Toxic Scat: A Mechanism to Prevent Overdosing on Plant Chemicals by Grouse

Although abundant and accessible, plants pose significant challenges to herbivores. The high fiber content and relatively low nutritional value of plants compared to animals makes plants a particularly difficult food source for birds. For example, birds lack teeth required to reduce particle size and flight limits the size and complexity of the gastrointestinal tract (Dudley and Vermeij 1992) required for fiber digestion. These limitations are thought to explain why herbivory is a rare foraging strategy in birds. A less studied explanation for limited herbivory in birds may also be the diversity of chemical defenses in plants. These chemical defenses can be toxic to herbivores and energetically costly to detoxify (e.g. Glick and Joslyn 1970, Lindroth and Batzli 1984, Robbins et al. 1987, Guglielmo et al. 1996, Sorensen et al. 2005). Similar to the limited digestive capacity, flight may limit the size of the liver which is the major organ used to detoxify and eliminate ingested toxins.