Geology topics

Eric J. Smith

Publications and source records attributed to Eric J. Smith.

2 recordsLinked to original sources

USGS2023

Lipid metabolites index habitat quality for Canvasbacks on stopover areas during spring migration

Nutrients acquired by ducks on spring migratory stopover areas influence survival and subsequent reproduction. Accordingly, wetland loss and degradation on stopover areas can lead to reduced refueling efficiency and have demographic consequences. Lipid metabolite concentrations in blood provide a useful index of daily mass change in wild birds and can be used to make inferences about quality of stopover areas for refueling. We experimentally validated a model that uses lipid metabolites to predict daily mass change, and then we used those predictions to make inferences about foraging habitat quality for Canvasbacks ( Aythya valisineria ) at important stopover sites of the upper Mississippi and Illinois Rivers, USA. We measured plasma lipid metabolites and daily mass change of 60 wild Canvasbacks held in short-term captivity and subjected to feeding and fasting treatments. Respectively, triglyceride and β-hydroxybutyrate concentrations were positively and negatively related to mass change ( R 2 = 0.58). On average, Canvasbacks collected experimentally across our study area had positive index values indicating sufficient forage resources to allow energy acquisition. However, predicted daily mass increases were greater at more northerly pools of the Mississippi River (Pools 7–8 and 13) compared to more southerly locations (Pool 19 of the Mississippi River and the Illinois River Valley), which was likely due, in part, to more abundant submerged aquatic vegetation at more northerly pools. Our results affirm that lipid metabolites are useful predictors of daily mass change that in turn can provide inferences about habitat quality. Lower daily mass increases of Canvasbacks at Pool 19 are concerning because that area is considered a critically important spring stopover area for migratory diving ducks. Considering the challenges of managing large rivers for multiple uses, targeting restoration of wetlands isolated or isolatable from river systems could provide stopover areas with necessary forage for optimal mass gain.

Illinois, Wisconsin↗

USGS2021

Plasma metabolite indices are robust to extrinsic variation and useful indicators of foraging habitat quality in Lesser Scaup

Energy acquisition and storage are important for survival and fecundity of birds during resource-limited periods such as spring migration. Plasma-lipid metabolites (i.e. triglyceride [TRIG], β-hydroxybutyrate [BOHB]) have been used to index changes in lipid stores and, thus, have utility for assessing foraging habitat quality during migration. However, such an index may be affected by energetic maintenance costs, diet, and other factors, and further validation under experimental conditions is needed to understand potential sources of variation and verify existing indices. We evaluated a plasma-lipid metabolite index using 30 female and 28 male wild Lesser Scaup ( Aythya affinis ; hereafter scaup) held in short-term captivity (~24 hr) during spring migration. Similar to previous observational studies, BOHB was negatively associated and TRIG was positively associated with mass change ( R 2 = 0.68). BOHB estimates were nearly identical to those published on free-living scaup, but TRIG estimates differed from free-living scaup and varied by sex, with females having a greater rate of predicted mass change than captive and free-living males. Our results suggest TRIG may be a better measure of energy income than deposition because lipid deposition likely varies with energetic maintenance costs, stress, and underlying physiological processes while TRIG relates primarily to energy income. In contrast, BOHB was a reliable predictor of negative mass change across sexes. The sex-based differences in apparent lipid deposition rates warrant further research before a generalizable model is advisable for comparing mass change predictions across studies. However, if predictions are standardized, this technique is generally robust to variations in energy income vs. lipid deposition across sexes. Accordingly, our evaluation provides verification for the utility of plasma-lipid metabolites as an indicator of foraging habitat quality during migration.

Illinois↗