DIETARY EFFECTS ON PREDICTION OF BODY MASS CHANGES IN BIRDS BY PLASMA METABOLITES

Auk, The, Jul 2006 by Cerasale, David J, Guglielmo, Christopher G

ABSTRACT.-

Concentrations of plasma metabolites, including triglyceride, glycerol, and B-OH butyrate, can be used to determine refueling performance of migratory birds. We tested the effects of diet type and diet lipid content on the predictive relationships between metabolites and body mass changes in three species of passerines in captivity. In addition, we tested whether measurement of plasma phospholipids improved predictions of mass change. Rate of mass change was positively related to triglycerides in a captive frugivore (Cedar Waxwing; Bombycilla cedrorum) and a granivore (White-crowned Sparrow; Zonotrichia leucophrys). B-OH butyrate was negatively and nonlinearly related to mass change in Cedar Waxwings and White-crowned Sparrows. Glycerol was negatively related to mass change in Cedar Waxwings but not in White-crowned Sparrows. Mass change was positively related to triglycerides and negatively related to B-OH butyrate in Yellow-rumped Warblers (Dendroica coronata). There was no effect of diet lipid content (9% vs. 28% dry mass) on these predictive relationships. Plasma phospholipids were positively related to mass change in White-crowned Sparrows, but negatively related to mass change in Yellow-rumped Warblers and not related to mass change in Cedar Waxwings. Measurement of phospholipids did not improve prediction of mass change by metabolite profiles. Nevertheless, plasma metabolite profiles are predictive of short-term mass changes in captive birds regardless of diet type or diet lipid content, and can provide valuable information on refueling performance in studies of stopover ecology. Received 29 January 2005, accepted 16 October 2005.

Key words: bird, diet, lipid, mass change, migration, plasma metabolites.

Efectos de la Dieta sobre las Predicciones de los Cambios en el Peso Corporal de Aves por medio de Metabolitos Plasmáticos

RESUMEN.-Las concentraciones de metabolitos plasmáticos, como triglicéridos, glicerol y B-OH butirato, pueden ser usadas para determiner la capacidad de reabastecimiento de las aves migratorias. Probamos el efecto del tipo de dieta y del contenido de lipidos sobre la relación de predicción entre los metabolitos y los cambios en el peso corporal en tres especies de aves paserinas en cautiverio. Además, probamos si la medición de fosfolápidos plasmáticos mejoraba la predicción de los cambios en el peso corporal. La tasa de cambio del peso se relacionó positivamente con los triglicéridos en un frugávore (Bombycilla cedrorum) y en un granivore (Zonotrichia leucophrys). El B-OH butirato se correlacionó negativamente y de forma no lineal con el cambio en el peso de B. cedrorum y Z. leucophrys. El glicerol se relacionó negativamente con el cambio del peso en B. cedrorum, pero no en Z. leucophrys. En Dendroica coronata, el cambio del peso se relacionó positivamente con los triglicéridos y negativamente con el B-OH butirato. No hubo un efecto del contenido de lípidos en la dieta (9% vs. 28% de peso seco) sobre estas relaciones de predicción. Los fosfolípidos plasmáticos se relacionaron positivamente con el cambio del peso en Z. leucophrys, se relacionaron negativamente con el cambio del peso en D. coronata, y no se relacionaron con el cambio del peso en B. cedrorum. La medición de fosfolápidos no mejoró la predicción de los cambios del peso mediante perfiles de metabolitos. Sin embargo, los perfiles de metabolitos plasmáticos pueden predecir los cambios en el peso a corto plazo independientemente del tipo de dieta o del contenido de lípidos en aves en cautiverio, y pueden proveer información importante sobre la capacidad de reabastecimiento en estudios sobre ecología migratoria.

MANY AVIAN MIGRANTS traverse thousands of kilometers between breeding and wintering areas. Most birds cannot complete their journey in a single endurance flight and must stop to replenish energy stores. Theoretical models predict that refueling rate during stopover is a major determinant of migration success and, thus, can affect overall survival and reproduction (Alerstam and Lindström 1990, Alerstam and Hedenström 1998, Weber et al. 1998). Migrants that replenish energy stores quickly during stopover will minimize total time spent migrating, increase the probability of early arrival on breeding or wintering grounds, and decrease time spent in unfamiliar territory (Alerstam and Lindström 1990, Lindström and Alerstam 1992). Weber et al. (1998) contend that refueling rate is an effective measure of stopover habitat quality. Measurement of refueling rate in free-living birds, however, has proved difficult. Techniques commonly used to estimate mass change, such as recapture analysis (e.g., Moore and Kerlinger 1987, Schaub and Jenni 2000) and mass-versus-time-of-day regression (e.g., Winker et al. 1992, Yong et al. 1998), often require large sampling efforts and have associated capture biases (Guglielmo et al. 2005). Recently, plasma metabolite profiling has received attention as a physiological technique to measure body mass change in free-living birds while avoiding some of the shortcomings of traditional methods (e.g., Schaub and Jenni 2001; Guglielmo et al. 2002a, 2005; Ydenberg et al. 2002).