Thomas C Michot

Endozoochory of seeds and invertebrates by migratory waterbirds in Oklahoma, USA Given their abundance and migratory behavior, waterbirds have major potential for dispersing plants and invertebrates within North America, yet their role as vectors remains poorly understood. We investigated the numbers and types of invertebrates and seeds within freshly collected faecal samples (n = 22) of migratory dabbling ducks and shorebirds in November 2008 in two parts of Lake Texoma in southern Oklahoma. Killdeer Charadrius vociferus were transporting a higher number and diversity of both plants and invertebrates than the green-winged teal Anas carolinensis. Ten plant taxa and six invertebrate taxa were identified to at least genus level, although viability was not confirmed for most of these taxa. Bryozoan statoblasts (from four species not previously recorded from Oklahoma) were especially abundant in killdeer faeces, while the ostracod Candona simpsoni was detected as a live adult in torpor in the teal faeces. Cyperaceae and Juncaceae were the most abundant plant families represented and Cyperus strigosus seeds germinated after extraction from killdeer faeces. This snapshot study underlines the importance of waterbirds as vectors of passive dispersal of many organisms and the need for more research in this discipline. RESUMEN Endozoocoria de semillas e invertebrados por aves acuáticas migratorias en Oklahoma, USA Debido a su abundancia y a sus migraciones, las aves acuáticas tienen un gran potencial como dispersores de plantas e invertebrados en el Norte de América, pero su papel como vectores apenas se ha estudiado. Se investigó la cantidad y diversidad de invertebrados y semillas presentes en heces frescas (n = 22) de patos nadadores y limícolas recogidas en noviembre 2008 en dos zonas del Lago Texoma en el sur de Oklahoma. El chorlitejo colirrojo Charadrius vociferus transportó un número y diversidad de plantas y de invertebrados más alto que la cerceta americana Anas carolinensis. Se identificaron diez taxones de plantas y seis de invertebrados, al menos a nivel de género, aunque para la mayoría de los taxones no se comprobó su viabilidad. Los estatoblastos de briozoos fueron especialmente abundantes en las heces de chorlitejos, mientras que en las heces de una cerceta se recuperó vivo un ejemplar adulto del ostrácodo Candona simpsoni. Las familias Cyperaceae y Juncaceae fueron las más representadas entre las semillas recuperadas, y las semillas de Cyperus strigosus germinaron tras extraerse de las heces. Este breve estudio subraya la importancia de las aves acuáticas como vectores de dispersión para muchos organismos, y la necesidad de más investigaciones en esta línea.

Long distance dispersal (LDD) of propagules is an important determinant of population dynamics, community structuring and biodiversity distribution at landscape, and sometimes continental, scale. Although migratory animals are potential LDD vectors, migratory movement data have never been integrated in estimates of propagule dispersal distances and LDD probability. Here we integrated migratory movement data of two waterbird species (mallard and teal) over two continents (Europe and North America) and gut retention time of diff erent propagules to build a simple mechanistic model of passive dispersal of aquatic plants and zooplankton. Distance and frequency of migratory movements diff ered both between waterbird species and continents, which in turn resulted in changes in the shapes of propagule dispersal curves. Dispersal distances and the frequency of LDD events (generated by migratory movements) were mainly determined by the disperser species and, to a lesser extent, by the continent. e gut retention time of propagules also exerted a significant eff ect, which was mediated by the propagule characteristics (e.g. seeds were dispersed farther than Artemia cysts). All estimated dispersal curves were skewed towards local-scale dispersal and, although dispersal distances were lower than previous estimates based only on the vector fl ight speed, had fat tails produced by LDD events that ranged from 230 to 1209 km. Our results suggest that propagule dispersal curves are determined by the migratory strategy of the disperser species, the region (or fl yway) through which the disperser population moves, and the propagule characteristics. Water-birds in particular may frequently link wetlands separated by hundreds of kilometres, contributing to the maintenance of biodiversity and, given the large geographic scale of the dispersal events, to the readjustment of species distributions in the face of climate change.

Diets of wintering redheads (Aythya americana) have been studied in the past, but none of the previous studies compared diets of the upper gastrointestinal tract to determine if they differed due to sex, age, location, year, or time of year. We compared diets of redheads collected over seagrass beds at Chandeleur Sound, Louisiana (n = 287) and Laguna Madre, Texas (n = 495) during the winters of 1987–1988 to 1989–1990. We found no significant differences due to location , year, sex, age, or time of year. Halodule wrightii (shoalgrass) was the primary food of birds from both locations and comprised 74% (dry mass) of the combined esophageal and proventricular contents. Mollusks were of secondary importance and accounted for 21% (18% gastropods, 3% pelecypods) of the diet. Because wintering redheads depend almost entirely on a single seagrass species and associated fauna, protection and enhancement of Halodule beds should be the highest conservation priority within the winter range of this species.

We report the presence of arbuscular mycorrhizae (AM) in Spartina alterniflora Loisel roots. Roots were sampled for AM in field-collected and greenhouse-maintained Spartina patens (Aiton) Muhl. and S. alterniflora, the dominant species of Louisiana's brackish and saline marshes, respectively. Previous reports of AM association in these Spartina sp. are limited and conflicting. Field-collected S. alterniflora had minimal AM (2.4%), whereas 39.5% of the S. patens roots examined were AM colonized. Greenhouse conditions of reduced salinity [3 parts per thousand (ppt)] appeared to increase AM association for S. patens compared with field samples. AM occurrence varied significantly among the three sample sites. Our results of low AM association in S. alterniflora differ from previous studies and confirm one previous report of AM in S. patens. Confirming AM association previously thought to be nonexistent in S. alterniflora marshes is a necessary first step in determining if AM influence zonation and competition.

Accelerated eutrophication is common to many freshwater and marine environments and often co-occurs with the presence of anthropogenic chemicals. However, the toxic effects of common chemical stressors such as herbicides in the presence of elevated nutrients are

Understanding the consequences of hurricanes on the food resources available to neotropical-nearctic migrant songbirds may provide important insight into the effects of hurricanes on migratory populations. During autumn migration 2006 we investigated the foraging ecology of two species of insectivorous migrants, Blue-gray Gnatcatcher (Polioptila caerulea) and Yellow Warbler (Dendroica petechia), and the availability of their foraging substrates and arthropod food resources in two coastal forests in western Louisiana, which were impacted to different degrees by Hurricane Rita in autumn 2005. Both migrant species attacked prey on bark substrates significantly more frequently, and on live foliage less frequently, in severely damaged forest than in lightly damaged forest (x 2 tests, P , 0.05). However, both species attacked prey on bark less than expected given its availability (i.e., migrants avoided bark), and attacked prey on live foliage more than expected given its availability (i.e., migrants selected live foliage), in severely damaged forest (x 2 tests, P , 0.03). Branch-clipping revealed that arthropod biomass on live hackberry (Celtis laevigata) and sweet acacia (Acacia farnesiana) branches was significantly higher in severely damaged forest than in lightly damaged forest (Mann-Whitney test, P , 0.01). However, because live foliage was significantly less available in severely damaged forest, overall food availability for migrants was lower in severely damaged forest than in lightly damaged forest. Migrant use of, and arthropod biomass on, bark and live-foliage substrates were thus dependent on the availability of those substrates, which differed between sites as a result of hurricane-related habitat disturbance. These results demonstrate that severe hurricane disturbance reduces food availability for insectivorous songbirds during migratory stopover by reducing the availability of preferred foraging substrates.

Diets of wintering redheads (Aythya americana) have been studied in the past, but none of the previous studies compared diets of the upper gastrointestinal tract to determine if they differed due to sex, age, location, year, or time of year. We compared diets of redheads collected over seagrass beds at Chandeleur Sound, Louisiana (n = 287) and Laguna Madre, Texas (n = 495) during the winters of 1987–1988 to 1989–1990. We found no significant differences due to location , year, sex, age, or time of year. Halodule wrightii (shoalgrass) was the primary food of birds from both locations and comprised 74% (dry mass) of the combined esophageal and proventricular contents. Mollusks were of secondary importance and accounted for 21% (18% gastropods, 3% pelecypods) of the diet. Because wintering redheads depend almost entirely on a single seagrass species and associated fauna, protection and enhancement of Halodule beds should be the highest conservation priority within the winter range of this species.

Aerial surveys are often used to quantify sizes of waterbird colonies; however, these surveys would benefit from a better understanding of associated biases. We compared estimates of breeding pairs of waterbirds, in colonies across southern Louisiana, USA, made from the ground, fixed-wing aircraft, and a helicopter. We used a marked-subsample method for ground-counting colonies to obtain estimates of error and visibility bias. We made comparisons over 2 sampling periods: 1) surveys conducted on the same colonies using all 3 methods during 3–11 May 2005 and 2) an expanded fixed-wing and ground-survey comparison conducted over 4 periods (May and Jun, 2004–2005). Estimates from fixed-wing aircraft were approximately 65% higher than those from ground counts for overall estimated number of breeding pairs and for both dark and white-plumaged species. The coefficient of determination between estimates based on ground and fixed-wing aircraft was 0.40 for most species, and based on the assumption that estimates from the ground were closer to the true count, fixed-wing aerial surveys appeared to overestimate numbers of nesting birds of some species; this bias often increased with the size of the colony. Unlike estimates from fixed-wing aircraft, numbers of nesting pairs made from ground and helicopter surveys were very similar for all species we observed. Ground counts by one observer resulted in underestimated number of breeding pairs by 20% on average. The marked-subsample method provided an estimate of the number of missed nests as well as an estimate of precision. These estimates represent a major advantage of marked-subsample ground counts over aerial methods; however, ground counts are difficult in large or remote colonies. Helicopter surveys and ground counts provide less biased, more precise estimates of breeding pairs than do surveys made from fixed-wing aircraft. We recommend managers employ ground counts using double observers for surveying waterbird colonies when feasible. Fixed-wing aerial surveys may be suitable to determine colony activity and composition of common waterbird species. The most appropriate combination of survey approaches will be based on the need for precise and unbiased estimates, balanced with financial and logistical constraints.

Waterfowl management on breeding grounds focuses on improving nest success, but few studies have compared waterfowl nest success and factors affecting nest survival along a wetland gradient and simultaneously identified nest predators. We monitored nests (n ¼ 195) of common pochards (Aythya ferina) in Trebon Basin Biosphere Reserve, Czech Republic, during 1999–2002. Daily nest survival rates (DSRs, logistic-exposure) declined from island (0.985, 95% confidence interval, 0.978–0.991) to overwater (0.962, 0.950–0.971) and terrestrial (0.844, 0.759– 0.904) nests. The most parsimonious model for DSRs included habitat class (DSRs: island. overwater. terrestrial) and nest visibility. Nest survival was improved by reduced nest visibility, increased water depth, and increased distance from the nest to habitat edge in littoral habitats. On islands, nest success increased with advancing date and increased distance to open water. A model of constant nest survival best explained the data for terrestrial nests. There were no observer effects on DSRs in any habitat. In 2003, artificial nests (n ¼ 180; 120 contained a wax-filled egg) were deployed on study plots. The model that best explained variation in DSRs for artificial nests included only 1 variable: habitat class (DSRs: island ! overwater. terrestrial). Mammalian predation of artificial nests (by foxes [ Vulpes vulpes] and martens [ Martes spp.]) was more likely in terrestrial habitats than in littoral habitats or on islands. By contrast, corvids and marsh harriers (Circus aeruginosus) prevailed among predators of overwater and island nests. Our data indicate that artificial islands and wide strips of littoral vegetation may represent secure breeding habitats for waterfowl because those habitats allow nests to be placed in areas that are not accessible to, or that are avoided by, mammalian predators. Management actions should be aimed at preserving these habitats. This, along with creation of new artificial islands, could help to enhance breeding productivity of pochards and possibly other waterfowl species inhabiting man-made ponds. (JOURNAL OF WILDLIFE MANAGEMENT 70(3):784–791; 2006)

Redheads, Aythya americana, concentrate in large numbers annually in traditional wintering areas along the western and northern rim of the Gulf of Mexico. Two of these areas are the Laguna Madre of Texas and Chandeleur Sound of Louisiana. We collected data on 54,340 activities from 103 redhead flocks in Texas and 51,650 activities from 57 redhead flocks in Louisiana. Males and females fed similarly, differing neither in levels of feeding (percent of all birds in flock that were feeding) (p>0.90) nor in percentages of birds feeding by diving, tipping, dipping, or gleaning from the surface (p>0.10). The foraging level of redheads in the upper Laguna Madre region was relatively constant throughout two winters. Foraging of redheads in early winter in Louisiana was significantly greater than redhead foraging in the upper Laguna Madre, but by late winter, foraging by redheads in Louisiana had declined to the same level as that shown by redheads foraging in the upper Laguna Madre. The overall foraging level of redheads from Chandeleur Sound was greater (41%) than that of redheads in the upper Laguna Madre (26%), yet it was quite similar to the 46% foraging level reported for redheads from the lower Laguna Madre. Redheads in the upper Laguna Madre region of Texas fed more by diving than did those in the Chandeleur Sound and the lower Laguna Madre. Diving increased in frequency in late winter. Greater reliance by redheads on diving in January and February indicates that the birds altered their foraging to feed in deeper water, suggesting that the large concentrations of redheads staging at this time for spring migration may have displaced some birds to alternative foraging sites. Our results imply that the most likely period for food resources to become limiting for wintering redheads is when they are staging in late winter.

Diurnal time-activity budgets were determined for wintering redheads (Aythya americana) from estuarine seagrass beds in Louisiana (Chandeleur Sound) and Texas (Laguna Madre) and from ponds adjacent to the Laguna Madre. Activities differed (p<0.0001) by location, month, and diurnal time period. Resting and feeding were the most frequent activities of redheads at the two estuarine sites, whereas drinking was almost nonexistent. Birds on ponds in Texas engaged most frequently in resting and drinking, but feeding was very infrequent. Redheads from the Louisiana estuarine site rested less than birds in Texas at either the Laguna Madre or freshwater ponds. Redheads in Louisiana fed more than birds in Texas; this was partially because of weather differences (colder temperatures in Louisiana), but the location effect was still significant even when we adjusted the model for weather effects. Redheads in Louisiana showed increased resting and decreased feeding as winter progressed, but redheads in Texas did not exhibit a seasonal pattern in either resting or feeding. In Louisiana, birds maintained a high level of feeding activity during the early morning throughout the winter, whereas afternoon feeding tapered off in mid-to late-winter. Texas birds showed a shift from morning feeding in early winter to afternoon feeding in late winter. Males and females at both Chandeleur Sound and Laguna Madre showed differences in their activities, but because the absolute difference seldom exceeded 2%, biological significance is questionable. Diurnal time-activity budgets of redheads on the wintering grounds are influenced by water salinities and the use of dietary fresh water, as well as by weather conditions, tides, and perhaps vegetation differences between sites. The opportunity to osmoregulate via dietary freshwater, vs. via nasal salt glands, may have a significant effect on behavioral allocations.

Accelerated eutrophication is common to many freshwater and marine environments and often co-occurs with the presence of anthropogenic chemicals. However, the toxic effects of common chemical stressors such as herbicides in the presence of elevated nutrients are not well understood for most aquatic flora, particularly vascular species. To provide insight, field-collected Vallisneria americana Michx. (wild celery) were sequentially exposed to three nutrient concentrations for 3 months and then to nominal 11 and 110 microg L(-1) atrazine for 96 h. Nutrient concentrations (combined NH(4)(+), NO(2)(-), NO(3)(-), PO(4)(-)) were based on ambient concentrations in the St. Johns River (FL) and ranged from 0.013 to 0.668 mg L(-1). Nutrient pretreatment potentiated the toxicity of atrazine as determined by chlorophyll fluorescence activity. Electron transport rates (ETR) were significantly less (48-59%) for plants pretreated with low and ambient nutrient levels in the presence of an average of 107.5-128.1 microg L(-1) atrazine. Significant ETR reductions were also observed for plants exposed to an average of 11.4 microg L(-1) atrazine after exposure to nutrients three times the ambient concentration in the St. Johns River. The results indicate the importance of considering the presence of nutrients in chemical hazard assessments, particularly for phytotoxicants and nontarget vascular plants.

The Chandeleur Islands represent the largest and oldest transgressive barrier island arc in the northern Gulf of Mexico. Generated by the transgressive submergence of the St. Bernard delta complex, the Chandeleur Islands form the protective geologic framework for one of the richest areas of salt marsh and seagrass flats in Louisiana. The Chandeleur barrier island arc is 60 km long

We report the presence of arbuscular mycorrhizae (AM) in Spartina alterniflora Loisel roots. Roots were sampled for AM in field-collected and greenhouse-maintained Spartina patens (Aiton) Muhl. and S. alterniflora, the dominant species of Louisiana’s brackish and saline marshes, respectively. Previous reports of AM association in these Spartina sp. are limited and conflicting. Field-collected S. alterniflora had minimal AM (2.4%), whereas 39.5% of the S. patens roots examined were AM colonized. Greenhouse conditions of reduced salinity (3 ppt) appeared to increase AM association for S. patens compared to field samples. Arbuscular mycorrhizae occurrence varied significantly among the three sample sites. Our results of low AM association in S. alterniflora differ from previous studies and confirm one previous report of AM in Spartina patens. Confirming AM association previously thought to be non-existent in S. alterniflora marshes is a necessary first step in determining if AM influen...

ABSTRACT We evaluated two marsh terracing restoration projects (GI=Galveston Island State Park, PM=Pierce Marsh) to compare nekton density and biomass between locations and among habitat types (open water pre-construction, open water post-construction, terrace marsh, terrace pond). Most (72%) animals collected were decapod crustaceans. Few differences in nekton abundance were observed over time (pre-construction versus post-construction open water). Comparisons of pre-construction to post-construction open water showed that the locations differed environmentally (e.g., turbidity) and in populations of nekton species. Density and biomass of gulf menhaden Brevoortia patronus and spot Leiostomus xanthurus in spring and density of white shrimp Litopenaeus setiferus in fall were higher at PM than GI, whereas densities and biomass of blue crab Callinectes sapidus, density of pink shrimp Farfantepenaeus duorarum, and biomass of brown shrimp Farfantepenaeus aztecus in the fall were higher at GI than PM. Despite location differences, constructing terraces appeared to benefit fishery species at both locations. Densities of brown shrimp, blue crab, white shrimp (fall), and pink shrimp (fall) and the biomass of brown shrimp, blue crab, and white shrimp (fall) were higher in terrace marsh than open water. Marsh terracing appears to be an effective tool for enhancing fishery habitat in degraded coastal systems.