How elephants are counted

Sub : Env

Sec: Species in news

Context:

The Environment Ministry has delayed the release of the “Status of Elephant in India 2022-23” report, citing incomplete census data from the Northeast. The report for other regions is ready but will not be released until June 2025.

Decline in Elephant Populations:

Preliminary data shows a sharp decline in elephant populations, particularly in:
- Southern West Bengal (84% decrease)
- Jharkhand (64% decrease)
- Odisha (54% decrease)
- Kerala (51% decrease)

Reasons for Decline:
- The report attributes the decline to factors like unmitigated mining, linear infrastructure projects, and other developmental activities.

Counting Methods:

The elephant census has evolved significantly since the 1990s:
Old Methods:
- Total Direct Count (Pre-2002): A basic headcount of elephants, which lacked scientific accuracy.
- Indirect Dung Count (Post-2002): Surveyors counted elephant dung along pre-designated forest paths and used the dung decay rate and defecation rate to estimate populations.
- Sample Block Counts: Surveyed limited areas (5 sq km) to maximize detection and then extrapolated to estimate populations across larger areas.
New Method (2022-23 Census): The 2022-23 census used a genetic mark-recapture model. Instead of visual identification (used for tigers), elephant dung samples were analyzed for genetic markers to identify individual elephants.

Mark-Recapture Method:

This statistical method uses recaptured individual photographs (for tigers) or dung DNA (for elephants) to estimate population density and extrapolate numbers for areas not directly surveyed.
The Synchronous All India Elephant Estimation 2022-23 (SAIEE 2023) differed from this tiger census method in only one aspect: it used a genetic mark-recapture model.
The elephant hide has no unique markings like tiger stripes. So elephant dung samples collected during ground surveys were analysed in the lab to identify unique elepphants.

Tiger and Elephant Census Harmonization:

In 2021, India announced plans to harmonize tiger and elephant population estimation.
In this method, the entire forest area is broken down into similar-sized cells or blocks (say, A, B, C, and D) where ground surveys are conducted to look for tiger signs (pug marks, droppings, etc.) and identify tiger-occupied forest cells (say, A, B and D).
The survey also assesses a range of “co-variates” — common variable factors such as the quality of vegetation, availability of prey. distance from water/ nightlight, degree of human disturbance etc. – to determine the relative tiger-holding potential of these blocks.

Regional Threats:

Habitat loss and conflict are common threats to elephants across India.
Different regions face unique threats to elephants. For example, in Odisha, issues like mining and low-hanging power lines are key contributors to declining populations.

Source: IE