Geology topics
P.L. Leberg
Publications and source records attributed to P.L. Leberg.
Lipid and water depletion in migrating passerines following passage over the Gulf of Mexico
Lipid depletion is currently believed to be the primary factor limiting flight duration of migrating birds in North America, while the influence of water loss is thought to be small. Three migrating species of passerines, wood thrush ( Hylocichla mustelina ), Swainson's thrush ( Catharus ustulatus ), and summer tanager ( Piranga rubra ) were captured during the 1993 spring migration just after crossing the Gulf of Mexico and examined for lipid and water depletion. The redwinged blackbird ( Agelaius phoeniceus ), a winter resident, was examined for comparison. Although some migrants had low levels of fat, most were not seriously fat-depleted and had much higher lipid levels than red-winged blackbirds. Migrants appeared dehydrated, usually having less than 60% body water and significantly less water than the blackbirds. Recaptured wood thrushes had significantly higher mass than when initially captured. Many of these birds were replenishing significant amounts of water, while the acquisition of lipid mass was dependent on the amount of time the birds spent on the study site. Migrants were significantly fatter but had significantly less water mass when captured during unfavorable weather than under favorable conditions. It appears that both dehydration and lipid depletion are major physiological constraints on migrating passerines.
Comparison of condition indices in migratory passerines at a stopover site in coastal Louisiana
We evaluated the utility of four nondestructive condition indices—body mass, body mass scaled by wing chord length, fat scoring, and total body electrical conductivity method (TOBEC)—as predictors of lipid levels in migrating Wood Thrushes ( Hylocichla mustelina ), Swainson's Thrushes ( Catharus ustulatus ), and Summer Tanagers ( Piranga rubra ). The Red-winged Blackbird ( Agelaius phoeniceus ), a winter resident, was examined for comparative purposes. In addition, we examined differences among species in relationships of total body lipids and condition indices. Body mass was the best index of lipid levels, explaining 36%-82% of the variation in total body lipids in all four species. The relative contributions of the other indices to the prediction of lipid mass varied among species although TOBEC was selected for inclusion in each regression equation. For two species, equations including TOBEC measurements had lower errors in lipid prediction than equations only using the other nondestructive indices. Errors in lipid prediction were large for all the regression equations based on condition indices. In many cases it will be necessary to develop species-specific equations to predict lipid levels with condition indices.