Defining corridor functions for endemic birds in fragmented south-temperate rainforest

For five species of endemic understory birds (families Rhinocryptidae, Furn ariidae) inhabiting fragmented temperate rainforest in southcentral Chile, we distinguished between vegetated corridors functioning as living space an d those potentially suitable for short-distance movements only. In the firs t phase of the study, we surveyed 24 forested corridors less than or equal to 50 m wide using passive and song-playback censuses. Corridor width deter mined species presence or absence, whereas the number of individuals increa sed with width and understory vegetation density. Birds were infrequently e ncountered in corridors less than or equal to 10 m wide but were always pre sent in corridors 25-50 m wide. Birds present in intermediate-width (11-24 m) corridors were detected significantly less often during passive than pla yback census, suggesting that these birds exhibited conspicuous territorial display less frequently than those present in wider corridors, where passi ve and playback census yielded similar detection rates. Corridors approxima tely 10-25 m wide, therefore, may be transitional between corridors too nar row for most regular uses and those sufficiently wide for birds to establis h territories. Also, bird abundance decreased as the ratio of corridor leng th to width (L/W) increased. Almost no birds were detected in corridors wit h L/W greater than or equal to 10, suggesting the existence of a threshold value for the influence of L/W on corridor use. In the second phase of the study, taped-song playback experiments in corridors less than or equal to 1 0 m wide showed that all five species traveled in them for short distances: 52% of respondents moved up to 50 m from forest patches into narrow corrid ors. Availability of dense understory vegetation was the primary predictor of birds' responses to playback and may determine their willingness to use minimal corridors for short movements. We suggest that corridors for endemi c rainforest-understory birds living in agricultural landscapes of southern Chile can be designed to fulfill distinct functions.