A Preliminary Body Fat Index for Cottontails 
(Lagomorpha: Leporidae) 
Edward M. Lunk 
Department of Forestry, North Carolina State University, 
Raleigh, North Carolina 27695 
ABSTRACT — Total body fat is frequently used as an indicator of 
an animal’s physical condition, but its determination requires post- 
mortem analysis. A field index of total body fat useful on live 
cottontails ( Sylvilagus floridanus ) was developed. I collected a small 
sample of cottontails in April 1984 to determine total body fat. 
Carcasses were homogenized and assayed for ether extraction of 
crude fat. A significant regression equation predicting the natural 
log of crude fat expressed as a percentage of dry mass from the 
natural log of the mass/head-length was developed. 
An animal’s plane of physical condition is considered directly 
related to the abundance and quality of life’s necessities in the 
habitat, which ultimately affect population productivity (Martin 1977). 
Body fat reserves are commonly used to indicate an animal’s physi- 
cal condition, which in turn, can be used to infer habitat quality or 
rate of population increase (Caughley 1970, Martin 1977). I had 
particular interest in determining the feasibility of developing a quick 
field index of body condition for use in mark-recapture, radio te- 
lemetry, and other investigations of live eastern cottontails. 
In previous studies, Havera (1977) found that total percentage 
of carcass fat was the best indicator of the condition of fox squir- 
rels ( Sciurus niger), and Robel et al. (1974) found that total car- 
cass fat was related to food quality in northern bobwhite ( Colinus 
virginianus). 
Indices of fat content are often practical surrogates for the 
much more costly laboratory determinations of total body fat. Fin- 
ger et al. (1981) used a kidney fat index, which proved to be 
correlated with total body fat of white-tailed deer ( Odocoileus 
virginianus). Bamford (1970) found significant correlation between 
both abdominal and kidney fat indices and total body fat. Riney 
(1955) developed a kidney fat index, and combined fat measures 
have been used by Anderson et al. (1969, 1972). Martin (1977) 
used an abdominal fat index for indicating fat reserves in European 
wild rabbits ( Oryctolagus cuniculus). Bamford (1970) found a sig- 
nificant relationship between a length:standardized-mass ratio and to- 
tal body fat in the brush-tailed possum (Trichosurus vulpecula). Bailey 
(1968) reported on the use of mass/length (nose tip to tip of fur 
on fully extended hind feet) as an index of physical condition in 
Brimleyana 19:141-145, December 1993 141 
