Natal dispersal and natural history of the Virginia opossum (Didelphis virginiana) in two midwestern populations

Despite the abundance of the Virginia opossum (Didelphis virginiana ), there have been relatively few studies on its movement patterns. I examined: (1) juvenile opossum dispersal, (2) opossum natural history and demography, and (3) opossum abundance and spatial distribution. Study sites were located in two different study areas: cultivated lands in Madison County, Illinois, and a natural, contiguous, forested area in St. Louis County, Missouri. I live-trapped a total of 39 opossums (including juveniles and adults) as a result of 1428 trap nights in both study areas combined from January 2001 to April 2002. I conducted an investigation on 12 juvenile opossums using radio-transmitters, GPS, and GIS to determine their natal dispersal distance and movement patterns.; Results were evaluated with regards to: (1) the competition avoidance hypothesis that suggests that resource competition between parents and offspring cause offspring to leave the natal area; and (2) the inbreeding avoidance hypothesis that suggests that emigration before age of sexual maturity would tend to decrease chances of inbreeding.; Juvenile opossums experienced 0% mortality within the first 4 weeks after transmitter implantation. Of all juveniles ear-notched, 92% survived until their first breeding season and 87% of the total sample were alive at the conclusion of the study. Female dispersal distance is known since 5 of the 7 radio-tagged females successfully reproduced and 2 other radio-tagged females were located (without pouch young) during the breeding season. None of ear-notched males were found to have reproduced in the study area since all dispersed before breeding season.; All males (100%) dispersed from the natal area, while most females remained in the natal area (86%). The latter percentage includes one female that died in the study area. No significant difference in opossum natal dispersal distance, home range size, density, and sex ratio were found between study areas. Sexually dimorphic dispersal patterns were statistically significant. Males dispersed a mean minimum distance of 747 m and females an average of 244 m from natal area to first breeding site. No significant differences were found in home range size between the sexes. However, because males exhibited a different pattern of movement than females, it is not entirely certain that space use by juvenile/subadult male opossums can be defined as true home ranges during the period of dispersal in this study. Sex ratio was approximately even within study areas.; In conclusion, juvenile/subadult male opossums dispersed significantly longer distances than juvenile/subadult females as was predicted. Data did not support the predictions regarding differences in home range size, dispersal distance, and density between study areas. Dispersal of opossums in my study areas may be driven by density related pressures. A secondary effect of this behavior may be inbreeding avoidance.