Walia Special Edition on the Bale Mountains (2011) - Zoologische ...

Survey method – Dec 06-Jan 07
Line transects (Buckland et al. 2001; Ross and Reeve 2003) were established in sample arrays that
were randomly predetermined on grid cells in a map of each field station. A minimum distance of
1.5 km was used between two neighboring sample arrays; this distance was assumed to be sufficient
to avoid double detection.
A systematic set of parallel lines were randomly superimposed onto the survey area in the
bamboo and bamboo-mixed forest stations. Each sample array had eight straight parallel lines of
0.7 km length for each. The parallel lines were spaced at 100 m intervals following the slope. An
average speed of the surveyors was set to 1 - 1.5 km/h. In total, 128 lines covering a total of 89.6
km in length were sampled in total.
In the non-bamboo forest, a single transect was surveyed along the road and established
footpaths. An average speed of the surveyors was set to 3-5 km/h; the speed differed from that in
the bamboo because of local conditions. In sum, 18 km of transects were surveyed in this strata.
The effective width of each sides of transects were surveyed. We recognize that the use of the road
for establishing the sampling transect potentially introduces a bias, however, because this habitat
was not a priority, we included it only to verify that the Bale monkey is not common in the habitat.
The data that were recorded included: (1) time at which survey started; (2) time at which
animals were located; (3) group size; (4) the location of animals, (5) physical substrate (e.g., ground,
plant species) on which sighting made, (6) observer-animal (nearest) distance and angle relative to
transect line (including height above the ground at which the animal was located), (7) activity of
animals, (8) animal’s behavior in response to observer, (9) environmental factors (cloud, rain, main
rivers, dominant trees, anthropogenic information) and (10) time at which search ended. Binoculars,
video and cameras were used to assist the assessment.
Second field survey - August 2007
The survey in the bamboo forest and mixed bamboo forest was repeated in the previously sampled
areas in August 2007. A few additional sample sites were established to increase sample size. No
sampling was conducted in the non-bamboo forest because no sign of the Bale monkey had been
recorded during the previous survey.
Some other modifications were made to survey method to increase the efficiency of sampling.
Unlike the first period, the area sampled and distance between sampling lines were not fixed. Rather
area and distance between lines was based on the nature of the habitat, specifically, accessibility and
slope. A transect length for each sample site was set between 4-5 km. During this survey a total of
eighteen sample sites were established, for a total length of 79 km, with an average sighting distance
of 46 m within bamboo forest and 61 km within bamboo-mixed forest. Otherwise, data recording
format and surveying techniques followed the previous approach.
<strong>Walia</strong>-<strong>Special</strong> <strong>Edition</strong> on the Bale Mountains 83