François Bolduc

Relationships Between Wintering Waterbirds and Invertebrates, Sediments and Hydrology of Coastal Marsh Ponds

Abstract We studied relationships among sediment variables (carbon content, C:N, hardness, oxygen penetration, silt-clay fraction), hydrologic variables (dissolved oxygen, salinity, temperature, transparency, water depth), sizes and biomass of common invertebrate classes, and densities of 15 common waterbird species in ponds of impounded freshwater, oligohaline, mesohaline, and unimpounded mesohaline marshes during winters 1997-98 to 1999-2000 on Rockefeller State Wildlife Refuge, Louisiana, USA. Canonical correspondence analysis and forward selection was used to analyze the above variables. Water depth and oxygen penetration were the variables that best segregated habitat characteristics that resulted in maximum densities of common waterbird species. Most common waterbird species were associated with specific marsh types, except Green-winged Teal (Anas crecca) and Northern Shoveler (Anas clypeata). We concluded that hydrologic manipulation of marsh ponds is the best way to manage habitats for these birds, if the hydrology can be controlled adequately.

EFFECTS OF STRUCTURAL MARSH MANAGEMENT AND SALINITY ON INVERTEBRATE PREY OF WATERBIRDS IN MARSH PONDS DURING WINTER ON THE GULF COAST CHENIER PLAIN

Aquatic invertebrates are important food resources for wintering waterbirds, and prey selection generally is limited by prey size. Aquatic invertebrate communities are influenced by sediments and hydrologic characteristics of wetlands, which were affected by structural marsh management (levees, water-control structures and impoundments; SMM) and salinity on the Gulf Coast Chenier Plain of North America. Based on previous research, we tested general predictions that SMM reduces biomass of infaunal invertebrates and increases that of epifaunal invertebrates and those that tolerate low levels of dissolved oxygen (O2) and salinity. We also tested the general prediction that invertebrate biomass in freshwater, oligohaline, and mesohaline marshes are similar, except for taxa adapted to specific ranges of salinity. Finally, we investigated relationships among invertebrate biomass and sizes, sediment and hydrologic variables, and marsh types. Accordingly, we measured biomass of common invertebrate by three size classes (63 to 199 μm, 200 to 999 μm, and ≥1000 μm), sediment variables (carbon content, C:N ratio, hardness, particle size, and O2 penetration), and hydrologic variables (salinity, water depth, temperature, O2, and turbidity) in ponds of impounded freshwater (IF), oligohaline (IO), mesohaline (IM), and unimpounded mesohaline (UM) marshes during winters 1997–1998 to 1999–2000 on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana, USA. As predicted, ana priori multivariate analysis of variance (MANOVA) contrast indicated that biomass of an infaunal class of invertebrates (Nematoda, 63 to 199 μm) was greater in UM marsh ponds than in those of IM marshes, and biomass of an epifaunal class of invertebrates (Ostracoda, 200 to 999 μm) was greater in IM marsh ponds than in those of UM marshes. The observed reduction in Nematoda due to SMM also was consistent with the prediction that SMM reduces invertebrates that do not tolerate low salinity. Furthermore, as predicted, ana priori MANOVA contrast indicated that biomass of a single invertebrate class adapted to low salinity (Oligochaeta, 200 to 999 μm) was greater in ponds of IF marshes than in those of IO and IM marshes. A canonical correspondence analysis indicated that variation in salinity and O2 penetration best explained differences among sites that maximized biomass of the common invertebrate classes. Salinity was positively correlated with the silt-clay fraction, O2, and O2 penetration, and negatively correlated with water depth, sediment hardness, carbon, and C:N. Nematoda, Foraminifera, and Copepoda generally were associated with UM marsh ponds and high salinity, whereas other invertebrate classes were distributed among impounded marsh ponds and associated with lower salinity. Our results suggest that SMM and salinity have relatively small effects on invertebrate prey of wintering waterbirds in marsh ponds because they affect biomass of Nematoda and Oligochaeta, and few waterbirds consume these invertebrates.

Nesting success of common eiders Somateria mollissima as influenced by nest-site and female characteristics in the Gulf of the St. Lawrence

Abstract In the common eider Somateria mollissima as well as in many other bird species, nesting success has been associated with female reproductive characteristics and predator accessibility to the nest site. In this study, we tested the following predictions on nesting common eiders: 1) female and nest-site characteristics are correlated within a colony, where those with the highest ranked reproductive traits nest where the environment provides best protection, 2) females nesting on forested islands generally exhibit better reproductive traits than females nesting on open islets (hereafter habitats) because the former provide the best nest protection, and consequently, 3) colonies located on forested islands have higher nesting success than those on open islets. During the summers of 1995 and 1996, we recorded nesting success at 270 eider nests on two forested islands and four open islets. Simultaneously, we measured several variables describing nest (nest concealment, vegetation height, distance to shore and density of associated nesting gulls) and female (laying date and clutch size) characteristics. Using factor analysis to relate nest-site and female characteristics, we found a correlation between factor scores within four of the six colonies monitored. This correlation indicated that females with largest clutch size and early laying were associated with nest sites of low concealment that were close to shore. However, female score did not differ with habitat. Nesting success did not differ between habitats when controlled for female and nest scores, but was related to female score, and marginally to nest-site score. Because nesting success was principally related to female characteristics rather than to nest-site characteristics, we suggest that eiders rely on nest attendance rather than on nest concealment to protect their nests. Nesting close to shore may shorten incubation recesses and improve hatchling survival when leaving the nest.

Delineating Distance Intervals for Ship-based Seabird Surveys

Abstract. A system was developed for the delineation of distance intervals in front of an observer during seabird surveys. Delineation is based on a coordinates system (x.y) with the vanishing point on the horizon being the origin (0:0), within a vertical plane in front of the observer. Coordinates of parallel interval limits can be calculated using y = H x/dp (H = height of the observers eyes; dp = perpendicular distance between transect centerline and interval limit), and coordinates of radial interval limits using (wp = distance between the observer and the vertical plane in direction of interval limit; dc = observers distance to the interval limit). The use of the delineation system will help reduce observer-induced variation in seabird at-sea surveys.

Sediments in Marsh Ponds of the Gulf Coast Chenier Plain: Effects of Structural Marsh Management and Salinity

Physical characteristics of sediments in coastal marsh ponds (flooded zones of marsh associated with little vegetation) have important ecological consequences because they determine compositions of benthic invertebrate communities, which in turn influence compositions of waterbird communities. Sediments in marsh ponds of the Gulf Coast Chenier Plain potentially are affected by (1) structural marsh management (levees, water control structures and impoundments; SMM), and (2) variation in salinity. Based on available literature concerning effects of SMM on sediments in emergent plant zones (zones of marsh occasionally flooded and associated with dense vegetation) of coastal marshes, we predicted that SMM would increase sediment carbon content and sediment hardness, and decrease oxygen penetration (O2 depth) and the silt-clay fraction in marsh pond sediments. Assuming that freshwater marshes are more productive than are saline marshes, we also predicted that sediments of impounded freshwater marsh ponds would contain more carbon than those of impounded oligohaline and mesohaline marsh ponds, whereas C:N ratio, sediment hardness, silt-clay fraction, and O2 depth would be similar among pond types. Accordingly, we measured sediment variables within ponds of impounded and unimpounded marshes on Rockefeller State Wildlife Refuge, near Grand Chenier, Louisiana. To test the above predictions, we compared sediment variables (1) between ponds of impounded (IM) and unimpounded mesohaline marshes (UM), and (2) among ponds of impounded freshwater (IF), oligohaline (IO), and mesohaline (IM) marshes. An a priori multivariate analysis of variance (MANOVA) contrast indicated that sediments differed between IM and UM marsh ponds. As predicted, the silt-clay fraction and O2 depth were lower and carbon content, C:N ratio, and sediment hardness were higher in IM than in UM marsh ponds. An a priori MANOVA contrast also indicated that sediments differed among IF, IO, and IM marsh ponds. As predicted, carbon content was higher in IF marsh ponds than in ponds of other impounded marsh types. In contrast to our predictions, C:N ratio and sediment hardness were lowest and silt-clay fraction and O2 depth were highest in IO and IM marsh ponds. Our results indicated that SMM has affected physical properties of sediments in coastal marsh ponds. Moreover, sediments in IF marsh ponds were affected more so than were those in IO and IM marsh ponds. Our results, in conjunction with those of previous studies, indicated that sediments of marsh ponds and emergent plant zones differed greatly. We predict that changes in pond sediments due to SMM will promote greater epifaunal macroinvertebrate biomass, which in turn should attract larger populations of wintering waterbirds. However, waterbirds that filter or probe soft sediments may be negatively affected by SMM because of the expected decrease in infaunal invertebrate biomass.

Common Goldeneye Breeding in the Eastern Canadian Boreal Forest: Factors Affecting Productivity Estimates

Abstract We conducted multiple Common Goldeneye (Bucephala clangula) aerial surveys between 1 May and 31 July 2004 and 2005 on the Péribonka River, where a new hydroelectric reservoir will be created in 2007. We also conducted single pair and brood surveys on randomly chosen 5 × 5-km plots on the River drainage basin. Objectives were to assess the validity of the impact assessment surveys of 2002, examine the variation in pair and brood numbers, and determine recruitment and habitat characteristics related to productivity. During both years, the number of indicated breeding pairs (IBPs) declined steadily through May, whereas the social index (paired males/lone males) remained stable, declining only when few IBPs were located. However, backdated number of paired and lone males from observed broods suggested that the number of pairs remained maximal and constant during a three-week period centered on the fourth week of May in 2004 and the second week of May in 2005. IBP density (IBPs/10 km of shoreline) was 1.40 on the River and 0.64 in its drainage basin on average in 2005 (no surveys in 2004). When compared to results of the Black Duck Joint Venture (BDJV) surveys, IBP density was higher on the River by 0.69 IBPs in 2002, whereas densities in the two areas differed only by 0.07-0.29 in 2004 and 2005. No difference in brood density was perceived among survey sections and years. Recruitment rate was 0.15 in 2002, but increased to 0.57-0.67 in 2005 and 2004. Variables related to wetland area and distance to wetlands explained most variability in IBP and brood locations. We believe that timing of surveys and weather were the primary factors that affected difference in productivity estimates between 2002 and the 2004-2005 period.

Non-Breeding Distribution of Herring Gull (Larus argentatus) and Great Black-Backed Gull (Larus marinus) in Eastern Canada from Ship-Based Surveys

Abstract. Comprehensive understanding of the potential threats faced by seabirds requires information on their distribution and abundance in the marine environment where they spend a significant part of their life cycle. Data collected from shipboard seabird surveys from 2006–2014 were examined to identify high density marine areas in eastern Canada for Herring (Larus argentatus) and Great Black-backed (L. marinus) gulls during the nonbreeding season. The relative importance of these offshore areas was also compared to those used by Herring and Great Black-backed gulls in previous decades based on data collected from 1965–1992. Results show that both Herring and Great Black-backed gulls were broadly distributed over shelf waters throughout Atlantic Canada during the non-breeding season, as well as in the southern Gulf of St. Lawrence and the maritime St. Lawrence Estuary. These two species of gulls were also found to use the deeper slope waters, beyond the shelf break. The relative importance of different offshore areas for both species has changed over time, with decreases observed around the island of Newfoundland and on parts of the Scotian Shelf. An assessment of the overall vulnerability of Herring and Great Black-backed gull populations outside the breeding season will require continued monitoring at sea, integration of multiple datasets, and a comprehensive analysis of human activities offshore.