Body fat levels of northern bobwhites in south Texas

Adult northern bobwhites (Colinus virginianus) (N = 671) were collected from 5 counties in south Texas during January 1982-November 1983 to determine percentage body fat. Mean body fat levels of females exceeded (P 0.05) in autumn and winter. For both males and females (samples from areas pooled), mean percentage body fat decreased from winter to spring, increased from spring to summer, decreased from summer to autumn, and increased from autumn to winter. However, in 2 counties for females and 1 for males, mean body fat did not vary seasonally (P > 0.05). J. WILDL. MANAGE. 51(1):194-197 Because levels of body fat reflect the health and nutritional status of wildlife populations and the quality of habitats (Kirkpatrick 1980:106109), they can be used to index population and habitat status. However, normal levels must be established for specific regions, because fat deposition in a given species tends to be higher in cooler than in warmer climates (Blem 1976). For this reason, published information on percentage body fat in northern bobwhites (Robel 1969, 1972; Robel et al. 1974; Dabney and Dimmick 1977; Warren et al., 1984) may not apply to birds in more southerly latitudes. Therefore, we determined fat levels for adult bobwhites in south Texas and examined factors that affected these levels. We thank L. J. Welder, C. K. McCan, C. Linecum, J. M. Benavides, R. Eads, and H. A. Fitzsimmons, Jr., for access to study areas and the Caesar Kleberg Found. for Wildl. Conserv. for funding the study. T. E. Fulbright, R. A. Bingham, R. D. Brown, and J. H. Rappole reviewed the manuscript. STUDY AREAS AND METHODS One study area >880 ha was selected in each of 5 counties (Refugio, Brooks, Duval, Webb, and Dimmit) in the South Texas Plains (Fig. 1). Average annual precipitation approaches 90 cm in Refugio County and ranges between 50 and 60 cm in other counties. Dominant soils are heavy clays on the Refugio County area, deep sands on the Brooks County area, and sandy loams on other areas. Gould (1975) described the regional environment and Koerth (1985) gave more detail on study areas. Birds on all areas had access to corn and sorghum during portions of autumn and winter. Availability ranged from intermittent scattering f grain by out-of-state hunters during November-January to routine provision of grain at fixed feeders. Adult bobwhites (283 females and 388 males) were collected monthly from each area during January 1982-November 1983 (Table 1). Young of the previous year were considered adults on 1 March. Crops were removed and birds were ground while frozen, dried at 70 C for 48 hours, and reground finely in a Wiley mill. Crude fat w s extracted from duplicate 1.5-g samples with ether for 8 hours in a Goldfisch apparatus (modification of Harris [1970:230]). If duplicates differed by >10%, additional duplicates were analyzed and the mean value of duplicates differing by < 10% was used in analysis. Percentage body fat (dry-matter basis) was calculated as (sample fat wt/sample wt) x 100. The effect of sex on mean percentage body fat was tested by analysis of variance (ANOVA) within areas and seasons, because of an interaction effect (P = 0.0096) of area and season. The Mann-Whitney U-test was used to distinguish differences in mean fat between sexes. The effect of season on mean percentage body fat was determined within areas using 1-way ANOVA. Tukey's Honestly Significant Difference test was used to distinguish differences between seasons, except in 4 cases when it failed to separate means even though the ANOVA indicated seasonal effects. In these cases, Fisher's Least Significant Difference test was used. ANOVA and multiple comparison tests were done on rank-transformed data, resulting in nonparametric tests (Conover and Iman 1981). Seasons were winter (Dec-Feb), spring (Mar-May), summer (Jun-Aug), and autumn (Sep-Nov).