Lophozonia tree cavities used for nesting by Slender-billed Parakeets (Enicognathus leptorhynchus) in the central valley of southern Chile: a potentially vanishing keystone resource

摘要

Background: The Slender-billed Parakeet (Enicognathus leptorhynchus) is a psittacine endemic to southern Chile and an obligate secondary cavity-nester. In the central valley of southern Chile, most (94%) of the known Slender-billed Parakeet nests have occurred in large, mature southern beech (Lophozonia obliqua) trees (locally known as "pellines"). As relicts of the original old-growth forests of southern Chile, most pellines have been lost due to extensive land-clearing throughout the region, potentially threatening long-term persistence of the Slender-billed Parakeet. Methods: We conducted our study in the central valley of southern Chile, near the city of Osorno during three con-secutive nesting seasons (November–January, 2008–2011). Nest trees used by Slender-billed Parakeets were located by direct observation of parakeet activities and through interviews with local residents, some of whom were former parrot nest poachers. Nest cavities were accessed, inspected and measured using single-rope climbing techniques. We report means, standard errors, 95% conifdence intervals and ranges for 11 cavity-related variables. We also report clutch sizes encountered in active nests, and age estimates of nest trees based on known growth rates ofLophozonia trees in southern Chile. Linear regressions were used to evaluate potential relationships between cavity-related vari-ables and clutch size. Results: We located and measured 38Lophozonia tree cavities used for nesting by Slender-billed Parakeets. Com-pared to those used by other psittacines, nest trees were relatively large, averaging 30.4± 1.1 m in height with a mean diameter at breast height of 134.5± 4.7 cm. Based on estimated annual diameter increment, ages of nest trees ranged from approximately 209–485 years. Nest cavities entrances averaged 12.5± 0.9 m in height above ground level. Cavity entrance widths averaged 51.0± 13.3 cm (vertical) by 11.5± 0.7 cm (horizontal). Cavity entrance orienta-tions were apparently random, with no directional preferences detected. Nest cavities were also relatively large, with a mean internal diameter of 39.6± 2.4 cm and mean depth of 90.3± 24.2 cm. Clutch sizes (2–9) were unusually large for psittacines of this size (ca. 280–300 g) and broods of up to seven well-developed nestlings were observed. Conclusions: We found that the deep and spacious cavities provided by pellines facilitate successful rearing of large broods, thereby maximizing productivity and iftness. The existence of pellines has apparently allowed Slender-billed Parakeets to adapt successfully to a wholesale loss of ancestral habitat to anthropogenic modiifcations. Immediate and strategic conservation measures, such as protection of existing pellines and the regeneration and recruitment of additional ones, are recommended for ensuring the survival of Slender-billed Parakeet populations throughout the central valley of southern Chile.