Bison (Bison bison) dung Decays Slowly but Can Still be Used to Track Short- and Long-Term Habitat Usage

Dung counts can be a cheap and effective way to estimate herbivore density across grassland and savanna ecosystems. However, estimating animal density requires information on the decay rate of dung and the animal's defecation rate. Before the arrival of Europeans, the American Bison (Bison bison) was one of the most widespread megafauna in North America. Yet, we are unaware of any study that has quantified the fundamental measurements of dung decay and deposition rates in bison. This study aimed to determine the dung decay rate and defecation rate of bison to estimate population size and habitat usage. The decay rate of bison dung was tracked by revisiting cohorts of dung piles throughout the year for an average of 184 days using a five-class classification system to track the decay process. Only 23 of our 78 dung piles fully decayed within the 168 to 211 days of tracking, with an average of 101 days for decay, which is substantially slower than similar megafauna, such as cattle and cape buffalo. However, using a decay class system instead of full decay is useful in tracking bison habitat usage because dung transitions to class 4 over a consistent 25 to 30 days. Based on video recordings in autumn, the average defecation rate of bison was calculated to be approximately 10.7 dung piles per animal per day. These results can be used to track bison habitat usage in grassland ecosystems, with especially high accuracy of usage in the last 30 days.