The plantcutters (Phytotoma), a group of three endemic Cotingidae from southern South America, are the most folivorous passerines yet known. The white-tipped plantcutter (Phytotoma rutila) is a partial migrant that is widespread in South America, yet little is known about their migratory behavior and diet in Argentina. Our objective was to study P. rutila dietary preferences, feeding behavior, and site fidelity, for a migratory group occupying coastal woodlands in Argentina. The sampling was done during the non-breeding season (winter; April to August) before the spring migration, during 2013-2015. The study site was Pereyra Iraola Biosphere Reserve, Buenos Aires. We performed direct observations of feeding activities with a telescope along a 2.3 km transect. For every individual we recorded sex, species of plant consumed, feeding elevation, and time. After identifying the plant species consumed, we performed a survey to quantify availability of those species at the study site along a 2.3 km transect (every 100m). We calculated a selection coefficient by dividing proportion consumed and proportion available. For analyzing site fidelity, we performed mist netting and banding of individuals during June-July 2013- 2015.
Results/Conclusions
Plantcutters occurred mostly in male-female pairs, and consumed only three plant species (45 feeding occasions): Celtis ehrenbergiana (0.22 of feeding occasions), Lycium cestroides (0.64) and Solanum amygdalifolium (0.13). Mean feeding time was 2.3 minutes and elevation 3.62 m. The availability survey at the study site resulted in a total of 92 individual plants recorded. Selection coefficients were 0.96 for Celtis (0.87 males, 1.04 females), 1.08 for Lycium (0.85 males, 1.29 females), and 0.76 for Solanum (1.88 males, 0.00 females). We banded 24 individuals (14 males and 10 females), and 6 individuals (4 males, 2 females) were relocated at the site. Our results highlight the site fidelity and high selectivity in feeding behavior for plantcutters, feeding from only three plant species at the study site. In contrast with other plantcutters, White-tipped Plantcutters consume only dicotyledons. Plantcutters did not show strong preference or avoidance within selected species, but females preferred Lycium while males were the only ones to consume Solanum. Plants within the Lycium genus were also preferred by White-tipped plantcutters in Cordoba and Mendoza, Argentina; these plants are perennial, rich in proteins, and low in phenols, which make them attractive for individuals trying to maximize energy intake before migration.