Abstract

In South American temperate rainforests, five endemic understory birds (four Rhinocryptidae and one Furnariidae) are often associated with the main understory plant, the native bamboo Chusquea valdiviensis (Poaceae: Bambusoideae). We studied the effects of bamboo cover on species abundance and richness of those understory birds and explored the functions of bamboo as food resource and escape cover. In Chiloe Island (42degreesS), southern Chile, we selected four old-growth forest patches >100 ha and in each patch conducted bird surveys in six plots with >70% understory cover. Three plots were dominated by native bamboo and three plots had a sparse bamboo cover. Bird abundance (point counts) was significantly correlated with both total understory cover and percentage of bamboo cover but was not correlated with other kinds of understory plant cover. Bird species richness was positively correlated with bamboo cover and negatively correlated with other kinds of understory cover but unrelated to total understory cover. Leaf-gleaners Magellanic Tapaculos (Scytalopus magellanicus), Ochre-flanked Tapaculos (Eugralla paradoxa), and Des Murs's Wiretails (Sylviorthorhynchus desmursii), and the ground-gleaner Chucao Tapaculos (Scelorchilus rubecula) were more abundant in high-bamboo plots; but the ground-gleaner Black-throated Huet-huet (Pteroptochos tarnii) was recorded more times in plots with low-bamboo cover. Availability of invertebrates per unit of understory dry mass did not differ between high- and low-bamboo plots; but plant biomass was greater in high-bamboo plots, so total invertebrate abundance per plot was higher there. Ground-litter invertebrate abundance was similar in all plots. To examine escape-cover preferences, nine captured Chucao Tapaculos were released in front of two different understory scenarios (high-bamboo cover or bamboo-free understory); 88% of released birds moved into bamboo cover. We suggest that the structure of native bamboo understory is critical for the maintenance of four of those species, and retaining bamboo cover in managed stands may help minimize the effect of logging on understory birds.