Rice is the most common wetland crop in the world, and important for waterbirds and shorebirds worldwide, including the United States. In Louisiana, shorebirds use rice fields during spring migration, and are an important for foraging and refueling during migration. However, competing land uses and restoration projects may reduce the availability of rice fields, and impact the landscape that shorebirds use during migration. To determine how shorebirds use the landscape, I evaluated local and landscape factors affecting shorebird use of rice fields during spring migration in southwestern Louisiana. Using five habitat suitability zones (HSZs) based on rice density and canopy cover, I performed stratified random surveys at rice fields within each of the 5 HSZs. I surveyed 94 fields in 2008 and 85 fields in 2009. I quantified all habitat types within 3 km of each field, recorded habitat conditions during each visit, and recorded all shorebirds observed. Mixed modeling analyses indicated that shorebird density was primarily influenced by local field conditions: flooding extent (p<00001), the percent of the field perimeter bordered by trees (p=0.0075), surveyed rice field area (p<0.0001), and rice height (p<0.0001). Shorebirds responded positively to flooding extent, and negatively to tree border, field area, and rice height. Overall shorebird density was not influenced by any landscape variables at any scale (1, 1.5, 2, 2.5, or 3 km). The percent of non-rice crop (p=0.0437) and fallow land (p=0.0400) immediately adjacent to surveyed fields was a positive influence on density of the seven most common species, and HSZ was a positive influence on shorebird habitat use for 3 of the most common species or species groupings: Dowitchers (2 spp), Peeps (3 spp), and Yellowlegs (2 spp). These species comprised > 50 % of all birds observed, indicating the importance of HSZ for individual species. Rice density was significantly higher in HSZ4 and HSZ5, and the percent of forest (an alternate measurement of canopy cover) was significantly lower in HSZs 4 and 5. These results support the validity of the habitat suitability model. By maintaining rice production in the higher HSZs, suitable local habitat conditions would be provided for shorebirds.

Population growth for mallards (Anas platyrhynchos), and presumably other upland nesting ducks, in the Prairie Pothole Region is most sensitive to nest success, and nest success is most strongly influenced by predation. I evaluated the efficacy of reducing predator populations to improve nest success and increase local breeding populations of upland nesting ducks on township-sized (93.2 km2) management units in eastern North Dakota, USA, during 2005−2008. I also examined potential territorial limitations on local population growth for mallards. Trappers annually removed an average of 245 predators per trapped site. I monitored 7,489 nests on 7 trapped and 5 nontrapped sites, and I found nest success to be 1.4−1.9 times greater on trapped sites, depending on year. I surveyed an average of 621 wetlands twice annually and observed 3,674 blue-winged teal (A. discors), 3,227 mallard, 2,287 gadwall (A. strepera), 1,539 shoveler (A. clypeata), and 679 pintail (A. acuta) breeding pairs. I found little evidence that local breeding populations of upland nesting ducks increased following predator reduction. Defense of territories, which may limit local population growth, was most frequent during settling and declined as greater portions of local mallard populations commenced nesting. Territorial defense was strongly correlated to the ratio of breeding pairs to available wetland habitat, such that sites with higher pair densities had greater frequencies of territorial behavior. Hence, defense of territories may function to limit local breeding populations. Though predator reduction provides managers with an effective tool to improve nest success at large spatial scales, they should not rely on the practice to increase local breeding populations.

Mallards Anas platyrhnchos are arguably the most researched waterfowl species in North America. They exhibit great flexibility in certain breeding metrics such as timing of nest initiation and clutch size. A study on captive female Mallards (Batt and Prince 1979) fed ad libitum, held in identical breeding compartments, and paired with the same mate in each year of the study exhibited substantial variation in the timing of nest initiation within a given year, yet some individual females demonstrated consistency in initiation date among years. My objective was to examine breeding metrics such as timing of nest initiation and clutch size and to evaluate age-related productivity in conjunction with those metrics. More specifically, I wanted to know if individual females were consistent in first initiated nests among years. Secondly, I wanted to know if age affected both the timing of nest initiation and clutch size. From 2006-2009 nest searching crews found 2274 Mallard nests and captured 944 females using various trapping techniques. I found strong evidence for variation among birds within year. I failed to find a significant influence of individual variation among birds between years. Age was not significant in impacting when an individual nests. The effects of nest year were also tested but were not significant. For my clutch size analysis, all 944 females captured were used and categorized to an age group based on wing feather characteristics. Age, year, and julian date all had significant impacts on clutch size. After second year (ASY) females had 0.32 more eggs than second year (SY) females. Clutch size varied by year and declined seasonally, such that for every day of delay clutch size was reduced by 0.05 eggs. Mallards exhibit great flexibility in the timing of nest initiation for which they breed. However, approximately 36% of the females show consistency in their individual nesting dates which were prior to the mean annual initiation date. Some individuals consistently nested later than the mean annual initiation date. Nevertheless, there appears to be strong directional selection for early nesting.

The Louisiana Gulf Coast is an important wintering area for North American gadwall (Anas strepera). Conservation of winter habitat is a top priority of the Gulf Coast Joint Venture. Quantitative estimates of habitat use by wintering gadwall would help improve energetic demand models and subsequent estimates of habitat requirements. I used satellite telemetry (PTTs) to estimate winter habitat and refuge uses, spring migration chronology and corridors, as well as inter- and intra-regional winter movements of females. I used a split-plot MANOVA to evaluate the effects of individual females, female age, winter, hunt periods within winter, time of day, and all possible interactions among these explanatory variables on habitat use. I used a mixed model ANOVA to evaluate the effects of individual females, female age, winter, hunt periods within winter, time of day, and all possible interactions of these explanatory variables on refuge use. I used mixed models to evaluate the effects of hunt periods within winter, refuge use, winter, individual female, female age, and body condition at time of capture on intra-regional movements. Finally, I used a MANOVA to evaluate the effects of female age, spring of tracking, and body condition at time of capture on several spring migration parameters. I found that habitat use in winter 2007-08 was dominated by intermediate marsh, whereas habitat use during winter 2008-09 showed an increased dependence on freshwater marsh (P = 0.0001). Use of non-hunted refuges by adult females was greater when hunting season was open than when closed (P = 0.0061). I found no significant relationships among the explanatory variables and intra-regional movements (all Ps > 0.09). Peak migratory departure from the Louisiana Gulf Coast Chenier Plain occurred during late-March to early-April. HY females traveled a greater total migratory distance, spent more days migrating, used more stopovers, and arrived at inferred breeding locations later than did AHY females (all Ps ≤ 0.061). My results suggest that intermediate marsh is important for wintering gadwall; however, freshwater marsh may become important after tidal surge events. Finally, my migration data provides habitat managers with quantitative information to consider when implementing conservation programs and management practices.

Colonial nesting seabirds are threatened by habitat loss and degradation, human disturbance, predation, and climate change. Several species of conservation concern concentrate high percentages of their total U.S. populations in Louisiana breeding colonies. We studied seabirds, including Royal Terns, Sandwich Terns, and Black Skimmers, nesting on Isles Dernieres barrier islands along the Gulf coast of Louisiana. Two of the four islands in this chain host extensive seabird colonies and two do not. We used an experimental approach to test the hypothesis that large terns and skimmers are prevented from nesting on Trinity Island, the largest of the Isles Dernieres, by lack of social stimuli. Decoys and call broadcast attracted Royal Terns to visit experimental sites, but they did not nest. Sandwich Tern and Black Skimmer visits to the sites were not significantly affected by the social stimuli; however, isolated nesting attempts imply interest. Lack of colony establishment in response to the experiment indicates that social factors alone are not responsible for the lack of nesting by these species on Trinity Island. Scent station transects revealed the presence of raccoons, rats, and coyotes on two non-colony islands, and no mammalian predators on two colony islands, suggesting that seabirds avoid predator-infested areas. Least Terns were an exception, nesting on islands with mammalian predators. In 2008 and 2009, we monitored 53 and 80 Least Tern nests on Trinity Island and modeled nest success using logistic exposure. A subset of nests was protected by fences in each year (n= 3 in 2008, n= 19 in 2009). For unprotected nests, model-estimated nest success was 20% in 2008 and 53% in 2009. Fenced nest success was 83% and 49% in 2008 and 2009, respectively. We believe the increase in nest success between years reflects effects of Hurricanes Gustav and Ike on predator populations on Trinity Island. Rats and raccoons declined in surveys and anecdotal field observations. The impact of mammalian predators on this Least Tern population supports the hypothesis that predation limits seabird colonization of Trinity Island.

In Louisiana, the extensive loss and fragmentation of coastal marshes has prompted inquires into the impacts these processes may have on estuarine-dependant nekton. To date, research on nekton response to marsh loss and fragmentation has been limited to landscape-level studies which focus on the relationship between nekton productivity and the availability of marsh edge. These studies have relied on the assumption that marsh edges provide the same level of support to nekton regardless of the degree of surrounding marsh loss or fragmentation. This study tested this assumption by investigating the impacts of marsh loss and fragmentation on marsh-edge characteristics and their associated nekton assemblages. The effects of marsh loss at the 1 km2 scale were examined by stratifying three brackish marsh management units located in the Chenier Plain of western Louisiana into three 1 km2 treatment squares, each representing one of three levels of marsh loss: Low (10%-35% water), Medium (40%-65% water), and High (70-95% water). Within each treatment square, nekton assemblage (density, diversity, body condition) and marsh-edge characteristics (water quality, submerged aquatic vegetation biomass, sediment organic matter, and emergent stem density) were sampled concurrently at six randomly established sampling points during the spring and fall of 2008. Variables representing marsh loss and fragmentation were also quantified within 1 ha squares centered on each sampling point. Relationships between nekton assemblage characteristics and environmental variables were explored with a canonical correspondence analysis. Data analysis revealed differences in sediment organic matter, ha scale percent marsh, and ha scale fragmentation in the spring sampling season. The passage of Hurricane Ike between sampling seasons may explain why only ha scale percent marsh differed between treatments in the fall. Despite differences in these environmental variables between treatments, nekton assemblage characteristics were not found to differ between treatments. This may be partially explained by the lack of strong relationships between nekton assemblage characteristics and environmental variables as indicated by the canonical correspondence analysis. The results of this study do not indicate that nekton support provided by marsh edges is influenced by the degree of marsh loss at the 1 km2 scale.

Since 1982, the Louisiana Department of Wildlife and Fisheries (LDWF) has stocked Florida-strain largemouth bass (FLMB; Micropterus salmoides floridanus) to incorporate Florida alleles into native populations (NLMB; M. s. salmoides) and enhance recreational fishing opportunities. I collected habitat data and largemouth bass samples from 12 LDWF stocked reservoirs and disconnected oxbow lakes to examine the relationships between reservoir characteristics, genetic identity, relative weight (Wr), liver somatic index (LSI), parasite loads, and back-calculated length-at-age. I examined the relationships between water body and genetic identity with Wr, LSI, and back-calculated length-at-age by ANOVA. Parasite loads were analyzed with ordinal regression. Principle component analysis was used to reduce the dataset into a smaller number of principal components and group the study lakes as habitat types. I then used ANOVA to assess whether Wr, LSI, or length-at-age were influenced by genetic strain or habitat type as represented by the principal components and logistic regression to determine whether principal component influenced the abundance of NLMB or non-native largemouth bass. Although similar across bass strains, Wr, LSI, and length-at-age varied by lake (all P<0.0001). Parasite loads were not significantly different between years or among water bodies or genetic strain. Based on the ANOVA results, shallow, nutrient rich lakes with high chlorophyll a concentrations and large littoral zones appeared to promote high Wr and non-native largemouth bass. Conversely, northern largemouth bass were more prevalent, and Wr was lower, in lakes with dense vegetation. Aquatic macrophytes may reduce foraging efficiency of larger, piscivorous fish while increasing survival of young-of-the-year largemouth bass. Reservoirs with little vegetative cover may reduce natural recruitment of resident largemouth bass allowing rapid genetic introgression. These findings may improve our understanding of the effects of FLMB stocking activities and provide the opportunity to modify stocking protocols to better achieve the management goals of the largemouth bass program.

Marsh loss is a problem in many areas around the world. In Louisianas coastal marshes, where Spartina patens is the most common plant, restoration and management seek to slow wetland loss rates that average approximately 77.4 km2/year. To combat the problem, scientists and managers require tools to determine local causes and evaluate the effectiveness of management techniques. Current methods for identifying factors that limit productivity in marshes are too time-consuming or expensive for wide-spread, regular use. Critical values of elemental concentrations in plant tissue are widely used to diagnose mineral deficiencies and toxicities in agricultural crops, however. I used the chemical composition of leaf tissue from S. patens grown under controlled conditions to develop critical values of C:N ratio and concentrations of Na, Mn, and Ca to identify N limitation, salinity stress, and flooding stress, respectively. I tested these critical values and identified seasonal changes in leaf tissue chemistry in a field experiment where all three limiting factors fluctuated naturally. I also compared the leaf tissue chemistry of S. patens and Spartina alterniflora, the second most common plant in Louisianas coastal marshes, to facilitate comparisons between the species. Finally, I investigated the effects of flooding stress on above- and belowground biomass of S. patens. Aboveground biomass was reduced by low N-uptake, high salinity, and high flooding. Belowground biomass was reduced by increased flooding. In leaf tissue, C:N decreased with increasing N-availability and [Na] increased with increasing salinity. [Mn] and [Ca] in leaf tissue decreased with increased flooding. In the field study, C:N increased seasonally. Biomass was most highly correlated with [Na] in spring and with both [Na] and C:N in summer. In fall, leaf tissue composition appeared unrelated to biomass. Managers should take seasonal differences in leaf tissue composition and nutritional requirements into account when diagnosing the causes of limited production and when creating management plans. Leaf tissue should be collected in summer to diagnose limiting factors. To have the most impact, flooding should be used in late spring or early summer to reduce salinity and increase N-availability.

Seasonal overbank flooding in systems like the Atchafalaya River Basin (ARB) provides the opportunity for fishes in the mainstem to access off-channel areas on the floodplain. Typically, newly inundated floodplain habitats allow adult fishes to add biomass, avoid predation, and potentially, to reproduce. However, in systems like the ARB, the timing, duration, and magnitude of flooding infrequently coincides with known reproductive periods of many fishes assumed to be floodplain-dependent. To quantify the level of floodplain-exploitative fish reproduction in the ARB, I collected larval and juvenile fish with a variety of sampling gear that allowed estimates in both ultra-shallow (< 2-m) and continuously-inundated habitats (headwater lakes, canals, and bayous). A suite of water quality parameters, river stage, flow, and hours of daylight were used to gauge the influence of environmental phenomena on age-0 abundance during both inundation and drawdown. The results of the 19-month study suggest that many taxa do not rely on the floodplain to ensure high survivorship. Interestingly, the reproductive ecologies of many ARB fishes appeared to be largely independent of widespread connectivity. Although an increasing hydrograph appeared to enhance reproductive output, the interannual timing and intensity of spawning showed limited variability. Larval densities were also contrasted with the microcrustacean zooplankton (copepods and cladocerans) population to assess if a potential food limitation existed in the weeks and months following hatching. During the study, increased zooplankter abundance was typically preceded by elevated river-floodplain connectivity. Conversely, as floodwaters receded during the summer, zooplankton abundance declined to lowest levels observed during the study. Overall, there was limited synchronous overlap between the hatchlings of most fish taxa and their zooplankter prey. This could have potentially resulted in starvation and reduced annual recruitment. Yet, my analysis of the factors that regulate larval fish abundance in the ARB suggest that the density of zooplankton was highly significant although high numbers of larvae and zooplankton rarely coincided. Finally, I compared the intraday (morning vs. afternoon) density and mean length of larval fish at fixed sample sites. The results suggest that once-daily ichthyoplankton collections may fail to provide accurate density and length measurements for young fish populations.

Greater structural complexity is often associated with more diverse and abundant species assemblages. Biogenic reefs formed by the eastern oyster (Crassostrea virginica) are structurally complex in nature and have been recognized for their potential habitat value in estuarine systems along the Atlantic and Gulf of Mexico coasts. To determine how the structural complexity of newly created oyster reefs may influence the abundance and distribution of species, three objectives were established. First, to examine spatial and temporal patterns of nekton use at newly created oyster reefs, as well as the impact of wave exposure, six paired oyster reef and mud-bottom treatments at low and medium wave energy shorelines were sampled quarterly, from June 2009 to March 2010, at Caillou (Sister) Lake, Louisiana, using gill nets, seine, and substrate trays. Transient species showed seasonal shifts with no evidence of habitat preference. Resident species were consistently more abundant at oyster reefs than mud-bottom treatments. There were no patterns in nekton use that could be directly attributed to wave exposure. Second, to determine how changes within the structural complexity of newly created oyster reefs may influence nekton use, oyster reef treatments of various complexities were created and sampled using a drop sampler. The presence of oyster reefs per se was the most important factor determining nekton assemblages; newly created oyster reefs provided habitat for nekton assemblages, but there was little difference between reef treatments. Lastly, to determine how oyster reefs mediate predator foraging success, treatments of various complexities were created and trials executed in a laboratory setting using wild red drum (Scianops occelatus) and grass shrimp (Palaemonetes pugio). Foraging success was negatively correlated to the structural complexity of oyster reefs, indicating there may be a point above which increased complexity no longer increases the refuge value of the reef. These results show that oyster reefs may support a high abundance and diversity of resident nekton, but that after structure is introduced, further increasing structural complexity does not automatically increase species abundance and diversity, or the amount of refugia provided.