Lemur Population report

Species Diversity

Between the 22nd July and the 12th September 1999 four species of lemur were recorded in the Ifotaka Forest as illustrated in Table One below

Table 1  - The lemur species present in the Ifotaka Forest July-Sept 1999
 

Initially the aim was to make population estimates for all four species, however constraints of time and feasible methods meant that this was only possible for Propithecus v. verreauxi. Lepilemur leucopus was only sighted on two occasions and Microcebus murinus was sighted on around ten occasions.

Lemur catta was observed to be at high densities and so the locations of groups encountered has been recorded on a sketch map however due to their terrestrial nature and grey coloration sighting at any great distance from the riverbed proved impossible and so population density estimates could not be produced. 

Wild population densities of Malagasy lemurs outside protected or managed areas have not previously been estimated (Simons, 1997), for this reason the principal aim of Project Ifotaka 1999 was to provide estimates for the diurnal species inhabiting the forest. Two methods were employed to obtain estimates of population density.

1. Transect Walks: The transect, illustrated on Map 2 with a red arrow was placed along the Asantoria riverbed from the hamlet of Morafeno to the village of Andavatsak. The transect was 12Km in length and was dry during the survey period in July and August 1999. The transect was split into 500m sections and the field of view for each of these was estimated visually aided by FTM Map K-61. The 500m sections were then grouped into 4 sections and each was surveyed by a pair of students from Durham four times, twice shortly after dawn (0630-0930)(once in each direction) and twice shortly before dusk (1530-1730) (again once in each direction). The pair, accompanied by a local guide walked at \'981.5Km/hr scanning the area with the naked eye and 10X50 Binoculars. One person was responsible for each side of the river valley. Upon sighting a group of lemurs the team would stop for 10 minutes to determine the size of the lemur group, data recorded included species, group size, location (on sketch map) and time of sighting. The survey would then continue. The mean of the four survey results was calculated to produce the density estimates illustrated in Figure One. This method provided sufficient data to estimate population densities of Propithecus v. verreauxi and recorded the presence/absence of Lemur catta\

2. Point Counts Upon completion of the transect walk surveys it was deemed necessary to compare that method with an alternative to determine if the vegetation adjacent to the riverbed supported different population densities to the hilltop vegetation.

Six survey points were chosen on prominent locations with large areas of visibility, again in the area of the transect (riverbed) - see Map Two. Typically cliff tops and hilltops were used by the survey teams which consisted of two Durham students assisted by one local guide. The teams remained at each survey point from 0700 to 1700 for 2 consecutive days. The survey area was determined using FTM map K-61 and visual distance estimation. For each 15 minute period of the survey the number of groups visible and the size of each of these groups was recorded along with their location on a sketch map.

Table 2 : Population density of Propithecus v. verreauxi from Point Count surveys \par (individuals per sq Km, August 1999)
 

Table 2: Summary Data on Population Density and Group Size from both surveys.(July - August 1999)