Fine-scale foraging behavior of bison in nutritionally heterogeneous grasslands in response to fire and drought

Background/Question/Methods

Foraging behavior of native grazers in fire dependent landscapes is an integral component of the fire-grazing interaction. The behavioral mechanism behind the attraction of grazers to recently burned areas requires understanding at each of three spatial scales of the ecological hierarchy of foraging:  especially the feeding station responses (area between steps in a foraging bout ), which drives foraging decisions at the next level in the foraging hierarchy. In this study, we relate the tradeoff between forage quantity and quality to foraging decisions at the feeding station scale in grasslands with varying burn history at Konza Prairie Biological Station.

Results/Conclusions

Bite mass increased linearly with increasing feeding station biomass, while bite rate declined. Food intake rate was influenced primarily by bite mass and thus increased linearly with grass biomass. At sites burned in the spring just prior to focal animal observation after many years of no burning, intake rate increased with increasing biomass at a greater rate during the growing season than in the transitional period of mid- summer, indicating bison were consuming this highly nutritional resource despite potential ingestive constraints. Instantaneous intake rate did not vary by season in frequently burned grassland or at sites that were not burned the preceding spring. Periodic fire is an important component of grazer foraging behavior with strong influence on feeding station level foraging decisions. In addition, bison compensate for the availability of low forage quality by adjusting bite mass and intake rate during the dormant season. Our findings document the behavioral dynamics of bison foraging at the smallest scale when faced with forage that varies in quality and quantity in nutritionally heterogeneous grasslands.