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In 2010, the Deepwater Horizon oil spill released an estimated 4.9 million barrels of oil into the Gulf of Mexico, damaging coastal ecosystems. Seaside Sparrows (Ammospiza maritima)—a year-round resident of Gulf Coast salt marshes—were exposed to oil, as shown by published isotopic and molecular analyses, but fitness consequences have not been clarified. We monitored nests around two bays in Plaquemines Parish, Louisiana, USA from 2012–2017 to assess possible impacts on the nesting biology of Seaside Sparrows. A majority of nests failed (76% of known-fate nests, N = 252 nests, 3521 exposure-days) during our study, and predation was the main cause of nest failure (~91% of failed nests). Logistic exposure analysis revealed that daily nest survival rate: (1) was greater at nests with denser vegetation at nest height, (2) was higher in the more sheltered bay we studied, (3) decreased over the course of the breeding season in each year, and (4) was not correlated with either sediment polycyclic aromatic hydrocarbon concentrations or estimated predator abundance during the years for which we had those data. Although the Deepwater Horizon spill impacted other aspects of Seaside Sparrow ecology, we found no definitive effect of initial oiling or oiled sediment on nest survival during 2012–2017. Because predation was the overwhelming cause of nest failure in our study, additional work on these communities is needed to fully understand demographic and ecological impacts of storms, oil spills, other pollutants, and sea-level rise on Seaside Sparrows and their predators. [ABSTRACT FROM AUTHOR]

Many bird species exhibit both social monogamy and genetic polygamy. Rates of genetic polygamy (often reported as the proportion of nests containing extra-pair young) in socially monogamous species vary widely, stimulating much research into the potentially adaptive value of these behaviors. Similarly, adult and nestling sex ratios of bird populations are not infrequently male-biased, leading to questions of the adaptive value of a female's ability to influence sex ratios within her nest. Empirical data on both aspects of reproductive behavior, however, are still scarce for a majority of species even within relatively well-studied bird communities. We sampled DNA from nestling (n = 153) and adult (n = 121) Seaside Sparrows (Ammospiza maritima) at 58 nests in southeastern Louisiana from 2012 to 2017. We used microsatellite genotype analyses to discover that (1) ∼32% of nests contained broods with mixed paternity, and (2) ∼4% of broods contained evidence of mixed maternity. We sexed all birds via PCR and found a significant male bias among nestlings (62% of all nestlings were males). Prevalence of mixed paternity and male bias among nestlings did not appear to be related to site oiling status following the Deepwater Horizon oil spill, site context, timing within breeding season, or density of adult Seaside Sparrows or nests. Nonetheless, these results indicate a need for further work to understand the breeding biology of Seaside Sparrows. Muchas especies de aves muestran tanto monogamia social como poligamia genética. Las tasas de poligamia genética (muchas veces reportadas como la proporción de nidos que contienen un polluelo fuera de la pareja) en especies monógamas sociales es muy variable, lo que favorece la investigación en el potencial valor adaptativo de estos comportamientos. De la misma manera, las proporciones de sexo de adultos y de polluelos de las poblaciones de aves no son infrecuentemente sesgadas hacia los machos, lo que lleva a preguntarse sobre el valor adaptativo de la habilidad de la hembra en influir en las proporciones sexuales dentro de su nido. Datos empíricos en ambos aspectos de comportamiento reproductivo, sin embargo, son todavía escasos en la mayoría de especies aún dentro de comunidades de aves relativamente bien estudiadas. Muestreamos ADN de nidadas (n = 153) y adultos (n = 121) de chingolos Ammospiza maritima de 58 nidos del sudeste de Louisiana de 2021 al 2017. Utilizamos análisis genotípicos satelitales para descubrir que (1) ∼32% de los nidos contenían nidadas con paternidad mixta, y alrededor de (2) ∼4% de las nidadas contenían evidencia de maternidad mixta. Determinamos el sexo de todas las aves por medio de PCR y encontramos un sesgo masculino significativo en todas las nidadas (62% de todas las nidadas eran machos). La prevalencia de la paternidad mixta y el sesgo masculino entre las nidadas no parece estar relacionado con el estatus de contaminación del sitio después del derrame de petróleo del Deepwater Horizon, contexto del sitio, temporalidad al interior de la temporada reproductiva o densidad del adulto de chingolos Ammospiza maritima o de nidos. Sin embargo, estos resultados indican una necesidad de estudios posteriores para entender la biología reproductiva de los chingolos Ammospiza marítima. Palabras clave: pantano, Passerellidae, producción fuera de la pareja, reproducción fuera de la pareja, sesgo reproductivo, sistema reproductivo. [ABSTRACT FROM AUTHOR]

Mercury (Hg) concentrations and their associated toxicological effects in terrestrial ecosystems of the Gulf of Mexico are largely unknown. Compounding this uncertainty, a large input of organic matter from the 2010 Deepwater Horizon oil spill may have altered Hg cycling and bioaccumulation dynamics. To test this idea, we quantified blood concentrations of total mercury (THg) in Seaside Sparrows (Ammospiza maritima) and Marsh Rice Rats (Oryzomys palustris) in marshes west and east of the Mississippi River in 2015 and 2016. We also tested for a difference in THg concentrations between oiled and non-oiled sites. To address the potential confounding effect of diet variation on Hg transfer, we used stable nitrogen (δ 15 N) and carbon (δ 13 C) isotope values as proxies of trophic position and the source of primary production, respectively. Our results revealed that five to six years after the spill, THg concentrations were not higher in sites oiled by the spill compared to non-oiled sites. In both species, THg was higher at sites east of the Mississippi River compared to control and oiled sites, located west. In Seaside Sparrows but not in Marsh Rice Rats, THg increased with δ 15 N values, suggesting Hg trophic biomagnification. Overall, even in sites with the most elevated THg, concentrations were generally low. In Seaside Sparrows, THg concentrations were also lower than previously reported in this and other closely related passerines, with only 7% of tested birds exceeding the lowest observed effect concentration associated with toxic effects across bird species (0.2 µg/g ww). The factors associated with geographic heterogeneity in Hg exposure remain uncertain. Clarification could inform risk assessment and future restoration and management actions in a region facing vast anthropogenic changes., (© 2024. The Author(s).)

In marine species, the transcriptomic response to Deepwater Horizon (DWH) oil implicated many biochemical pathways, with corresponding adverse outcomes on organ development and physiological performance. Terrestrial organisms differ in their mechanisms of exposure to polycyclic aromatic hydrocarbons (PAHs) and their physiological challenges, and may reveal either distinct effects of oil on biochemical pathways or the generality of the responses to oil shown in marine species. Using a cross-species hybridization microarray approach, we investigated the transcriptomic response in the liver of Seaside Sparrows (Ammospiza maritima) exposed to DWH oil compared with birds from a control site. Our analysis identified 295 genes differentially expressed between birds exposed to oil and controls. Gene ontology (GO) and canonical pathway analysis suggested that the identified genes were involved in a coordinated response that promoted hepatocellular proliferation and liver regeneration while inhibiting apoptosis, necrosis, and liver steatosis. Exposure to oil also altered the expression of genes regulating energy homeostasis, including carbohydrate metabolism and gluconeogenesis, and the biosynthesis, transport and metabolism of lipids. These results provide a molecular mechanism for the long-standing observation of hepatic hypertrophy and altered lipid biosynthesis and transport in birds exposed to crude oil. Several of the activated pathways and pathological outcomes shown here overlap with the ones altered in fish species upon exposure to oil. Overall, our study shows that the path of oil contamination from the marine system into salt marshes can lead to similar responses in terrestrial birds to those described in marine organisms, suggesting similar adverse outcomes and shared machinery for detoxification., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)