Interactions between hare and brent goose in a salt marsh system; evidence for food competition?

Abstract

In this study we accumulate evidence that brown hare competes with brent goose for food resources in a temperate salt marsh. We show that both species overlap in habitat use and share food plants. The two herbivores mainly used the common habitat at different times of the day, with hares active in the dark and geese during the daylight. During the morning and evening, however, the habitat was exploited simultaneously. Food availability was manipulated by excluding brent geese on both small-scale (30 m2) and large-scale (0.96 ha) plots, while hares had free access everywhere. Exclusion of brent geese enhanced the level of utilisation by hares in both Festuca and Puccinellia dominated marshes, which are among the most intensively grazed parts of the salt marsh. The increase in hare grazing pressure following goose exclusion was stronger, when the adjacent control plots had attracted more goose visitation. When geese were excluded, the decrease in Festuca consumption by geese was completely matched by increased hare grazing, while for Puccinellia only part of the `surplus' was harvested. Enhanced levels of hare utilisation were not due to geese interfering directly with hare, nor due to hares avoiding goose droppings. Considering the interaction from the other perspective, hares were observed to disturb geese effectively in every spring. This might have reduced exploitation by geese of the shared resources. On the basis of our experimental results, we conclude that in this salt- marsh system competition for food with brent geese plays a role in the habitat use of hares, and that hares can reduce goose exploitation of shared habitats.