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Foss, John – Occurrence and habitat associations of diurnal raptors along the Bio-Bio River, Chile. 1994.

The biodiversity of the Bio-bio River ecosystem is under imminent threat from a plan to build a series of six hydroelectric dams over the next decade. The purpose of this project was to survey pre-dam diurnal raptor species presence and habitat use along the Bio-Bio River corridor. My objectives were to: 1) establish areas of local species occurrence; 2) compare species abundance, richness and diversity in selected habitats; 3) examine patterns of habitat association; and 4) provide baseline data for future ecological monitoring.

The survey comprised an opportunistic, downriver, boat-based survey, and a terrestrial, limited distance point-circle count at selected study sites in the 165-km transect along the Bio-Bio River. Observations during the ten survey trips (1992-1993) produced an overall count of 12 diurnal raptor species and 419 individuals, with 255 individuals observed during the downriver survey, and 164 individuals observed during the terrestrial point-count survey. The highest species abundance occurred during the downriver survey (255), while the highest species richness index was recorded during the terrestrial point-circle count (12) survey. Species diversity varied between the two methods with mean values of (H‘=1.90, H‘=2.05) for the downriver and terrestrial circle-point count, respectively. Along an environmental gradient, the most productive habitats for species abundance are located between river km 100-140. The most productive habitat for species richness, abundance, and diversity in the downriver survey was located in disturbed areas, whereas Nothofagus woodland supported the highest indices in the terrestrial circle-point count survey. Andean condor, peregrine falcon, and bicolored hawk may function as individual indicator species or as a guild of habitat specialists that could be used to monitor environmental change along the Bio-Bio River corridor.

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