Do Small, Patchy, Constructed Intertidal Oyster Reefs Reduce Salt Marsh Erosion As Well As Natural Reefs?

One ecological service that oyster reefs provide is stabilization of shorelines through reduced wave energy and erosion from boat traffic, storms, and predominant wind direction. Additionally, increasing sedimentation can enhance the growth of emergent marsh vegetation which further stabilizes unconsolidated sediments. A 21 mo study of constructed (with only 30-35% coverage) and natural oyster reefs in 3 bayous in the Grand Bay National Estuarine Research Reserve (NERR) suggested constructed reefs benefit this retrograding deltaic ecosystem. The marsh edge adjacent to all constructed reefs was less eroded (mean = 0.043 m) than edges adjacent to natural reefs (mean = 0.728 m), although all natural and constructed sites, regardless of bayou, illustrated large variations in marsh edge growth. The marsh edge in constructed sites in one bayou retreated more than in the other bayous, most likely due to its coarser sediments, greater boat traffic, and its apparent higher energy location within the landscape. By the end of this study, the ecological function of constructed oyster reefs in all bayous, as measured by marsh edge erosion reduction, was equivalent or exceeded the function in nearby natural oyster reefs. The physical structure of the reef further served to reduce erosion and marsh loss and this approach may be useful for management of a retrograding deltaic estuarine ecosystem like the Grand Bay NERR

Population genetics of seaside Sparrow (Ammodramus maritimus) subspecies along the gulf of Mexico.

Seaside Sparrows (Ammodramus maritimus) along the Gulf of Mexico are currently recognized as four subspecies, including taxa in Florida (A. m. juncicola and A. m. peninsulae) and southern Texas (Ammodramus m. sennetti), plus a widespread taxon between them (A. m. fisheri). We examined population genetic structure of this Gulf Coast clade using microsatellite and mtDNA data. Results of Bayesian analyses (Structure, GeneLand) of microsatellite data from nine locations do not entirely align with current subspecific taxonomy. Ammodramus m. sennetti from southern Texas is significantly differentiated from all other populations, but we found evidence of an admixture zone with A. m. fisheri near Corpus Christi. The two subspecies along the northern Gulf Coast of Florida are significantly differentiated from both A. m. sennetti and A. m. fisheri, but are not distinct from each other. We found a weak signal of isolation by distance within A. m. fisheri, indicating this population is not entirely panmictic throughout its range. Although continued conservation concern is warranted for all populations along the Gulf Coast, A. m. fisheri appears to be more secure than the far smaller populations in south Texas and the northern Florida Gulf Coast. In particular, the most genetically distinct populations, those in Texas south of Corpus Christi, occupy unique habitats within a very small geographic range

Age-Related Differences in the Stopover of Fall Landbird Migrants on the Coast of Alabama

We estimated fat load, length of stopover, and rate of mass change for six Neotropical migrant landbird species at a site along the northern coast of the Gulf of Mexico. Swainson\u27s Thrushes (Catharus ustulatus), Gray Catbirds (Dumetella carolinensis), White-eyed Vireos (Vireo griseus), Red-eyed Vireos(V. olivaceus), Magnolia Warblers (Dendroica magnolia), and American Redstarts (Setophaga ruticilla) were captured on Fort Morgan Peninsula in coastal Alabama during fall migration, 1990 to 1992. In Swainson\u27s Thrushes, White-eyed Vireos, and American Redstarts, adults carried significantly higher fat loads than young birds, whereas no age-related differences in fat loads were evident in the other species. The likelihood of staying beyond the day of capture and the rate of change in body mass did not differ between age classes. One consequence of differences in fat load is reflected in flight range in relation to the Gulf of Mexico. On average, adult Swainson\u27s Thrushes, White-eyed Vireos, American Redstarts, and both age classes of Magnolia Warblers carried sufficient energy stores to complete a trans-Gulf flight, whereas young Swainson\u27s Thrushes, White-eyed Vireos, American Redstarts and both age classes of Gray Catbirds carried insufficient stores for such a flight, based on flight-performance simulations

Age-Related Timing of Migration: Geographic and Interspecific Patterns

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Passerine Migrants Respond to Variation in Predation Risk During Stopover

During travel, migrants may encounter unfamiliar habitats and predators and visit sites for which they lack information on predation risk. Temporary stops during migration permit only limited opportunities to gather information about risk, and other priorities, such as the need to forage, may restrict these opportunities. Under these conditions, the extent to which migrants respond to variations in predation risk is unclear. We studied small passerine birds during migratory stopover to determine whether their behaviour was related to variation in risk of capture by migrating birds of prey. We used two approaches, observational and experimental. Observations revealed that blue-grey gnatcatchers, Polioptila caerulea, and American redstarts, Setophaga ruticilla, moved deeper into oak shrubs as the number of sharp-shinned hawks, Accipiter striatus, at the site increased. Furthermore, blue-grey gnatcatchers moved at slower rates as counts of hawks increased. The experiment revealed that blue-grey gnatcatchers had lower rates of both movement and foraging after exposure to a gliding model hawk. These results provide evidence that predator avoidance remains a priority during migration and that migrants are able to assess risk to some extent during temporary stopover. In addition, the results suggest that predator avoidance behaviour may limit foraging opportunities during stopover by restricting habitat use

Distribution, Abundance, and Habitat Characterization of the Saltmarsh Topminnow, \u3ci\u3eFundulus jenkinsi\u3c/i\u3e (Everman 1892)

The saltmarsh topminnow (Fundulus jenkinsi) is federally listed as a Species of Concern due to a its rarity, impacts from human activities, and lack of information on its biology and ecology. From 2007 through 2008, we used Breder traps to fish the marsh edge on a falling tide in four regions from Louisiana through the Florida panhandle during winter, spring, and summer periods. Out of 2,108 Breder traps deployed, 661 F. jenkinsi were collected as far east as Escambia Bay, Florida, with Weeks Bay, National Estuarine Research Reserve (NERR), Alabama, yielding the highest F. jenkinsi abundance. Principal component analysis (PCA) was used to ordinate physical-chemical data into two meaningful components: a geomorphic axis (water depth, bank slope, and plant stem density) and a seasonal/spatial axis of species occurrence (water temperature, salinity, and turbidity). PCA showed a higher mean catch-per-unit-effort (CPUE) in environments comprised of low to moderate stem density (\u3c 25 stems/0.25 m-2), depth (\u3c 25 cm), bank slope (\u3c 15 degrees), turbidity (\u3c 30 NTU), and salinity (\u3c 16) coupled with spring and early summer water temperatures (\u3e 15 degrees C). F. jenkinsi CPUE was significantly higher in Spartina cynosuroides marsh edge compared with five other habitat types, even though it was one of the least sampled habitats. This species appears to be collected more frequently and in higher CPUE in small dendritic creeks off of main channels than suggested by our previous work in main channel edge habitat. This suggests that small creeks are important vectors for marsh access and supports the value of the dendritic nature of salt marshes to marsh residents

A precise water displacement method for estimating egg volume

Relationships between egg volume and an array of life-history traits have been identified for many bird species. Despite the importance of egg volume and the need for precise and accurate measurements, egg volume is usually estimated using a mathematical model that incorporates length and width measurements along with a shape variable. We developed an instrument that provides precise estimates of egg volume and can be easily used in the field. Using Clapper Rail (Rallus longirostris) eggs, we compared egg volumes measured using our instrument with estimates based on linear measurements. We found our instrument to be both precise and accurate. Compared with a method based on linear measurements of eggs, use of our instrument reduced variation in egg volume estimates by 1.6 cm3, approximately 8% of the volume of a Clapper Rail\u27s egg. Further advantages of our technique include ease of use, increased accuracy of field-based volume estimates, and increased resolution of variation in egg volume estimates. In addition, our technique does not require postdata collection processing time and did not influence hatching success. Also, for Clapper Rails and similar species, our technique can be combined with other techniques (e.g., egg flotation) so that both egg volume and embryonic stage can be estimated at the same time. © 2009 Association of Field Ornithologists

Trophic relationships of a marsh bird differ between gulf coast estuaries

Much of North America\u27s tidal marsh habitat has been significantly altered by both natural and man-made processes. Thus, there is a need to understand the trophic ecology of organisms endemic to these ecosystems. We applied carbon (δ13C) and nitrogen (δ15N) stable isotope analysis, along with isotope mixing models, to egg yolk, liver, and muscle tissues of clapper rails (Rallus longirostris) and their likely prey items. This analysis enabled us to explore variation in trophic niche and diet composition in this important marsh bird in two northern Gulf of Mexico tidal marshes that are river and ocean-dominated. For the river-associated estuary, δ13C and δ15N of egg yolks, liver, and pectoral muscle tissue samples provided evidence that clapper rails maintained a similar diet during both the winter and the breeding season. A trophic link between C3 primary productivity and the clapper rail\u27s diet was also indicated as the δ13C of clapper rail egg yolks related negatively with the aerial cover of C3 macrophytes. Clapper rails from the ocean-dominated estuary had a narrower trophic niche and appeared to be utilizing marine resources, particularly, based on modeling of liver stable isotope values. Variation in stable isotope values between egg yolk and liver/muscle in both systems suggests that endogenous resources are important for egg production in clapper rails. These results demonstrate that diet composition, prey source, and niche width of clapper rails can vary significantly across different estuaries and appear to be influenced by hydrological conditions. © 2010 Coastal and Estuarine Research Federation

Population Genetics of Seaside Sparrow (<i>Ammodramus maritimus</i>) Subspecies along the Gulf of Mexico

<div><p>Seaside Sparrows (<i>Ammodramus maritimus</i>) along the Gulf of Mexico are currently recognized as four subspecies, including taxa in Florida (<i>A. m. juncicola</i> and <i>A. m. peninsulae</i>) and southern Texas (<i>Ammodramus m. sennetti</i>), plus a widespread taxon between them (<i>A. m. fisheri</i>). We examined population genetic structure of this “Gulf Coast” clade using microsatellite and mtDNA data. Results of Bayesian analyses (Structure, GeneLand) of microsatellite data from nine locations do not entirely align with current subspecific taxonomy. <i>Ammodramus m. sennetti</i> from southern Texas is significantly differentiated from all other populations, but we found evidence of an admixture zone with <i>A. m. fisheri</i> near Corpus Christi. The two subspecies along the northern Gulf Coast of Florida are significantly differentiated from both <i>A. m. sennetti</i> and <i>A. m. fisheri</i>, but are not distinct from each other. We found a weak signal of isolation by distance within <i>A. m. fisheri</i>, indicating this population is not entirely panmictic throughout its range. Although continued conservation concern is warranted for all populations along the Gulf Coast, <i>A. m. fisheri</i> appears to be more secure than the far smaller populations in south Texas and the northern Florida Gulf Coast. In particular, the most genetically distinct populations, those in Texas south of Corpus Christi, occupy unique habitats within a very small geographic range.</p></div

Sampling localities, presumed subspecies and sample sizes of Seaside Sparrow used in the Gulf-wide analyses of population genetic structure.

a<p>Griscom <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112739#pone.0112739-Griscom2" target="_blank">[62]</a> noted that <i>sennetti</i> and <i>fisheri</i> from this area may intergrade, even though it is the type locality for <i>sennetti</i>.</p><p>Subspecific identities based on summary by Robbins <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112739#pone.0112739-Robbins1" target="_blank">[22]</a>. “Site #” refers to localities shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0112739#pone-0112739-g001" target="_blank">Fig. 1</a>.</p><p>Sampling localities, presumed subspecies and sample sizes of Seaside Sparrow used in the Gulf-wide analyses of population genetic structure.</p