Evaluation of Lipid Indices of the Wood Thrush

Abstract

Many techniques for assessing lipid reserves have been used, but techniques are seldom evaluated. We evaluated five common methods (fat scoring, regression residuals of body mass vs. morphological measurements, quotients of body mass divided by morphological measurements, total body electrical conductivity, and water content) for assessing lipid reserves in the Wood Thrush (Hylocichla mustelina) in Rhode Island. Lipid content ranged from 3 to 1 l%, water content ranged from 64 to 72%, and fat score ranged from 0 to 4. Mean total body electrical conductivity (TOBEC) was moderately correlated with lean body mass. Percentage water and fat score were highly correlated with extracted lipid mass and percentage lipid content. Body mass, tail x mass regression residuals, and quotient of body mass/tail length were highly correlated with lean body mass. Morphological measurements were correlated with lean mass only when in association with body mass, but not considered alone. Combining TOBEC readings with body mass and morphological measurements produced regression models with similar predictive abilities as previous studies using TOBEC, but TOBEC provided little or no additional predictive ability. TOBEC did not significantly improve body fat predictive models and does not appear accurate in predicting lipid mass of individual small birds. Fat score and percentage water are useful indices of body fat in Wood Thrush.

Estimation of Carcass Fat and Protein in Northern Pintails (Anas Acuta) During Spring Migration

“…In other studies, body mass was a fair predictor of carcass fat (Miller, 1989 [r 2 ϭ0.63]; Smith et al, 1992 [r 2 ϭ0.69-0.74]) and carcass protein (Miller, 1989 [r 2 ϭ0.71]). However, carcass fat was estimated more precisely by percent water (Miller, 1989 [r 2 ϭ0.92-0.95]; Conway et al, 1994 [r 2 ϭ0.86]).…”

“…Because of this, easier and less expensive methods have been developed to estimate body nutrient reserves. These methods involve equations or indices based on: 1) morphometric measurements including body mass (Johnson et al, 1985;Ringelman and Szymczak, 1985;Miller, 1989;Smith et al, 1992;Dabbert et al, 1997); 2) amounts of fat and protein in different tissues (Chappell and Titman, 1983;Whyte and Bolen, 1984;Johnson et al, 1985;Hohman and Taylor, 1986;Miller, 1989;Smith et al, 1992;Dabbert et al, 1997); or 3) water content of the carcass (Child and Marshall, 1970;Campbell and Leatherland, 1980;Johnson et al, 1985;Miller, 1989;Conway et al, 1994;Karasov and Pinshow, 1998). For example, body mass was found to be a good predictor of nutrient reserves in northern pintails from Texas (Smith et al, 1992) and California (Miller, 1989).…”

Evaluation of the TOBEC Method for Calculating Fat Mass in Tree SparrowsPasser montanusand House SparrowsPasser domesticus

“…They then took the mean of the total of 100 readings. Conway et al (1994), working on the Wood Thrush Hylocichla mustelina, repeated TOBEC measurements 16 times, and recommended that an average of 9 measurements be made. Roby et al (1997), and Zuercher et al (1997), applied 6 repetitions of TOBEC measurements, while Burger (1997) used 7 measurements per bird.…”

“…However, because it allowed for estimates of amounts of fat in live vertebrates, it soon found application in scientific research on: human adult males (Presta et al 1983a, b) and infants (Cochran et al 1989), pigs (Fiorotto et al 1987, Cochran et al 1989), rabbits (Fiorotto et al 1987), rodents (Bracco et al 1983, Piasecki et al 1995, Koteja 1996, Zuercher et al 1997, fish (Fisher et al 1996) and birds (Walsberg 1988, Castro et al 1990, Morton et al 1991, Roby 1991, Scott et al 1991, Skagen et al 1993, Conway et al 1994, Asch & Roby 1995, Lyons & Haig 1995, Staudinger et al 1995, Burger 1997.…”

“…In animals with small amounts of fat these errors may reach 200% of real fat mass (Skagen et al 1993, Conway et al 1994, Zuercher et al 1997. However, in such cases it is possible to make intraspecific comparisons using the TOBECestimated mean fat mass of an appropriately-large group of animals, especially where individuals in these groups do not differ in mean body mass.…”