Tuesday, November 1, 2011

Counting Ibex in Mongolia

First week of October I started on an enormous task of estimating the population of Ibex in the Tost and Tosunbumba mountains in the South Gobi region of the Mongolia. After scouting around, getting used to the area for the first few weeks I started the actual work only in the last week of October.

The Steppe of Gobi and the Tost mountains in the background

The Tost-Tosunbumba mountains cover an area of about 2000 km2 and are almost in the middle of the Gobi desert. There is very low precipitation and temperature fluctuates between 30 degrees in the summer to -30 in the winters. Temperature now (Oct- Nov) hovers between -10 at night and 4 during the day. The mountains are not very high, the base of the mountain is at about 1800m and the highest summit rises only a little above 2500m. The terrain is very rugged in parts and absolutely gentle and rolling at others.

A rutting male ibex with a female.

I have divided the entire landscape into smaller units ranging from 20-150 km2. The larger units are further divided into smaller grids of ~20-30 km2. I am using a method developed by Forsyth and Hickling (1997) to count the Himalayan Tahr in the South Isle of New Zealand. In this method, one does a double count of all the herds in the survey area. Based on the age-sex classification of individuals in a herd, the observers the find out the herds that were counted only during the first survey, only in the second survey and herds counted in both the surveys. Using the differences in counting in both the surveys the observers then estimate the probability of detections which then helps to estimate the number of groups that were missed in both the surveys. The method relies on the robust mark-recapture theory.

It is the solitary animals or the small groups that are harder to detect!

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