Indirect Effects of Elk Harvesting on Ravens in Jackson Hole, Wyoming

Harvesting of marine and terrestrial animals by humans produces animal biomass byproducts that many scavenger species exploit. Effects of food byproducts from harvesting on the ecology of scavenger species has rarely been measured, especially in terrestrial systems. Such nutritional subsidization of scavengers needs to be monitored because increases in their populations may influence population dynamics of other species and alter natural community dynamics. I quantified effects of the distribution of elk (Cervus elaphus) gutpiles generated by an intensive harvest program in Jackson Hole, Wyoming, USA, on local raven (Corvus corax) foraging behaviors, daily and seasonal movements, and population distribution. During Jackson Hole's 2001 fall elk harvest, I found ravens to be the most abundant vertebrate species scavenging on monitored gutpiles, and the number of ravens I detected during fixed-width transect surveys positively correlated with concurrent, sympatric gutpile densities. I found raven abundance, estimated via point-count surveys in habitat-paired harvest zone and reference plots, to increase significantly in conjunction with the fall elk harvest only in the harvest zone plots. Furthermore, estimated raven abundance and nest density in the spring were significantly higher in the harvest zone plots than in the reference plots. Results indicate that in Jackson Hole, ravens exploit gutpiles provided by elk harvesting, daily raven distribution in the fall corresponds with the immediate distribution of gutpiles across the landscape, fall raven abundance is associated with the overall density of gutpiles in a given area in the fall, and spring raven abundance and nest density are associated with fall gutpile density. Collectively, these findings suggest that the high concentration of elk gutpiles in Jackson Hole is a significant supplemental food resource for ravens, and that wildlife harvesting in a terrestrial environment is capable of influencing the foraging behaviors, movements, and population dynamics of scavenger species. Wildlife managers must consider nontarget species when evaluating the efficacy of their regulatory programs and work to minimize unintended effects caused by wildlife management on the surrounding ecological community. Jackson Hole's elk population regulation program is a model for ungulate management due to its long-term success, while at the same time managers in Jackson Hole are continually addressing how their program may affect the surrounding ecological community and considering alternative management strategies to more effectively conserve the region's diversity. Results here provide baseline information on raven ecology in relation to Jackson Hole's current elk management program for comparison to other areas with intensive ungulate management programs, and for later comparison within Jackson Hole as strategies for managing its elk population change in the future. This study also draws attention toward monitoring effects of anthropogenic byproduct food resources that, despite their inconspicuousness in the literature, can substantially influence the ecology of opportunistic scavengers; and it points out several scavenger species other than ravens that also may be influenced by access to gutpiles or other anthropogenic foods that are abundant, reliable, and nutritious. Finally, having determined a clear link between elk harvesting and the population dynamics of ravens—an influential species in its ecological community—this study sets the stage for future research, testing the strength and extent of a trophic cascade that may be initiated by gutpile availability and propagated by increases in raven population density in Jackson Hole.