Seaside Sparrows and the Deepwater Horizon Oil Spill

Sabrina Taylor  |  6/3/2019 2:31:27 PM

Sabrina S. Taylor

Seaside Sparrows (Ammospiza maritima) are dependent on coastal saltmarshes throughout their life cycle. In the Gulf of Mexico, they do not migrate as the seasons change, so they are exposed to all disturbances that affect the marsh. Because of their close affinity with salt marshes, as well as their abundance (the sparrows number in the hundreds of thousands in the Louisiana salt marshes), they are a good indicator species for the effects of disturbances, such as oil spills and hurricanes.

LSU AgCenter scientists began studying Seaside Sparrows in the aftermath of the 2010 Deepwater Horizon oil spill as collaborators in the Coastal Waters Consortium — a group of scientists from several dozen universities tasked with examining the effect of the oil spill on the Louisiana salt marsh, the location where most of the oil that made landfall came ashore. Members of the consortium examined wide-ranging aspects of the marsh, including the effects on plants, fish, invertebrates and marsh sediments with an ultimate aim of synthesizing the data to form a cohesive picture.

A team of AgCenter professors, postdoctoral researchers, graduate students and field assistants was responsible for investigating the effect of the oil spill on marsh vertebrates, namely marsh rice rats and Seaside Sparrows. They chose these common species because of their abundance, their role as top predators, and their close association with the salt marsh. With the Seaside Sparrows, they have approached the effect of the oil spill in several ways. Early on, the team found that carbon from oil was present in diet items taken from the birds’ gut and was also incorporated into feather tissue at the molecular level. Later, researchers examined the expression of a gene (CYP1A) involved in metabolizing polycyclic aromatic hydrocarbons, a toxic component of oil. They found much greater expression of this gene in 2011, the year after the oil spill, on oiled sites as compared to nonoiled sites, suggesting that sparrows were exposed to and needed to metabolize toxins in oiled areas. However, they also found that this difference in expression among sites disappeared from 2012-2014. The team has extended this work by studying changes in the expression of several thousand other genes during 2011 to understand how the sparrows responded more generally. The results of this work should be published later this year.

The team is now examining how diet may have changed in Seaside Sparrows following the oil spill. By extracting DNA from sparrow gut and fecal samples, they can identify precisely what the sparrows are eating. Crabs (possibly their eggs), spiders and moths are favorite prey items, but preliminary data suggest there were no differences in diet between oiled and nonoiled sites. This result corroborates results obtained from collaborators who used stable isotopes and fatty acids to examine how the sparrows’ position in the food web may have changed following the oil spill. The team used nitrogen stable isotopes, which can be used to identify the position of an organism in the food. They also used carbon stable isotopes and fatty acids to distinguish the type of primary producer at the base of the food web, for instance, whether the primary producers were benthic/aquatic diatoms and bacteria or terrestrial plants, such as the common marsh grass Spartina alterniflora. In the sparrows, there was no difference between oiled and nonoiled sites for either of these stable isotopes or the fatty acids.

As an added challenge, Hurricane Isaac came through the field sites in late August 2012, completely inundating the marsh for two to three days. This storm also had an effect on the sparrows: CYP1A gene expression increased on all sites in 2013, suggesting that oil buried in the marsh was resuspended and redistributed to all areas; diet composition in 2013 changed; and sparrows shifted to a lower feeding level in the food web and more commonly ate prey that originated from benthic/aquatic rather than terrestrial primary producers. The latter two results may be an outcome of the marsh inundation, which may have caused part or most of the terrestrial insect community to die.

Did the oil spill have a population-level effect on sparrows? Collaborators are examining sparrow abundance and reproductive success from 2012-2017. Sparrow abundance steadily increased from 2012-2016 on all sites, but dropped in 2017. Reproductive success was consistently lower on oiled versus nonoiled sites. However, population-level effects are much more difficult to resolve because the areas that were oiled were also characterized by other confounding site attributes; for instance, they tended to be drier. Drier sites that aren’t flooded during high tides may result in different predator communities that could in turn affect nesting success. Future results on marsh rice rat abundance may show whether sparrow predators were more or less numerous on oiled sites, helping to resolve some of these confounding variables.

Sabrina S. Taylor is an associate professor and Weaver Brothers Distinguished Professor in the School of Renewable Natural Resources.

Acknowledgements: Phil Stouffer, Lee F. Mason Professor, School of Renewable Natural Resources; Andrea Bonisoli Alquati, a former postdoctoral student and currently an assistant professor at California State Polytechnic, Pomona; Anna Perez-Umphrey and Allison Snider, doctoral students with Sabrina Taylor; Jill Olin, a former LSU postdoctoral student, now at the Great Lakes Research Center at Michigan Technological University in Houghton; Mike Polito, an assistant professor in the LSU College of the Coast and Environment; and Stefan Woltmann, a former postdoctoral student and currently an associate professor at Austin Peay University in Clarksville, Tennessee, as well as his former master’s student Megan Hart. This research was made possible by a grant from the Gulf of Mexico Research Initiative. Data are publicly available through the Gulf of Mexico Research Initiative & Data Cooperative (GRIIDC) at https://data.gulfresearchinitiative.org.

For more information about research on the Seaside Sparrow, go to these articles:

All About Birds: Seaside Sparrow

Population Genetics of Seaside Sparrow along the Gulf of Mexico

(This article appears in the spring 2019 issue of Louisiana Agriculture.)

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Sabrina Taylor releases a Seaside Sparrow as part of her research. Photo by Phil Stouffer

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Seaside Sparrow. Photo by Phil Stouffer

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Laura Southcott searches for Seaside Sparrow nests in the Louisiana marsh. Photo by Phil Stouffer

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A Seaside Sparrow nest in the marsh. Photo by Phil Stouffer

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