Long-term population trends of raccoons in Illinois

Abstract

While knowledge of population trends is critical to the evaluation of management efforts involving raccoons (Procyon lotor), long-term data on population abundance at a large spatial scale are lacking for this species. The Illinois Department of Natural Resources has been conducting statewide road-kill surveys since 1975 and spotlight surveys since 1981. Trends of seasonal road-kill indices (RKls) were highly (P<0.001) correlated to each other. Annual adjusted RKls (RKl a d j ) and spotlight indices (SIs) consistently increased during a 5-year period between 1989 and 1993, and maintained a high level during the 1990s. Annual RKl a d j and Sls were positively correlated (r=0.96, n=17, P< 0.001) at lag 0 (i.e., same year). Annual harvest estimates had a negative trend and were highly correlated (r=0.86, n=23, P≤0.001) with pelt values. Cross-correlation analysis with harvest (t-1) was significant for annual RKI a d j (r=-0.71, n=22, P≤0.001), breeding RKl a d j (r=-0.69, n=22, P≤0.001), and SI (r=-0.65, n=17, P=0.005). The concordance between road-kill and spotlight data, despite marked differences in methodology and influential variables between the techniques, suggests that both types of surveys may be valid for determining relative changes in raccoon abundance at a statewide scale, particularly over multiple years. Thus, it appears the raccoon population in Illinois experienced an increase in abundance during a period of low pelt prices and harvest levels.