Animal movement ecology in India: insights from 2011–2021 and prospective for the future

Number of publications in the field of movement ecology from India

As expected, the number of publications (Figs. 1A and 1B) in the field of movement ecology from India has increased significantly over the years (Estimate = 0.082, P < 0.001, GLM: family=Poisson, link=log). This corresponds to the overall increase in the number of publications in the field due to advances in tools and technology—decreasing size and cost of tracking devices, the ability to collect finer-scaled spatio-temporal data and the development of appropriate and expansive statistical methods (Joo et al., 2018). The rapid increase in research publications in the field of movement ecology from India is also apparent when comparing the two different periods in which it is reviewed—Habib et al. (2014) reported 49 journal publications and reports between from 1985–2010 (26-year period) (Habib et al., 2014), and this study reports 82 between 2011–2021 (11-year period) (see Table S2).

Taxa tracked across publications

Amongst the research published in the past decade, mammals are the dominant taxa studied (76%; 62/82), followed by birds (13/82) and then reptiles (7/82) (Fig. 2A). Among mammals, the tiger, Panthera tigris alone accounted for 27% of the studies (22/82). Mammals were also the most dominant taxa tracked during the period from 1985–2010, and the tiger was the most dominant species among these as well. Due to this species bias, 78% of the animals tracked in the publications fall under the ‘Endangered’ or ‘Vulnerable’ threat categories of the International Union for Conservation of Nature (IUCN). However, among the 51 species tracked across all publications, 28 were in the ‘Endangered’ or ‘Vulnerable’ category while the rest were under ‘Least Concern’ or ‘Near Threatened’ (Fig. 2B). Only three of the 82 studies in this review tracked marine animals (Fig. 2C).

Number of publications across the country

The review reveals that movement ecology studies are unequally distributed across the country (Fig. 2E). Most studies come from parts of Central and Western India—Madhya Pradesh (17) Rajasthan (13) and Maharashtra (eight). Majority of the studies on the two big cats, tigers, and leopards (86%) also come from these states. Other states that dominate the publications are Karnataka (10), West Bengal (seven), Tamil Nadu (five) and Assam (five). Very few published studies have tracked species in the north of India specifically in the Himalayan regions—a trend that was also identified by Habib et al. (2014).

Methods for recording movement

The technology used for tracking animals in the studies included in this review fell into a few broad categories. Majority of studies (80%; 66/82) used Very High Frequency (VHF) radio transmitters, or GPS transmitters attached to animals for tracking movement (Fig. 2D). GPS transmitters (used in 37/82 studies) included devices that transmit spatial data to hand-held receivers, mobile networks, or satellites.

Non-invasive methods such as identifying individuals through visual encounters, through photographs from camera traps, or through genetic data from fur or fecal samples formed the rest of the movement studies (16/82). Non-invasive methods use unique intrinsic markers of individuals, such as coat patterns and genetic information for infer movement and displacement across the landscape (Hobson & Ryan Norris, 2008). For example, images from camera traps were used to identify and estimate the home ranges of leopards (Kumbhojkar et al., 2020), dispersal distance of tigers (Singh et al., 2013) and space acquisition of vacated sites in tigers (Singh et al., 2020). Genetic evidence from tigers have been crucial to infer movement (Reddy et al., 2012) and dispersal patterns (Gour et al., 2013), and to determine whether tiger populations were connected across human-modified landscapes in central India (Joshi et al., 2013). Studies on the home range of primates have used visual identification to record movement of the groups. For example, the home range of Eastern Hoolock Gibbon Hoolock leuconedys (Sarma & Kumar, 2016), Lion-tailed macaques Macaca Silenus (Erinjery, Kavana & Singh, 2015; Santhosh et al., 2015) and Rhesus macaque Macaca mulatta (Sengupta, McConkey & Radhakrishna, 2015) were recorded by observers using hand-held GPS devices.

Research goals across publications

Potential research directions for India in the field of movement ecology

Given the rapid growth and current state of the field of movement ecology in India, the possibility for generating new knowledge is abundant. This literature review, spanning movement ecology research in India over the last 11 years, shows the disproportionate focus on some taxa (e.g., tigers) and some metrics of movement (e.g., home range). We take this opportunity to call for a broadening of the scope of movement ecology studies, bringing forth the most urgent needs of the field. We also seek to identify where the unique biogeography and biodiversity of India can provide interesting opportunities for research in this field (Table 1).

Table 1:

Prospective research directions in the field of movement ecology and potential questions that can be investigated in India.

No.	Research topics	Potential questions to address
1.	Tracking species across seasons and years	How do animals in different biogeographic zones track climatic changes?
2.	Tracking species across different landscapes	How generalised are species responses, or are movement strategies driven mainly by the immediate environment?
3.	Tracking many individuals	How do conspecific interactions influence individual movement decisions?
4.	Tracking species outside protected areas	What are the strategies and limitations that enable animals to survive with anthropogenic alterations to their environment?
5.	Tracking diverse taxa in the same area	How do species traits individually or in combination affect the movement decisions of a taxa?
6.	Tracking smaller taxa	How do smaller animals make movement decisions, from daily foraging across habitats to long-distance migration across continents?
7.	Tracking marine and freshwater taxa	What are the migratory patterns of marine taxa? How do humans impact their movement? Are there eco-sensitive areas that need additional protection?
8.	Tracking animals to reduce human-wildlife conflict	Are there patterns of animal movement that enable proactive and anticipatory action to mitigate human-wildlife conflict?
9.	Tracking animals and ecological processes	How does animal movement impact various ecological processes, such as seed dispersal or pollination? How does global change affect these crucial functions?
10.	Tracking animals with different sensors	What environmental variables best track changing conditions and how do they influence animal movement?

DOI: 10.7717/peerj.14401/table-1

1. There is considerable insight that can be gained from tracking species over long periods of time, such as multiple seasons and years. Movement decisions of animals are driven in large part by distribution and availability of resources, which change with seasonality (Abrahms et al., 2021). Seasonality in India is influenced by various spatially explicit factors. Parts of India receive the bulk of the monsoon rains and these regions can be divided into the wet and dry seasons. Southern parts of the country are tropical, while the northern parts are sub-tropical to temperate. Some parts of India are also projected to face greater effects of climate change than others, compounding the impacts on environments. Understanding whether and in what ways animals can respond to natural and human-induced climatic shifts across years, through long-term studies, will enable us to determine how quickly animals, resources and their drivers can respond.

2. Patterns of resource distribution varies across landscapes, and thus the same species in different environments are expected to differ in their movement decisions (Shepard et al., 2013). Monitoring animals across different landscapes enables us to infer the significant drivers of movement and their variation, to determine how much of movement strategies are inherent to the species, and how much are driven by local environmental conditions. From evergreen forests in the southwest and northeast to arid deserts in the west and snow-clad mountains in the north, India possesses diverse landscapes. Each landscape consists of species adapted to the region, but they also share some species. Thus, tracking the same species in different environments across seasons, is a powerful approach, especially in the context of global change.

3. The movement strategies of individuals are not only driven by environmental conditions but are also influenced by interactions with conspecifics. Simultaneous tracking of many interacting individuals in an area will provide insights into how social interactions influence decision-making and space-use patterns (reviewed in Westley et al., 2018). Until now, most animal tracking in India has been confined to understanding the extent of space-use patterns of a few individuals of a species. Multiple individuals are rarely tracked together, and thus, the contribution of group members or conspecifics to movement decisions is an exciting research direction.

4. Natural spaces for animals are reducing (Hirt et al., 2021) and animals are increasingly forced to utilise landscapes modified by humans. Many species might curtail their movement altogether in these altered landscapes (Tucker et al., 2018). Such impedance to movement may affect the animal’s dispersal (Chazdon et al., 2009) and in the long term, species distribution. India has a population of ~1.35 billion people spread across urban and rural areas, and thus, human-animal encounter rates are high. Dedicated wildlife habitats in India are fragmented and are flanked by either residential, agricultural, and/or industrial developments. Tracking species outside protected areas will generate a stronger understanding of the strategies and constraints that enable animals to survive in an era of global change, which includes a moving animal being able to tackle both climate change and land transformation (Sage, 2019).

5. The movement behaviours and strategies of animals are influenced by multiple intrinsic factors, such as size (Jetz et al., 2004), morphology (Börger et al., 2020), and cognitive ability (Kashetsky, Avgar & Dukas, 2021). To make generalizable predictions of animal movement that examine the effects of intrinsic differences while controlling for extrinsic or environmental factors (Nathan et al., 2008), tracking different kinds of taxa in the same area is a powerful approach. India hosts ~400 mammals, ~1,400 birds, and ~600 reptiles and amphibian, and thus the opportunities to track diverse taxa that play key functional roles within an ecosystem is immense.

6. Obtaining movement data from smaller vertebrates and invertebrates is a challenge, given that bio-loggers must be miniature and weigh a fraction of the animal’s weight. Animals as small as bumblebees (200–450 mg; Hagen, Wikelski & Kissling, 2011) and butterflies (300–700 mg; Fisher, Adelman & Bradbury, 2020), have been tracked to determine flight paths, space use, and migration patterns. Other technological advances with projects such as ICARUS (Belyaev et al., 2020; Jetz et al., 2022) and wireless network sensors (Ripperger et al., 2020) have made the fine-scale tracking of numerous small taxa more feasible today. Given that the technology to track the movement of smaller animals is rapidly advancing, future studies that track the movement of insects, smaller mammals, and birds in India, will provide key insights on species that have not been tracked before.

7. The marine ecosystem offers an opportunity to address many key ecological questions—from the influence of memory or learning, and social interactions, to prey distribution, and the impact of global change (Hays et al., 2016). Marine animals with sensors can potentially act as sentinels and record environmental variables in regions in the ocean not commonly sampled, which will allow us to better understand climate and ocean variability (McMahon et al., 2021). With a coastline of ~7,500 km, there is immense potential to track the movement of various marine animals to provide relevant information for the conservation of species and ecologically sensitive marine zones of India.

8. Animal tracking has a direct application in regions with human-wildlife conflict. Tracking animals is not only useful for understanding animal movement, but it helps reduce conflict by sending early warning signals to alert people to the location of the animal so they can take pre-emptive action (Venkataraman et al., 2005). In India, animal tracking studies on large carnivores (such as tigers and leopards), or herbivores (such as elephants, wild pigs Sus scrofa, and nilgai Boselaphus tragocamelus) can help mitigate direct and indirect human-wildlife conflict. Animal tracking information in combination with early warning signal alerts, can potentially prevent human deaths and infrastructure damages (Kumar & Raghunathan, 2014), reduce agricultural crop damages, and avoid railway collisions of wildlife (Datta et al., 2016). Such studies can also determine barriers and corridors to movement (Joshi et al., 2013). Additionally, citizen-science information of animal locations would be a valuable complement to telemetry data, enabling a better understanding of animal movement decisions, especially of species prone to human-wildlife conflict.

9. Animal tracking studies are crucial for understanding how movement affects ecosystem processes in a landscape. Movement of frugivorous birds (Ramaswami et al., 2016; Naniwadekar et al., 2019, 2021) and mammals (Sekar, Lee & Sukumar, 2015) have implications for where plants species disperse their seeds and their future survival. Loss of this dispersal service will directly affect the capacity of plant species to respond to changing climatic conditions (Mokany, Prasad & Westcott, 2014). Landscape fragmentation also affects the movement of bees and butterflies, and therefore impacts plant pollination (Hadley & Betts, 2012). Additionally, megaherbivores like an elephant trampling through a forest can engineer ecosystems by changing vegetation patterns (Haynes, 2012). Given the latest advances in animal tracking devices (see (6) and (10) in this section) it is now possible to study how animal movement influences ecological processes in different climatic regions across India.

10. Technological advances have spearheaded the field of movement ecology over the last two decades in ways that enable the tracking of species as well as their environments (Kays et al., 2015; Sherub et al., 2017). Innovations in technology, methods to analyse big data (Thums et al., 2018) and sensors that record different kinds of information (Sherub et al., 2017), have all expanded the scope to ask newer ecological questions related to the movement decisions of animals. This also allows for the standardisation of bio-logging devices for conservation management use (Sequeira et al., 2021). Additionally, collared animals themselves can now be used to collect fine-scaled data on the environments they utilise (Börger et al., 2020; Thaker et al., 2019). With the available tracking technologies, it’s now possible to understand and mitigate the impacts of global change, a direction that India is primed to pursue. Going beyond the focus of individual species or specific geographic regions in India, we can now track animal movement with environmental sensors that also track temperature, wind pressure, sound, and several other key parameters.

Limitations to this review and to the growth of movement ecology in India

To the best of our knowledge, we have conducted an exhaustive search of animal movement studies carried out in India over the last 11 years. We acknowledge that some studies may have been missed, especially if these were not published in peer-reviewed journals listed on SCOPUS or Google Scholar. For example, many state forest departments collar and track species of interest for general monitoring and to mitigate wildlife conflict. These data are typically not available for public access or published in scientific journals. Additionally, studies with low sample sizes are more likely summarised in reports to granting agencies or forest departments, which are also not accessible. Therefore, the taxa that we identify as having been collared or tagged over the last decade is likely to be missing species. There has, however, been a new push to tagging and tracking animals and many of these initiatives have been announced in newspapers or social media (see Table S3), and so the field of movement ecology in India is set to see a rapid period of growth. Overall, our review effectively captures the general trends and approaches in the field of movement ecology in the country and has allowed us to identify research gaps and future research directions. Some of the potential research directions that we propose, for example monitoring animal movement in human modified landscapes to reduce wildlife conflict, have already been initiated. Similarly, the tagging of migratory species, such as the endangered Great Indian Bustard, is also ongoing and is of urgent national importance. Although not included here, these studies reflect new and necessary directions for this field.

Among the shortcomings identified in the previous review from India, by Habib et al. (2014), a lack of animal tracking studies from the northern part of India, an emphasis on certain research goals (e.g., home-ranges and habitat selection), and the need for a centralised system to ease the permission to capture and collar animals, were highlighted. While there appears to be a positive trend to address some of these issues, most of the deficiencies still exist. One way to address these gaps is by forming a biologging group/forum/conclave that brings together both experts and stakeholders from various research institutions, state forest departments, and conservation organizations to share information, technology, and collaborate on future projects across the county. Collaborations between research institutions and government agencies might help reduce the difficulties in obtaining research permits for capturing and collaring animals and may directly facilitate conservation management goals. Additionally, we urge researchers from India to adopt an open data policy whenever possible, which would involve uploading animal movement data, both published and ongoing, to global databases, such as Movebank (Kays et al., 2022). By joining the global initiative of movement ecology, researchers from India have larger opportunities to collaborate on global-level analyses of animal movement. In the rapidly changing Anthropocene, where anthropogenic disturbance and climatic change are irreversibly altering the Earth, collaborative global approaches to tag, track, and understand animal movements is essential to understand species responses and to mitigate impacts on crucial ecosystem functions.