HOME RANGE AND HABITAT SELECTION OF CRESTED SERPENT-EAGLE (Spilornis cheela Hoya)
Date Issued
2011
Date
2011
Author(s)
Chou, Ta-ching
Abstract
The Formosan Crested Serpent-eagle (Spilornis cheela hoya) is regarded as the largest subspecies of the Serpent-eagle and endemic to Taiwan. The survival of endemic species limited to one region or on little island are especially more likely to be threatened. Quantitative researches about their demand for the use of space and habitats in this region are very limited. Gather information on the habitat requirements and utilization of a raptor species will improve the development and effectiveness of management plan for its conservation.
I studied the home range and core areas of a native population of Crested Serpent-eagles in southern Taiwan by radio-telemetry from November 2005 to May 2007. Geographic information system were used to assess size of ranging area and as well as habitat composition. Mean home range areas for eight male and six female individuals were 16.65 km2 and 6.93 km2 based on the estimation by the minimum convex polygon (MCP) method and 4.50 km2 and 1.46 km2 by the 95% fixed kernel (FK) method, respectively. Mean core areas for male and female were 1.16 km2 and 0.36 km2 based on the estimation by the AIM (Area Independent Method) and 0.64 km2 and 0.20 km2 by the 50% FK method, respectively. Mean kernel home ranges of male eagles were 3.2 times greater than those of females, and AIM core areas of males were 2.9 times greater than those of females.
All of the individuals exhibited core area overlap, especially in the case of male to male core areas. Female to female core area overlap was on average 1.9%. The same female had on average 14.9% of its core area overlapping with that of another male’s core area. Male to male average core area overlapping was 37.0%. These three combinations of core area overlap ratios were statistically significant. In general, relationships of female-female at the level of core area showed range exclusivity than female-male and male-male. Male core areas were considerably shared with the other same sex and opposite sex birds, but the core areas of female eagles were smaller and showed an extremely low level of sharing with other females. Since female eagles were 18% heavier than males, the difference in spacing pattern may be related to female dominance.
In dry season, significant differences were observed between sexes in 95% FK area, but not in MCP home range. Annual and dry season home ranges were similar between ages, but in wet season subadults had smaller MCP home range then adults and juveniles. There was no seasonal difference in the MCP home range and 95% kernel area using by the total individuals or subgroups of males, females, adults and juveniles.
Compositional analysis (CA) approach and distance-based analysis (DA) approach were adopt to test whether eagles selected particular habitats at two scales: selection of home ranges within the study site and selection of habitats within home ranges. Both DA and CA methods demonstrated that habitats used nonrandom in both study area scale and home range scale, however, only two top-ranking habitats, mixed forest and Acacia confusa forest, typically secondary forest, were the same for different habitat analysis techniques.
According to this research, Crested Serpent-eagles were sedentary to their ranging area in southern Taiwan. No distinct seasonal ranges shifting or migratory behavior was observed among banded individuals. Local population displaying with high density and exerting all types of forest habitat provide a supplement to the phenomenon of insular syndrome.
The results of this study contribute to identifying Crested Serpent-eagles’ vital attributes of home range size, habitat components, and relative proportional habitat utilization, which may probably be applied to planning habitat conservation and forest management plans for them and related species.
Subjects
radio-telemetry
home range
core area
space use
habitat selection
Spilornis cheela hoya
SDGs
Type
thesis
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