Reconnaissance of weathering rates in alpine catchments of central Colorado, USA
No abstract available.
Conference Paper↗
Geology topics
C. Bern
Publications and source records attributed to C. Bern.
Using stable isotopes to associate migratory shorebirds with their wintering locations in Argentina
We are evaluating the use of stable isotopes to identify the wintering areas of Neotropical migratory shorebirds in Argentina. Our goal is to associate individual birds, captured on the breeding grounds or in migration with specific winter sites, thereby helping to identify distinct areas used by different subpopulations. In January and February 2002 and 2003, we collected flight feathers from shorebirds at 23 wintering sites distributed across seven province s in Argentina (n = 170). Feathers samples were pre- pared and analyzed for δ 13 C, δ 15 N, δ 34 S, δ 18 O and δD by continuous flow methods. A discriminant function based on deuterium alone was not an accurate predictor of a shorebird’s province of origin, ranging from 8% correct (Santiago del Estero) to 80% correct (San ta Cruz). When other isotopes were included, the prediction accuracy increased substantially (from 56% in Buenos Aires to 100% in Tucumán). The improvement in accuracy was due to C/N, which separated D-depleted sites in the Andes from those in the south, and the inclusion of S separated sites with respect to their distance from the Atlantic. We also were able to correctly discriminate shorebirds from among two closely spaced sites within the province of Tierra del Fuego. These results suggest the feasibility of identifying the origin of a shorebird at a provincial level of accuracy, as well as uniquely identifying birds from some closely spaced sites. There is a high degree of intra- and inter-bird variability, especially in the Pampas region, where there is wide variety of wetland/water conditions. In that important shorebird region, the variability itself may in fact be the “signature.” Future addition of trace elements to the analyses may improve predictions based solely on stable isotopes.
Ornitologia Neotropical↗
Tracing the pathways of Neotropical migratory shorebirds using stable isotopes: A pilot study
We evaluated the potential use of stable isotopes to establish linkages between the wintering grounds and the breeding grounds of the Pectoral Sandpiper ( Calidris melanotos ), the White-rumped Sandpiper ( Calidris fuscicollis ), the Baird's Sandpiper ( Calidris bairdii ), and other Neotropical migratory shorebird species ( e.g. , Tringa spp.). These species molt their flight feathers on the wintering grounds and hence their flight feathers carry chemical signatures that are characteristic of their winter habitat. The objective of our pilot study was to assess the feasibility of identifying the winter origin of individual birds by: (1) collecting shorebird flight feathers from several widely separated Argentine sites and analyzing these for a suite of stable isotopes; and (2) analyzing the deuterium and 18 O isotope data that were available from precipitation measurement stations in Argentina. Isotopic ratios (δ 13 C, δ 15 N and δ 34 S) of flight feathers were significantly different among three widely separated sites in Argentina during January 2001. In terms of relative importance in separating the sites, δ 34 S was most important, followed by δ 15 N, and then δ 13 C. In the complete discriminant analysis, the classification function correctly predicted group membership in 85% of the cases (jackknifed classification matrix). In a stepwise analysis δ 13 C was dropped from the solution, and site membership was correctly predicted in 92% of cases (jackknifed matrix). Analysis of precipitation data showed that both δD and δ 18 O were significantly related to both latitude and longitude on a countrywide scale ( p < 0.001). Other variables, month , altitude , explained little additional variation in these isotope ratios. Several issues were identified that will likely constrain the degree of accuracy one can expect in predicting the geographic origin of birds from Argentina. There was unexplained variation in isotope ratios within and among the different wing feathers from individual birds. Such variation may indicate that birds are not faithful to a local site during their winter stay in Argentina. There was significant interannual variation in the δD and δ 18 O of precipitation. Hence, specific locations may not have a constant signature for some isotopes. Moreover, the fractionation that occurs in wetlands due to evaporation significantly skews local δD and δ 18 O values, which may undermine the strong large-scale gradients seen in the precipitation data. We are continuing the research with universities in Argentina with a focus on expanding the breadth of feather collection and attempting to resolve the identified issues.
Isotopes in Environmental and Health Studies↗