Folivory in the white-tipped plantcutter Phytotoma rutila: Seasonal variations in diet composition and quality

Abstract

Plantcutters (Phytotomidae) represent the only Passeriformes with a predominantly folivorous diet. Little is known however about their feeding habits and adaptations for leaf consumption. Here we analyze the relationship between diet composition and nutritional value in the white-tipped plantcutter Phytotoma rutila in a Chaco woodland in Córdoba, Argentina. The white-tipped plantcutter consumed mainly dicot leaves (91%), complemented with a small proportion of fruits (7%) and flowers (2%). Eleven plant species were utilized, of which five were strongly dominant: Lycium cestroides (38%), Prosopis alba and P. nigra (28%), Celtis tala (22%), and Schinus longifolius (8%). No animal food was consumed. The leaf material ingested by the white-tipped plantcutter had high protein content and low proportion of fibers and phenols. In multivariate analysis, leaf chemical properties accounted for over 81% of the variation in diet composition throughout the year. However, only protein and phenols content related significantly with diet composition in single regressions. The quality index that relates protein with lignin and phenols showed the highest correlation with diet composition. Availability of highly nutritive leaves of Lycium cestroides during the dry season seems to be a key factor for the occurrence of the white-tipped plantcutter in the study area. Our results confirm that plantcutters are truly folivorous passerine species, being able to obtain a highly nutritional diet throughout the year.