contrast, eiders at the lowest trophic levels had the lowest concentrations of the same heavy metals. Such results pointed to the growing worries about the spread of heavy metals as pollutants at all levels of the food webs. Since humans also occupy high trophic levels, consuming food and products from the same regions for extended periods of time would also leave them vulnerable to bioaccumulation.
However, what is important in this paper is the impact of bioaccumulation on the populations of bald eagles in North America. According to Fuentes (2013), the increase in the concentration of heavy metals in the bodies of bald eagles has both lethal and sub-lethal effects. These include, but not limited to increased susceptibility to diseases and other environmental stressors and direct mortality. A definite lethal effect recorded has been a reduction in the fecundity of the bird species and changes in behavior, thus impacting their reproduction and future survival. For a species that has slow reproductive cycles, these lethal and sub-lethal effects have significant impact on their populations. Though regulations and policies implemented have helped reduce the level of heavy metals in the ecosystem, and by extension the bald eagles, it remains a fact that it will be a long time before the levels reduce in the environment.
What Can Be Done
Though the previous sections presented a larger picture view of bald eagles, their relationship to the North American ecosystems, and what can be done to mitigate the consequences of the associated changes, no solution has been presented in whole. Therefore, ensuring the continuity of an indicator species like the bald eagle will provide deeper insight into what can be done to save other trophic levels. The recent success to recover the population of bald eagles point to different solutions. First, government and community intervention has proven to be essential in controlling anthropogenic factors. What remains is gaining a deeper understanding of the impact of human activity on the bald eagles, and by extension the ecosystems they represent. Though there are no direct solutions, it is clear that increasing awareness of the known consequences is the first step in controlling the continuous degradation of the environment due to human activity.
Conclusion
In summary, this paper has presented a position supporting the need to gain a deeper understanding of bald eagles for two reasons. First, the birds are the national symbol for the US. Therefore, there is an inherent incentive to avoid the bird’s extinction. Secondly, human activities affect all species in the ecosystem. However, it is impossible to understand all of the impacts. Therefore, indicator species are an essential part of how researchers understand changes to the ecosystem and how they are related to specific human activities. This paper, therefore, presented a new perspective to understand the species, not just as a preservative measure as they are endangered, but also because they provide necessary knowledge to save the entire ecosystem.
References
Burger, J., & Gochfeld, M. (2009). Comparison of arsenic, cadmium, chromium, lead, manganese, mercury and selenium in feathers in bald eagle (Haliaeetus leucocephalus), and comparison with common eider (Somateria mollissima), glaucous-winged gull (Larus glaucescens), pigeon guillemot (Cepphus columba), and tufted puffin (Fratercula cirrhata) from the Aleutian Chain of Alaska. Environmental monitoring and assessment , 152 (1), 357-367.
Ferguson, L. (2019). Evaluating the (mis) application of the indicator species concept in Canadian environmental impact assessment.
Fuentes, L. (2013). LONG-TERM BALD EAGLE MONITORING: ASSESSING EMERGING RISKS TO THE GREAT LAKES ECOSYSTEM BY EVALUATING IMPACTS TO TERTIARY PREDATORS.
Simon, K. L., Best, D. A., Sikarskie, J. G., Pittman, H. T., Bowerman, W. W., Cooley, T. M., & Stolz, S. (2020). Sources of mortality in bald eagles in Michigan, 1986–2017. The Journal of Wildlife Management , 84 (3), 553-561.
Slankard, K. G., Patton, M. D., & Watts, B. D. (2021). Home Range of a Breeding Male Bald Eagle (Haliaeetus leucocephalus) Tracked via Satellite Telemetry in Kentucky. Northeastern Naturalist , 28 (1), 106-113.
Howard, K., & Gerber, R. (2018). Impacts of urban areas and urban growth on groundwater in the Great Lakes Basin of North America. Journal of Great Lakes Research , 44 (1), 1-13.
Thakur, M., & Pathania, D. (2020). Environmental fate of organic pollutants and effect on human health. In Abatement of Environmental Pollutants (pp. 245-262). Elsevier.
