The Influence of Willow Salix sp. Rose Insect Galls on Moose Alces alces Winter Browsing

Abstract

Feeding trials were conducted with Moose (Alces alces) habituated to people to determine whether Moose prefer winter shoots of Scouler’s Willow (Salix scouleriana) with or without leafy willow rose insect galls created by rosette willow gall midges (Rabdophaga spp.). After sampling one or two shoots with galls, each Moose in the feeding trial showed a clear aversion to the galls and dropped or spit out parts of the willow shoot containing these structures in subsequent feeding bouts. Despite the reported importance of leafy materials in the fall and winter diets of Moose, these results suggest that morphological attributes of or chemical deterrents within galls may lead Moose to reject these structures in favour of gall-free shoots. Why galls are rejected is speculated upon, but remains untested.