Demographics and Condition of Coyotes in Illinois
Nelson, Thomas A., Lloyd, Daniel M., The American Midland Naturalist
The rapid growth of coyote (Canis latrans) populations in Illinois since 1980 prompted a need for current demographic data to be used in population models for management. From 1994 to 1997 we examined 977 coyotes harvested by hunters and trappers throughout the state and compiled data on age structure, sex ratios, reproductive rates and physical condition. Statewide, 55% of harvested coyotes were juveniles, 20% were yearlings and 25% adults. The sex ratio did not differ from unity among juveniles and yearlings, but was skewed towards males in the adult class. The number of harvested animals decreased by 45-60% between successive classes from 0.5 through 2.5 y old, then by 30-40% through 9.5 y old. Statewide, 57% of females bred and breeders averaged 4.9 placental scars. Males were larger than females, averaging 14.1 and 12.1 kg whole body mass, respectively. Kidney fat reserves were highest in juveniles and adult females and lowest in yearlings. Femur marrow fat was generally high and did not differ among age-classes. Ovulating females were heavier than non-ovulators among juveniles and yearlings. We found that coyotes in Illinois are in good physical condition with high winter fat reserves and reproductive rates. However, reproductive rates are lower than they were in 1978-1979 when the population was rapidly expanding in the state.
Knowledge of coyote (Canis latrans) ecology and demographics is important because they are the largest native predator in most of the eastern U.S., provide recreation and economic opportunities for hunters and trappers and can be a nuisance species. Consequently, a large body of scientific research has accumulated on the species' ecology, behavior and demographics (Gier, 1968; Knowlton, 1972; Bekoff, 1982; Andelt, 1985).
In Illinois, coyote densities were low through the 1960s and until 1973 there was no state statute regarding their harvest. However, during the 1970s the population began to grow rapidly in the state. In the mid-1970s about 3000 coyotes were harvested annually, but by the 1980s annual harvests exceeded 10,000 and the resident population was estimated at 20,000-30,000 (Hoffmeister, 1989). Increasing harvests and nuisance complaints prompted the Illinois Department of Natural Resources (IDNR) to develop population models to aid in coyote management. However, limited demographic analyses were available for coyotes in the midwestern U.S. and none for Illinois. We conducted this study to provide these data. Our objectives were to: (1) estimate the age-structures and sex ratios of harvested coyotes in Illinois, (2) assess age-specific reproductive rates and (3) evaluate the relationships among age, physical condition and reproductive rates of female coyotes in Illinois.
Coyote carcasses were collected from December to March each year from 1994 to 1997. Fur buyers and hunters throughout Illinois provided carcasses. For each coyote, we recorded the county, date, method of harvest, sex, body length (tip of nose to tip of tail) and skinned body mass. We extracted lower canines for aging. Teeth were initially x-rayed to separate juveniles from adults based on the width of the pulp cavity (Kuehn and Berg, 1983). Teeth from adults were sent to Matson's Laboratory (Milltown, MT) where age was estimated using cementum annuli (Linhart and Knowlton, 1967). In Illinois, most coyotes are born in April (Hoffmeister, 1989). Consequently, the juveniles in our sample were 8-11 mo old, yearlings were 20-23 mo old and adults were >32 mo of age.
The physical condition of each coyote was estimated by measuring three indices of body fat: kidney fat index (KFI; Riney, 1955), femur marrow fat (FMF; Huot et al., 1995) and kidney-femur fat index (KFFI). We dried FMF samples, weighed them to the nearest 0.1 mg and the lipids were extracted using petroleum ether and a Soxhlet apparatus (Sawicka-Kapusta. 1975; Dobush et al. …