- Tiger numbers potentially increased 40% in seven years – from 3,200 in 2015 to 4,500 in 2022 – representing the first climb in decades (according to a 2022 announcement by the IUCN).
- Exciting news but cautious optimism is recommended as advances in methods used when counting tigers may explain a possible increase.
The systematic counting and monitoring of tiger populations began in the 20th century as wildlife conservation efforts gained momentum. Since then, advances in technology and statistical techniques continue to improve the accuracy and efficiency of tiger population monitoring methods. This begs the question, is the announcement in 2022 by the IUCN of a 40% increase in tiger numbers backed up by robust data?
Historical methods for counting tigers
Historically, people have employed various methods when counting tigers. Here are some of the common approaches used in the past:
- Direct observations: Early methods relied on direct visual sightings of tigers by counting the number of tigers seen in a particular area. This method can be difficult and time-consuming, and it is often not possible to get a complete count as tigers are elusive and secretive animals.
- Indirect observations: This involves using other methods to estimate the number of tigers, such as counting tiger tracks, scat (faeces), or kills. This method had limitations due to the difficulty of differentiating individual tigers. A researcher may be able to say with confidence a tiger exists in a particular landscape but not necessarily how many.
Due to the limitations of these early methods, historical estimates of tiger numbers are hard to verify and very difficult to set up as baselines to measure growths and declines in populations. Over time, conservation organisations and researchers have been refining these methods and using a combination of approaches to improve the accuracy of tiger population estimates.
Modern-day methods for counting tigers
Counting global tiger population numbers is still a complex and challenging task that requires a combination of field surveys, advanced statistical analysis, and the use of technology. Here are some of the methods that are now more commonly employed to count tiger numbers:
- Camera Traps: These devices are equipped with motion sensors and are strategically placed in tiger habitats. When an animal passes by, the camera is triggered and captures images or videos and researchers can identify individual tigers from these based on their unique stripe patterns.
- Spatially Explicit Capture-Recapture: This is a statistical modeling approach that combines camera trap data with spatial information. It considers the spatial distribution of individual tigers within the study area to estimate population density more accurately.
- Line Transect Sampling: Line transect sampling involves walking along predetermined paths, known as transects, and recording direct tiger sightings or indirect signs. The data collected is used to estimate population density and distribution using statistical models.
- Genetic Analysis: Researchers collect DNA samples from tiger feces, hair, or other biological materials found during line transects. By analysing the genetic profiles of these samples, researchers can identify individual tigers and estimate population size, and genetic diversity.
- Satellite Imagery and Remote Sensing: Researchers analyse satellite images to identify suitable tiger habitats, monitor land cover changes, and assess landscape connectivity, which can indirectly help estimate tiger population sizes.
- Citizen Science and Community Involvement: In some cases, citizen science initiatives and community involvement play a role in tiger population monitoring by reporting tiger sightings and signs, collecting data, and participating in conservation efforts.
These days most countries are using similar methods to count tiger numbers, but everyone is facing the same difficulties. Tigers are elusive and well camouflaged and have large home ranges which can be hard to cover in a survey. They are primarily nocturnal animals living in habitats that are not always accessible and camera traps don’t always capture a tiger’s stripe patterns well enough.
Have Global tiger numbers gone up in the last decade?
The 3,000 tigers that were estimated to remain in the wild in 2010 formed a baseline for the global recovery of tigers. This figure was used to guide the Tx2 goal of doubling tiger numbers by 2022. However, not all tiger range countries had been able to use statistically robust methods pre-2010 to create reliable baselines. India and Nepal represented the very few countries that had been using camera trapping to estimate numbers, whereas many countries in Southeast Asia were still using pug marks and other indirect signs to make baselines (take a deep dive into India’s big tiger count). But, even for the countries employing more advanced methods, multiple techniques have been tested over the years and sampling has expanded and intensified. It is likely more tigers are included in the counts because of this which adds to the difficulty in comparisons over time. But this is how science works; you move from one method to another, continuously evolving to measure variables more effectively.
Is it required that we know the exact number of tigers in the world?
Population ecologists are not just interested in tiger numbers. Other vital parameters are needed to get the full picture of the health of these tiger populations, measure conservation outputs, and predict their future survival. These include studying metrics like unnatural mortality rates which could be depressing the population, poaching of prey base, individual survival probability, female tenure of a landscape, fertility, and the survival and dispersal rates of cubs.
A lot of time, effort, and money is spent by countries to measure tiger numbers which, in some places, may be better directed to targeted conservation actions to improve the state or health of tigers. Nonetheless, the measure of tiger numbers has been a useful tool in setting recovery targets, especially landscape-specific targets which are easier to measure. Baselines are also critical when contemplating reintroduction and supplementation programs and helpful at a site level which is easier to measure. What is harder is going from a single estimate to an extrapolation for a landscape. It is very statistically complex to estimate how many tigers there are in a country based on small samples.
Can claims of increases in global tiger numbers lead to complacency in their protection?
Numbers that may not be reflective of true trends in tiger numbers could eventually lead to the up listing of the species on the IUCN Red List. We, of course, want tigers to move away from the endangered categorisation, but only if that’s not happening due to mistakes we’ve made with counts. It must be true growth that we track otherwise the changing status could result in complacency in funding agencies. If tigers are considered recovered, then there is a chance that the already small pot of conservation funding directed at the species could be reduced further affecting their future survival.
This blog was written based on a WildCats Pawcast episode with Population Ecologist and Assistant Director of Panthera’s Tiger program Dr. Abishek Harihar. Since joining Panthera in 2015, Abishek has been primarily involved in standardizing camera trap designs and more broadly population monitoring for Panthera’s Tigers Forever program. He also contributes to developing metrics to evaluate the effectiveness of conservation actions across Panthera’s Tigers Forever sites. You can listen to the full episode via the link below.