Ranging and territoriality in red-shanked doucs (Pygathrix nemaeus) at Son Tra Nature Reserve, Vietnam.

Abstract

The home ranges of odd-nosed colobines as reported by a number of studies can vary greatly both within and between taxa. Evaluating Pygathrix, particularly within the context of the odd-nosed colobines, has proven challenging due to the comparable dearth of published data on all three species-Pygathrix nigripes, Pygathrix cinerea, and Pygathrix nemaeus. This dearth has also proven challenging when assessing territoriality within Pygathrix and contextualizing this behavior to odd-nosed colobines. For this study, we set out to assess home range, daily path length, and territoriality in a population of P. nemaeus at Son Tra Nature Reserve in Vietnam. We collected a total of 259 h of behavioral data using 10-min focal follows with 1-min instantaneous scans, including GPS recordings for each follow. We collected phenology and weather data, which were then used with Pearson's correlations to test whether ecological factors influenced variation in ranging or daily path length at both the monthly and seasonal levels. Finally, we used the Mitani-Rodman defendability index to assess territoriality in P. nemaeus. We found that our population of P. nemaeus had a home range of 36.00 ha with a core area of 8.02 ha and an average daily path length of 509.11 ± 244.87 m. Daily path length was correlated to precipitation such that daily path lengths were shorter during increases in rainfall (r(17) = 0.52, p = .03). These measures resulted in a defendability index of 0.75, suggesting that the population of P. nemaus on Son Tra does not travel far enough each day to actively defend territorial borders.