Diet and time-activity budget of White-backed MousebirdsColius coliusin south-western South Africa

Mousebirds (Coliiformes) are unusual in having an exclusively vegetarian diet that includes substantial foliage and by using huddling and sunning to assist thermoregulation. Although previous studies have identified plant species and plant parts consumed by mousebirds, the relative importance of different food types in the diet of wild birds has not been investigated. Furthermore, there is limited information on the extent and importance of their sunning behaviour in the field. We investigated the diet and time-activity budget of White-backed Mousebirds Colius colius at a coastal site in Western Cape province, South Africa. Their diet consisted mostly of leaves (56% of items) and fruits (39%), but diet composition varied with time. Leaves had significantly higher protein content than fruits. White-backed Mousebirds spent most of their time (96%) in stationary activities, particularly sunning (60%), and allocated little time to feeding (4%). However, the proportion of time spent on different activities varied with weather conditions and ambient temperature. When sunning, birds oriented their ventral parts towards the sun 93% of the time, suggesting that exogenous heating may be important for digestion.