Scott A. Rush

Understanding the Potential Impacts of Global Climate Change on Marsh Birds in the Gulf of Mexico Region

Global climate change is expected to significantly affect coastal ecosystems worldwide. For tidal marsh birds of the Gulf of Mexico, the extent of these impacts on future population dynamics is unknown. Here, we present information on our current understanding of marsh bird responses to climate change, identify gaps in that understanding, and propose ways of improving our ability to predict impacts on avian populations. Our understanding of how Gulf Coast avian populations will respond to environmental drivers such as sea-level rise, precipitation patterns, and hurricanes is limited, and detailed local and regional studies linking avian biology to wetland processes are needed. Impacts of wetland change on marsh bird species will be optimally assessed and forecasted within an adaptive framework, making use of process-driven studies that include models designed to elucidate patterns in avian biology and wetland dynamics. Further, because management and conservation efforts are implemented at local or site-specific scales, we recommend that process-driven studies incorporate hierarchical structures, nesting local efforts within a regional context. Implementing this research program will prove fundamental in furthering our understanding of avian population dynamics within the changing Gulf of Mexico environment.

Short-Term Effects of Fire on Breeding Birds in Southern Appalachian Upland Forests

Abstract We investigated how variation in fire severity (control or no fire; low, medium, and high severity fires) and interval (1–2 years vs. 3–6 years after fires) affected habitat and avian abundance, species diversity, richness, and evenness in the southern Appalachian Mountains. Fire severity and interval had significant implications for both habitat and avian communities. Species richness within 2 years of fires was on average 26% higher in areas receiving medium and high severity treatments than in unburned control units. Species diversity and species richness were markedly greater 3–6 years after fires within high severity treatments (12 and 44%, respectively), compared to unburned controls. Relative abundance and species evenness did not vary with fire severity or time since fire. The short-term effects of low severity fires, or high severity fires with short rotation periods (≤2 years) may have limited positive effects on avian communities. Facilitation of disturbance regimes including mid to high severity fires, which foster uneven-aged forests, can be an effective conservation tool for restoring avian communities.

Variation in the Nesting Habits of Clapper Rails in Tidal Marshes of the Northern Gulf of Mexico

Abstract. To document nest survival and habitat differences in the nesting habitats of Clapper Rails (Rallus longirostis) in tidal marshes of the northern Gulf of Mexico, we monitored 76 active nests within the Pascagoula River Marsh Coastal Preserve (a freshwater-dominated estuary) and the Grand Bay National Estuarine Research Reserve (a marine-influenced estuary) in coastal Mississippi from 2005 to 2007. During 2006, we measured the height of each Clapper Rail nest, sampled vegetation at active Clapper Rail nests and at random locations, and measured the distance to the nearest tidally influenced body of water and the average height and density of vegetation. Early in the breeding season, the average nest height was lower at the Pascagoula (36 cm) than at Grand Bay (60 cm), but, as the season progressed, nest height increased at the Pascagoula only. Within both estuaries, Clapper Rail nest sites were more structurally complex than at random locations and were associated with a greater diversity of vegetation. Overall, daily survival rates of Clapper Rail nests were relatively high (0.97–0.99), with the majority of nest loss apparently the result of tidal flooding. Our results suggest that where diverse habitat was available, Clapper Rails varied the height of their nests as a mechanism to avoid nest loss from tidal flooding. Habitat alteration from factors such as sea-level rise and coastal development may lead to lower nest success because of a loss of diverse nesting habitat.

Isotopic Ratios Reveal Mixed Seasonal Variation Among Fishes from Two Subtropical Estuarine Systems

Characterizing dietary resources and species interactions in estuaries is challenging, particularly when considering the dynamic nature of these ecosystems, the ranges in body sizes of species, and the potential for trophic roles to vary with ontogeny. We examined the influence of season and location on relationships between body size and δ15N, δ13C, and δ34S values across a range of fishes from two subtropical estuaries. The results suggest that isotopic values of estuarine fishes are independent of body size. However, seasonal variation propagated throughout the assemblage as the majority of fishes integrated different δ15N, δ13C, or δ34S values. The absence of δ15N–, δ13C–, and δ34S–body size relationships suggests that either (1) dietary preference of these fishes do not shift within the range of body sizes sampled, (2) these fishes shift to an alternate diet that is not isotopically distinct, or (3) that spatial and temporal variation in isotopic signatures of prey negate any size-based relationships. Seasonal variability in the isotopic values of these fishes suggests either movement to an alternative habitat or a shift in organic matter source associated with the transition of dry to wet seasons. Moreover, variance distributions of the best-fit models indicate that seasonal dietary preferences of conspecifics do not vary over moderate spatial scales. Seasonal variability among fishes in these estuaries suggests plasticity in feeding strategies that may afford greater adaptive flexibility to these species in response to changes in food availability resulting from variable environmental conditions.

Loss of seasonal variability in nekton community structure in a tidal river: evidence for homogenization in a flow-altered system

Modifications to riverine systems that alter freshwater inflow to downstream estuarine habitats have resulted in altered patterns of nekton distribution and abundance. To examine how nekton assemblages respond to variable hydrologic patterns, we used trawl and seine survey data to compare the seasonal trends (dry vs. wet season) expected of a natural system to those of a river with regulated flow discharges that often magnify high flow events. Nekton assemblages differed between seasons in a representative natural system, similar to other estuaries of the region. For example, assemblage differences were characterized by significantly higher abundance and richness in trawl surveys, and significantly higher richness in seine surveys in the wet relative to the dry season. These seasonal trends were dampened in the altered system. Species important in defining seasonal dissimilarities in both systems were characterized as estuarine resident species, including Anchoa mitchilli, Menidia spp., Cynoscion arenarius, and Trinectes maculatus, yet were observed largely to have opposing seasonal trends in abundance between the two rivers. Our comparison provides evidence that flow modifications result in a loss of natural seasonal variability in estuarine nekton assemblages, but additional investigations of flow-altered systems are needed to confirm these findings.

Effective use of Data from Marshbird Monitoring Programs for Conservation Decision-Making

Abstract. Monitoring programs aimed at understanding the population trends of secretive marshbirds can be altered to benefit from the creative interplay between predictions, designs and models, and provide the template for doing so. Effective application of information to decision making typically requires integration of several types of information in a common framework, including “found” data and retrospective studies, innovative sampling designs and the use of hierarchical data structures. Hierarchical and state-space modeling provide a unified modeling structure for such designs and data. These ideas are illustrated with the problem of investigating and mitigating the effects of climate change on secretive marshbirds in coastal North America. How both ecological theory and available data can be used to provide predictions about the impacts of regional and local climate changes on these avian communities are illustrated.

Stopover Site Fidelity by Tennessee Warblers at a Southern Appalachian High-elevation Site

Abstract We examined stopover site fidelity by Tennessee Warblers (Oreothlypis peregrina) at two Tennessee banding stations (Whigg Meadow and Big Bald) operated during fall migration, ∼1,000 km from the nearest breeding areas. We captured and banded 4,324 Tennessee Warblers at Whigg Meadow from 1999 to 2008 with 14 individuals (0.3%) recaptured in subsequent years. We banded 5,514 Tennessee Warblers at Big Bald from 2003 to 2008 where, despite relatively close geographical proximity to Whigg Meadow (<150 km between sites), no individuals were recaptured outside of the initial capture year. These inter-annual recaptures, to our knowledge, reflect the highest reoccurrence of a Nearctic-neotropical migratory passerine at a single stopover site. Our results provide evidence that passerine stopover site fidelity may occur at considerable distances from both breeding and wintering areas, and differ between geographically similar stopover sites.

Management Practices Used in Agricultural Drainage Ditches to Reduce Gulf of Mexico Hypoxia

Agricultural non-point sources of nutrients and sediments have caused eutrophication and other water quality issues in aquatic and marine ecosystems, such as the annual occurrence of hypoxia in the Gulf of Mexico. Management practices have been implemented adjacent to and in agricultural drainage ditches to promote their wetland characteristics and functions, including reduction of nitrogen, phosphorus, and sediment losses downstream. This review: (1) summarized studies examining changes in nutrient and total suspended solid concentrations and loads associated with management practices in drainage ditches (i.e., riser and slotted pipes, two-stage ditches, vegetated ditches, low-grade weirs, and organic carbon amendments) with emphasis on the Lower Mississippi Alluvial Valley, (2) quantified management system effects on nutrient and total suspended solid concentrations and loads and, (3) identified information gaps regarding water quality associated with these management practices and research needs in this area. In general, management practices used in drainage ditches at times reduced losses of total suspended solids, N, and P. However, management practices were often ineffective during storm events that were uncommon and intense in duration and volume, although these types of events could increase in frequency and intensity with climate change. Studies on combined effects of management practices on drainage ditch water quality, along with research towards improved nutrient and sediment reduction efficiency during intense storm events are urgently needed.

Impacts of Diet on Thiamine Status of Lake Ontario American Eels

Abstract The Lake Ontario–upper St. Lawrence River (LOUSL) population of American Eels Anguilla rostrata (hereafter, “eels”) was once one of the most important groups of the species but is now in a state of serious decline. Given that thiamine deficiency has been observed in almost all of the top predators in Lake Ontario, we assessed the potential that a diet-induced thiamine deficiency associated with consumption of Alewives Alosa pseudoharengus could be involved. Muscle thiamine was measured in eels from throughout the LOUSL corridor and was compared with putative threshold effect levels established from the literature. Mirex concentrations were used to separate Lake Ontario-resident eels from non-Lake Ontario-resident eels. Stable isotope analyses of eel muscle samples and potential prey, including Alewives, were combined with mixing model software to infer the diets consumed by Lake Ontario eels. Although residence in Lake Ontario was associated with a significant decline in muscle thiamine concentra...

Alligator wrestling: morphological, molecular, and phylogenetic data on Odhneriotrema incommodum (Leidy, 1856) (Digenea: Clinostomidae) from Alligator mississippiensis Daudin, 1801 in Mississippi, USA

Based on specimens collected from harvested American alligator Alligator mississippiensis Daudin, 1801 in Mississippi, USA, novel molecular data for both nuclear ribosomal genes (18S, ITS1-5.8S, ITS2, and 28S) and mitochondrial genes (cytochrome c oxidase subunit 1 and nicotinamide adenine dinucleotide dehydrogenase subunit 1) are provided for Odhneriotrema incommodum (Leidy, 1856), a trematode of the family Clinostomidae Lühe, 1901 infecting A. mississippiensis and the Florida spotted gar Lepisosteus platyrhincus DeKay, 1842. This represents the first sequencing data available for the genus Odhneriotrema and the subfamily Nephrocephalinae Travassos, 1928. Additionally, the results of phylogenetic analyses, additional morphometric data, a photomicrograph, and a line drawing supporting the present identification of O. incommodum are provided. These data will aid in elucidating the life cycle of O. incommodum through molecular identification of larval stages as well as understanding the evolutionary history of Clinostomidae and its subfamilies. Implications for the currently accepted organization of the Clinostomidae are discussed.