Field Notes- Storms on the horizon: Former success breeds conservation optimism for the brown pelican

Brown pelicans are a symbol of wildlife conservation success. Photo Credit: Bradley Wilkinson

Exactly five decades ago, in 1970, the brown pelican (Pelecanus occidentalis) was federally listed under the Endangered Species Preservation Act (ESA) and in dire need of conservation action [1]. Populations in the Atlantic, Gulf of Mexico, and California had been plummeting for years as a result of organic pollutants such as DDT, which were thinning eggshells and causing extensive reproductive failure. Common in widely-used pesticides at the time, DDT would enter the environment via runoff (i.e. water that flows over land and into waterways rather than being absorbed as groundwater or evaporating) and accumulate in the food web. This meant that top predators, especially those that consume fish, were highly burdened with the chemicals from their prey. In part to popular science pieces such as Silent Spring, authored by preeminent ecologist and nature writer Rachel Carson, and the tireless efforts of researchers working in the few pelican colonies that remained, far-reaching bans on the agricultural use of these chemicals were implemented in 1972. Since that time, brown pelicans have undergone a remarkable recovery. Able to breed successfully again, populations in the southeastern U.S. were removed from listing in 1985, and the species as a whole was delisted in 2009. To this day, the example of the pelican stands as one of the most successful targeted conservation actions in the United States and is lauded as testament to the effectiveness of the ESA. Despite this well-earned victory, however, the world around the pelican has changed. On the fiftieth anniversary of this federal listing, there is cause for both celebration and concern regarding this iconic coastal seabird.

Deveaux Bank in South Carolina is an important habitat for seabird nesting, roosting and foraging and is threatened by human disturbance, erosion, and sea level rise. [Source]

Even during the DDT-era of widespread population declines, South Carolina remained one of the few places that pelicans were still able to persist in any numbers. In fact, some of the same locations where researchers first learned of the toxic effects of pesticides host breeding pelicans to this day. One of these special breeding colonies is Deveaux Bank. A sand island situated where the North Edisto River meets the Atlantic Ocean, the locally-poplar bank hosts a variety of breeding seabirds every summer, including pelicans, terns (Thalasseus spp.), laughing gulls (Leucophaeus atricilla), and black skimmers (Rhynchops niger), among several species of shorebird and wader. Starting in 2017, members of my lab and I have been outfitting adult pelicans at Deveaux Bank, as well as three other nearby colonies, with GPS satellite transmitters. Used to track the movements of animals and attached with a backpack-style harness, these devices provide us around twelve highly-accurate GPS points per day as the pelicans go about their daily lives. And because they are solar-powered, transmitters can last months and even up to years.

Identification tags are important for keeping track of individuals during research observations. GPS transmitters are able to track movements, but these tags allow researchers to keep track of their health and behavior. Photo Credit: Bradley Wilkinson

Some of the earliest work that we have completed from the project started out as ‘research of opportunity’. In the early fall of 2017, Hurricane Irma made landfall in southwestern Florida before advancing up the peninsula. As it weakened, it brought high winds and torrential rain to much of the American Southeast, including coastal sections of Georgia and South Carolina. As it happened, we had just started our GPS deployments on pelicans that summer, and so had a cohort of transmitted individuals that we could follow throughout the storm. Unsurprisingly, there is a scarcity of data on what exactly coastal organisms do during a hurricane. Generally, it is thought that an individual animal can exhibit one of two strategies; either a ‘cut and run’ behavior to flee the storm, or a ‘seek shelter’ behavior to wait out the bad weather. Over the next year, we began examining the movements of tracked pelicans and applying statistical models to their behavior to see if individuals had significantly changed behavior as Irma passed overhead. It seemed as though pelicans had decided to ‘seek shelter’ during Irma, but that was only one storm. Just before we considered publishing this work, we were hit with two more cyclones the following fall, Michael and Florence. As a result, we had opportunistically gathered data from GPS-tagged pelicans during three hurricanes over two years. Although out of our control, and cognizant of what this meant for human populations affected, we had acquired a very unique dataset. The odds of having GPS-tracked individual animals during three separate hurricane events were exceedingly slim, let alone in back-to-back years. Our data represented a significant step forward in understanding how coastal birds survive severe weather. After examining the tracks from pelicans across all three storms together, we found that pelicans generally employ the ‘seek shelter’ strategy, although the strength of this response is likely influenced by the relative strength of the storm (i.e. how dramatic the deviations of barometric pressure and wind velocity) [2]. Basically, pelicans would find a relatively protected spot as the storm approached, and then not leave to forage or move about until after the hurricane had passed.

Critically, brown pelicans generally chose coastal habitats for sheltering that are of conservation concern. These included places like barrier islands free of human development and large natural estuaries. Coastal habitats such as these are rapidly disappearing as human populations increase and develop them for recreation or tourism. This means there are few places left for seabirds like pelicans to breed, loaf, or shelter from weather. Unfortunately, the situation will likely only get worse as climate change and sea level rise further erode coastal ecosystems. Climate change could also alter how and when pelicans choose to migrate, exposing them to hurricanes of increasing intensity with few places to go. Current research in our lab is actively working to better understand this threat.

Photo Credit: Bradley Wilkinson

Pelicans nesting near urban cities like the ones that we study also deal with a host of other stressors. Older chemicals still present in the environment as well as newly-created contaminants are still an issue for these birds, for example perfluoroalkyl substances (PFASs), which preliminary data from our lab suggests is extremely high in birds from our South Carolina study colonies. Local and regional oil spills are an omnipresent concern, as illustrated by the 2010 Deepwater Horizon event. And even the diet of pelicans may be changing as a result of human activity.

Fifty years after being listed and declared recovered, brown pelicans can serve as an excellent model for how actionable conservation measures can dramatically improve wildlife populations. This lesson is important, and reason for optimism, as we face biodiversity declines across the globe. In the next fifty years, however, new threats are likely to emerge and new challenges will need to be faced. It is my hope that our research will help pelicans as much as the pioneers that saved the species not so long ago.

Bradley Wilkinson  (@Pelican_Paths) is a 3rd year Ph.D. candidate in the Department of Forestry and Environmental Conservation at Clemson University, and a member of the South Carolina Cooperative Fish and Wildlife Research Unit. His research focuses on the movement ecology of brown pelicans in the South Atlantic Bight and is interested in the spatial dynamics of marine vertebrate predators generally.

References

[1] Bureau of Sport Fisheries and Wildlife, Fish and Wildlife Service, Department of the Interior. Part 17—Conservation of endangered species and other fish and wildlife. Fed Regist 1970;35(106):8491–8. (http://ecos.fws.gov/docs/federal_register/fr21.pdf).

[2] Wilkinson, B. P., Satgé, Y. G., Lamb, J. S., & Jodice, P. G. R. (2019). Tropical cyclones alter short-term activity patterns of a coastal seabird. Movement Ecology, 7(30).

Main image credit: Bradley Wilkinson

Edited by Karli Chudeau

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