A review of tiger conservation studies using nonlinear trajectory: A telemetry data approach

2.1 Database string search

To capture the maximum number of studies conducted on tigers using telemetry data over database Scopus (www.scopus.com), the strings used are string “wildlife” and “Conservation studies” and “tigers.” Another string used to catch all the literature of telemetry studies is “Telemetry studies or radio telemetry” and “tigers.” To retrieve all the papers relating to telemetry studies on tigers is a challenge as most papers describe the region of study instead of the data used for the conducted study. One more string used to capture all papers is “telemetry studies” and “tigers” and “India.” These strings on Scopus database after removing the duplicate entries have yielded 301 documents. To conduct the review on the yielded documents, the following methodology was used (Figure 1).

Figure 1

The flowchart shows the process of filtering papers from database search for the review conducted in this study. Here n represents the number of papers for the respective block [52].

The selection criteria for the studies to be included in this review was based on the below mentioned criteria. Total no of studies yielded from database search on the abovementioned strings was n = 301.

1. The study related to wildlife conservation of terrestrial mammals was found out to be 289 and 8 studies were not related to wildlife conservation and hence were not included.

2. It is found out that from these 289 studies, only 242 were related to studies on terrestrial mammals and the rest 47 were conducted on conservation of ocean species, birds, reptiles, and vegetation/fauna of the region. Hence, only 242 studies were included for the further selection criteria.

3. From these 242 studies, only 104 were related to tigers and the rest were related to other terrestrial mammals such as leopards, elephants, wolf etc.

4. Studies related to tigers are found to be 104 from these studies, and only studies from India or related to India were taken into consideration. The number of studies on tigers from India was found to be 50, and from other countries, a total of 54 studies were conducted from our search string over the Scopus database.

5. From these 50 articles, 7 studies were conducted on tigers using radio collar or telemetry data. Rest 43 studies were conducted using camera trap, sign survey, scat analysis, and other methods to understand the tiger’s ecology. These seven studies are tabulated in Table 4.

Although these seven articles are peer reviewed research on telemetry studies in India over the past two decades, we also want to declare that this document search string may not have included or captured all the work for this topic. We have presented a systematic review, along with these seven articles, and many more were reviewed as cited in the references.

In this work, detailed bibliometric analysis has also been done using VOSviewer [53] to analyze the efforts for conservation studies. The analysis is done on the documents retrieved from document string search over Scopus database. From this analysis, the below table is formed. (Table 1).

These data show the top countries publishing research on wildlife conservation according to the methodology used in this study. India has substantially more no of studies as compared to other countries followed by United States and United Kingdom among the top countries. It shows the efforts of the countries toward improving the conservation strategies. The data not only show that the average citation is maximum for Brazil but also the total link strength which is the collaboration among the countries is zero. United States shows the maximum collaboration with other countries. But the trend here shows that apart from the countries where remaining tigers of the world are found such as India, Nepal, Bhutan, China, Thailand, Bangladesh, Malaysia, Indonesia, Russia, and Myanmar and few more, other countries in collaboration are also conducting telemetry studies for tigers and contributing in the research publications. Figure 2 shows the link strength of countries among each other. India and United States are top countries in terms of number of research documents published followed by United Kingdom as per the methodology used in this work.

Figure 2

This figure shows the inter-networking of countries producing research studies in the field of wildlife conservation.

Along with top countries contributing to the research on wildlife conservation, top organizations working for conservation of wildlife have also been analyzed. Table 2 shows the top organizations list along with the number of documents published with their average citations. Wildlife Institute of India (WII) has contributed maximum number of documents according to our methodology. Total link strength is 3, which means that it has collaborated with other institutions as well. These numbers are promising for India as it shows the continuous efforts of India toward wildlife conservation in the country.

3.1 How radio telemetry works?

Radio telemetry requires a transmitter and a receiver.

Transmitter: Signals are transmitted using the transmitter and a power source and antenna to propagate the signals using radio waves.

Receiver: Picks up the signals sent by the transmitter with an attached power source.

The transmitter is attached to the animal using a radio collar which transmits the signals to the base station or survey site where the receiver is located. Radio collar is fitted around the neck of animals such as tigers, wild dogs, bears, etc., and to the ankle of animals like rhinoceros, elephants, etc. A radio collar is a device that contains a transmitter and power source to send the signals using radio waves to the receiver. These are designed to have less impact on animals and high on its detectability. To avoid the impact of radio collars on animals, the standard weight of the collar should not be more than 5% of their body weight [9,10,55]. With the advancement in hardware and sensors, few collars weigh around 1% of the animal body weight [4,9,54]. Radio collars are equipped with different types of sensors that can record the movement activity, body temperature, and mortality of the animal [11,12].

Three different types of radio telemetry uses radio-collars to transmit the data.

1. Very high frequency (VHF) radio collars: it is the standard method of collecting telemetry data of the animals by using VHF-based radio collars. An animal wearing a VHF transmitter transmits the signals which can be received by using antenna and techniques like triangulation and homing.

2. Global positioning system (GPS) radio collar: it tracks the animal from a remote location. GPS collars store the data and transmit them at preset intervals. They store the locational data which can be downloaded in many ways [9]. GPS radio collars use the mobile network to transmit the data. These types of collars also come with attached VHF capabilities [9,10].

3. Satellite radio collar: tracks the animal from a remote location. It uses a satellite to transmit the data to the receiver.

Table 3 shows the comparison of different radio telemetry collars used in wildlife. Figures 4 and 5 show the GPS radio collar used for tracking tigers and the tiger fitted with radio collar [4], respectively.

Figure 4

GPS radio collar for tigers [4].

Figure 5

Tiger wearing a radio collar [4].

3.2 Recent trends and applications of telemetry

1. Radio collars with inbuilt cameras: these collars can help to record audio and video of the surroundings of the species [11,12].

2. Radio collars with temperature sensors: this recent development in radio collars allows the collection of temperature data of the surroundings as well as of the animal body [11].

The literature survey presented in this study has not found the use or mentioning of any of these new radio collars but they have promising features which can change the facet of telemetry studies. Telemetry can be used to study the movement patterns, habitat usage, social interaction, home range, food habits, mortality rate, land use, migration patterns, behavioral patterns, and human–animal interaction. There are many conservation areas where it is impossible or very difficult for humans to carry on surveillance activities. This is where telemetry studies play a huge role and provide an understanding of various tiger behaviors as mentioned above. But majorly telemetry is used for studying the movement pattern and habitat use of species.

Movement Pattern: the meaning of movement pattern in the wild means how the space is used and how animals move in context to anthropogenic activities. Studying the movement pattern decodes other traits of the species such as:

Movement patterns help to understand their territory or their home range size which helps to understand the prey density in the area [10]. This is because prey base is directly proportional to the tiger density in the region.

The abundance of prey density determines the presence of tigers in the area [13]. Tigers usually prey on large animals such as bulls, gaurs, rhinoceros, wild boars, etc. [14].

Analyzing movement patterns helps to understand their social behaviors and their spatial–temporal interactions. It also suggests the use of demography by the tigers [15]. Due to fragmented land spaces, movement pattern studies suggest how the movement and activities of tigers are influenced by human presence. To study the movement patterns of species, large number of locations per tiger is required. Dispersal data collection is very difficult to collect as they move very long distances very quickly [10]. But radio telemetry has made it possible to collect data in a contiguous manner with the help of VHF/GPS radio collars [16]. Over the past decades, many tigers are radio-collared to understand their movement and ecology. Dispersal movement and its collected data are very crucial as they can provide the basis to create green corridors for already fragmented forest land [17,18].

Habitat Use: the meaning of habitat is the space where the animal can rest, take shelter, and eat. Tigers typically have wide home ranges, their typical home range size for male tigers is 60–150 km² and for female, the home range size is 20–60 km² [2,17]. Studying habitat use is a challenging task as tigers prefer to stay in the core areas of the forest. These areas are difficult to track, sometimes GPS/satellite collars also do not work properly due to canopy cover [10]. Tigers have a variety of habitat across India from mangrove swamps of Sundarbans to terrain areas of the Himalayas, rain forests of eastern and western Ghats to the tropical moist deciduous forest of central India and dry forest of Rajasthan [18]. Tigers walk at a speed of 5 km/h and can reach any area of their home range within an hour [10]. Telemetry studies on collared tigers at Sundarbans have shown that prey abundance is inverse to the home range of tigers. It has also shown that the breeding tigers have an average home range size of 40 km² [10].

3.3 Before telemetry

Telemetry research started in 1963 in India. But researchers are studying tigers for over 100 years [18,19]. Before telemetry, scientists and conservationists were using camera trapping, on-site tracking of the tigers for a long period of time to understand the ecology of tigers [1,18]. Their studies have provided the base of tiger ecology. Traditionally, tigers were tracked by the professional shikaris from their pugmarks to hunt the animal. Other sign analysis included scat analysis. Data collected using these methods have their challenges. Tracking the animal on the field is always dangerous, it causes hindrance to animal activities as well. Using these methods, very limited data can be collected as unreachable areas cannot be covered by these methods. But studies based on these methods have shown that for a few ecological questions these methods provide better answers such as to estimate population size and distribution of tigers. These methods along with the latest techniques provide high-quality data for analysis which can be used to infer the behavioral patterns of species [20].

Table 4 shows the different data collection methods in wildlife used by the scientist before and after telemetry in India:

3.4 After telemetry

Radio collars were first used in the USA on grizzly bears in early 1960s by Craighead Brothers. They tracked these grizzly bears from 1960 to 1968 and later published their research on the collected data explaining home ranges, movement patterns, food habits, and mortality rates [6,17]. Through telemetry data analysis, researchers were able to manage the habitat area. Studying the home ranges gave the ideas of important locations which could be used as habitat, hence more focus could be given to those areas. Breakthrough in wildlife research after telemetry are as follows.

4.1 How telemetry enhanced the knowledge to understand tiger ecology

Radio telemetry now is extensively used by conservationists. The recent study published in June 2021 was conducted by WII, Dehradun and Maharashtra Forest Department (MFD) in which 15 tigers were radio-collared from 2015 to 2020 to study their movement patterns through telemetry data. This study has shown the pathways and corridors of tiger movement [3]. Through this study, the scientist and researchers were able to identify the pathways of tiger dispersal at Vidarbha landscape, which is home to around 331 tigers [3,9]. The study can guide ways to mitigate human–animal conflict, habitat fragmentation, and how to involve other stakeholders of the land to make better use of land for tiger dispersal without any human–animal conflict. Before the widespread use of telemetry in wildlife, very little was known about their movement and habitat [34]. Studies of telemetry data and with on-field efforts of a conservationist, the habitats of tigers are also known using radio collars/GIS/GPS. These were the landmarks in tiger telemetry in India. These tasks (movement and habitat) were accomplished by the use of technology. Using telemetry data analytics, it was found, how tigers do transboundary movements, satellite technology through radio collar was used to observe tiger translocation from Sariska Tiger Reserve to Panna Tiger Reserve [4].

These technologies have also helped other methods of wildlife conservation, for example, the camera trapping technique of observing animals was in use for so long but was not that effective. Using radio collars on animals gave their movement patterns and ecologists were able to identify the correct locations to put the camera trap. It has also helped in estimating the correct population size of tigers.

Another telemetry study has shown that the radio-collared tigers in Nagarahole Tiger Reserve were more nocturnal. They were least active during the daytime due to human interference in the area. This is an important finding, it suggests the behavior changes in tigers due to anthropogenic activities [13]. It has been observed through radio-collared tigers that tigers move from 2 to 11 km on daily basis. It has also been found through telemetry data analysis that tigers’ habitat selection depends on the density of prey. They disperse to the areas where their prey or ungulates concentrate [13]. Tigers are territorial and generally solitary animals. Through telemetry studies it is shown that they require a large contiguous area of habitat that supports their prey requirements. It is also shown that the tiger movement is usually for hunting or social interaction with other co-predators [1]. Table 5 shows the different studies conducted using radio-collar on tiger in India in the past decade.

These studies are conducted using telemetry data which are collected using radio collars on tigers. The table above shows the number of tigers radio collared to collect the telemetered data. These data have been analyzed to understand the species ecology in more detailed way. In India,there are 52 tigers reserves which are further divided into core area and peripheral area [45]. Figure 6 shows the region on the map of India, over which these major studies were conducted.

Figure 6

Map of India showing the regions of major conservation studies along with the type of vegetations found in these regions.

Telemetry data analyses have provided the insights into ecology of tigers. The studies conducted above in Table 5 have provided the better understanding and awareness about the behavioral patterns of tigers. One of the studies in the table above suggested that breeding tigers have large home ranges with an average of 40 km² at Sundarbans of India. This study has also provided the insights into movement hours of the tigers. It concluded that the tigers move more in the early hours of morning, may be to avoid conflict with humans. If the activities by humans are restricted during morning hours human–animal conflict can be reduced in the area [35]. Another study mentioned in the table above showed that radio telemetry has enhanced the understanding of reintroduced tigers in the area where local population is extinct. The study stated that radio telemetry made it possible to closely monitor the reintroduced tigers, which was not possible earlier [49]. Through monitoring of these nine reintroduced tigers in the region, it appeared that these tigers behaved in the same manner as that of the native population of the region [49]. One more study conducted using telemetry data in the central India has presented that the Pench forest of Madhya Pradesh is relatively small and when tigers disperse, the conditions in the buffer zone of Pench forest is not optimal and can impact the dispersed tigers [48]. One of the studies conducted from the table above has provided insights into how increase in the human population is putting pressure on the already fragmented landscapes. If the species like tigers has to co-exist with humans due to increased pressure on land, then it is highly important to understand the movement patterns of tigers and how they adapt to the challenges outside the protected areas. Their response to the human interventions can help the conservationist to plan the strategies for land use and corridors. All these studies have presented the home range, movement patterns, dispersal, response of reintroduced population, habitat suitability, and many other important factors using telemetry studies on the tigers of India.

4.2 Challenges and issues with telemetry data

There are a few limitations attached with telemetry data collection and analysis. Many ecological questions are answered through telemetry studies, which could not be answered using any other method of wildlife conservation. But there are a few issues while using telemetry studies.

1. The first step to collect telemetry data is to put a radio collar on the tigers, which is a dangerous task as it involves capturing the tiger. To capture the tiger, there are many permissions and approvals required which can be a tedious task [4,8]. Once approved, ecologist and researchers along with the team needs to plan the capture very carefully because while capturing, the animal can be in danger which sometimes can lead to the death of the animal. This can lead to the cancellation of permission for animal capturing that can compromise the research study.

2. During the initial days after attaching radio-collar on species, they have reduced activities as they adjust to the collar. Studies conducted for a shorter period may lack or have insufficient data as during the first few days or weeks, the animal adjusts to the radio collar and hence is less active [38,39].

3. To collect telemetry data needs a high level of expertise, sometimes it is required to be on-site if a standard VHF radio collar is used. Cost associated with telemetry studies is quite high as it needs proper equipment, trained labor, and staff for capture [4,11].

4. It is difficult to study tigers for years as their density is low and they live in remote areas of the forest [26]. One of the major challenges in telemetry studies is that it deals with the locational data of the species which can put the animal at risk. It is of utmost necessity to take proper care of data and it should be protected from unauthorized usage.

5. Another big concern over telemetry study is the hacking of radio collars. Poachers can hack the collar and can get the locational data of the animal, risking the animal for poaching [40].

6. Another challenge is the lack of fully advanced radio collars and cost. Many researchers complain about the premature expiry of the battery, collar failing, and incompatible data collection from the collar [11]. These issues suggest more technological advancements, training, and government contributions.

Telemetry studies pose challenges in data collection, integrating data, and data analysis [41]. The recent advances in telemetry devices allow data to be transmitted from the radio collar to the receiver, which is connected to the computer for data collection [42]. Some devices do not transfer the data to the receiver but store it in the telemetry device. Data received from these devices are unstructured data. Data integration is required to store and analyze the data. Integrating data means telemetry study could involve one or more species, one location, or multiple locations at the same time in the conducted study, hence data received from their collar need to be integrated for the storage [37,43]. Each device has its format of collecting the data, variables in the collected data can also vary according to the sensors used in the collar [30,33]. This makes data integration and data collection a challenging task to achieve. Telemetry devices’ error should also be taken into consideration by the researchers otherwise the inferences drawn from the data provided by these devices can be erroneous [44].