Population ecology of badgers (Taxidea taxus) in Ohio
Jared F. Duquette, MS
Advisor: Stan Gehrt
There is a paucity of information concerning American badger (Taxidea taxus) ecology across the geographic range of this mesocarnivore. Virtually no research has addressed the ecology of the badger east of the Mississippi River, particularly in a highly fragmented agricultural landscape typical of this region. Therefore, I conducted a study to assess certain aspects of badger ecology in areas dominated by agricultural use in Ohio and west central Illinois.
I evaluated the state-wide badger distribution in Ohio through the collection of badger observations using a state-wide publicity campaign. Overall, 387 badger observations were collected: unconfirmed reports were most numerous (43%), followed by probable (32%), and confirmed (25%). Relatively few observations were recorded until the early 1990’s when they began to increase, and sharply increased during the 3-year study period. Badgers were recorded in 56 counties, but most (>99%) of observations were found in 53 counties above the glacial line.
I determined multi-scale spatial ecology and habitat use using radiotelemetry data for badgers in Ohio (n = 5) and Illinois (n = 14) and an independent set of badger observations in Ohio. Mean 95% FK annual home ranges in Illinois were larger than in Ohio, but mean 50% FK annual home ranges did not differ between states. Mean 95% FK annual home ranges for males were larger in Illinois than in Ohio; however, male 50% FK and both female annual home ranges did not differ between states. Both male home range sizes did not differ from females in Ohio, but 95% and 50% FK were larger for males than females in Illinois over annual periods and during the rearing season; the 95% FK was also larger for males than females in Illinois during the breeding season. Badgers in both states selected agricultural habitat within their home ranges, and linear grassland and wetland-associated habitats within the study area landscape. Ohio badger observations showed badger occurrence was associated with interspersed blocks of agriculture and linear grassland habitats.
The spatially explicit habitat-relative abundance of badgers in Ohio was determined through an independent set of badger observations and core home range habitat use. Badger occurrence was associated with interspersed small blocks of agriculture and linear grassland habitats. The model determined that 51% of the state contained likely badger occurrence, 13% intermediate occurrence, and 36% unlikely occurrence. The greatest likelihood of occurrence was mainly in the northwest, southwest, and north central regions of the state. Predicted relative abundance was relatively uniform in the northwest and north central regions of the state, with a uniform pocket of likely occurrence in the south central region. The remainder of the state was interspersed with likely to unlikely badger occurrence.
I evaluated population demography and diet through the collection and necropsy of badger carcasses (n = 46) from 2005 to 2008. Diet data from 25 badgers showed small mammals were predominately the main prey items. Mean age of 38 badgers was 1.63 years and categorically consisted of 34% young-of-year, 16% sub-adults, and 50% adults. Fecundity was estimated as 0.302 with a mean litter size of 2.17 and 31.6% occurrence of parous females, which included 2 known age young-of-year. The base population model with a starting population of 500 females increased (λ = 1.032) gradually after 20 years. Badger young-of-year survival appeared to be an important factor for influencing population growth rate, as lower estimates caused substantial population declines over a 20-year time period. A simulated 4.5% population harvest also showed sharp population declines over the same period.
Deforestation and agricultural practices have likely allowed the population expansion of badgers into areas of the state beyond the historical distribution that was presumably restricted to prairie pockets of the state. The spatial ecology of badgers in agricultural landscapes appears to be contingent on the habitat composition in the respective landscape. Badgers use the landscape at multiple spatial scales and management of grassland habitats and riparian corridors appear to be important to the conservation of this species. In addition, the future trend of this low-density population is highly dependent on the survival and reproduction of female badgers, particularly younger animals.