Text by: Neha Jain
Wildlife biologists have reported the longest dispersal and subsequent home establishment of an 18-month-old female tiger 99-kilometres away from her home site at Panna Tiger Reserve in Madhya Pradesh. The sub-adult tigress is a second-generation female among a population of seven tigers that were reintroduced in the reserve from 2009 to 2015 after the native population was lost to poaching.
Tiger habitats in India are fragmented and highly mosaic, often interspersed with human-dominated landscapes. Therefore, the movement or dispersal of tigers is important to establish new territory and for survival. Most tiger dispersals recorded worldwide have been traversed by males in response to competition for mates or resources or both whereas females tend to stay in their area of birth.
“Long-distance dispersals are rare in female tigers,” says Mriganka Shekhar Sarkar, scientist at the North East Regional Centre, G.B. Pant National Institute of Himalayan Environment, and an author of the report. The movement of the tigress, known as P213-22, is “a rare event and an important milestone towards a greater understanding of tiger biology.”
While such events are rare, “it is possible that habitat fragmentation and increases in population size due to successful conservation may impose conditions that change dispersal behaviour and even aspects of territoriality,” adds co-author Robert John Chandran, associate professor at the Indian Institute of Science Education and Research, Kolkata.
“Our study suggests that female dispersal could contribute to gene flow and range expansion in tiger populations, which could be important in the current scenario of fragmented habitats but with increasing tiger numbers due to successful conservation efforts.”
Chandran adds the Madhya Pradesh Forest Department is still tracking P213-22 on the ground using very high-frequency radiotelemetry and opportunistic camera trapping. “The tigress is still doing well in the region, Sarkar says, adding that she “produced a litter of five cubs, of which three have expired.” She is rearing the remaining two cubs.
Offspring of tigress P213-22. The dispersal of P213-22 is a rare event and an important milestone towards a greater understanding of tiger biology. Photo: Satna Forest Division
Cover Photo: Camera trap image of tigress P213-22. Cover Photo: Satna Forest Division
Stepping stone habitats key to dispersal
A team of field staff and researchers tracked the locations and movement patterns of P213-22, which was fitted with a radio collar, over a period of two years from 2015. They used 743 locations during the dispersal period which lasted from October 2015 to December 2015 and was characterised by the highest rates of movement. During the final settled period, which consists of home-range patrolling, 340 locations were considered from June 2017 to September 2017.
Over a period of 78 days, P213-22 traversed a linear and cumulative displacement of 99 km and 340 km respectively. Travelling mostly at night, P213-22 passed through forest patches near water channels and agricultural fields while avoiding human settlements. During the dispersal event, P213-22 traversed an area of 2082 square kilometres, which included 19 ‘stepping stone’ patches of habitat.
‘Stepping stones’ are small good-quality patches of habitat that can provide temporary refuge for resting and foraging during dispersal, explains Sarkar. They can greatly improve the chances of successful long-distance dispersal events, Chandran adds. In the stepping stones, which were mostly within territorial forests of North Panna and Satna Forest Divisions, the movement of P213-22 slowed down (0.15m/s) compared with the movement outside where the rate was almost 6-fold higher (0.94m/s).
According to Chandran, recognising the role of these small patches as ‘stepping stones’ pave the way for their conservation. “A metapopulation approach to conserving such species could integrate stepping stone habitats as a key component in identifying and conserving dispersal corridors for large mammals,” he suggests.
Pranav Chanchani, national lead for tiger conservation at World Wide Fund for Nature-India (WWF-India), says that this case casts light on how “small tracts of forests within the matrix beyond protected areas can serve as vital stepping stones—where tigers can shelter—enabling them to successfully disperse through otherwise narrow and disturbed corridors.”
Chanchani, who was not connected to the study, stresses the “importance of prioritising conservation initiatives beyond protected areas — including within corridors, agricultural areas and reserve forests — all of which are essential to sustain tiger meta-populations and enable range expansion.”
Provided there is structural connectivity, Chanchani says wildlife corridors will enable dispersal events similar to that of tigress P213-22. “Such movements often go unrecorded,” he says, “but they may well hold the key to tiger recovery and persistence in fragmented landscapes.”
Cubs of P213-22. In her new home, which consists of a non-protected area, the tigress had mated and is rearing two cubs. Photo: Satna Forest Division
Railway line near new home
The new home of the tigress lies in a non-protected area near Ranipur Wildlife Sanctuary, which is concerning, says Sarkar. A railway track passes through the major corridor that connects Panna Tiger Reserve and Ranipur Wildlife Sanctuary. “There have been incidents of tiger mortality due to collision with trains on this rail track.” Consequently, the authors recommend increasing surveillance around this railway line. “We suggest putting up fences on both sides of the rail line and constructing a few wildlife passes underneath the rail line.”
Located adjacent to Ranipur Wildlife Sanctuary is the Madhya Pradesh forest ranges of Majhgawan, Barundha, Singhpur, Chitrakoot, Simariya, Sirmor, and Atrela, in the Satna and Rewa forest divisions. These areas, Sarkar says, provide a good forested ecosystem for the conservation of tigers. “Our suggestion is to upgrade the legal status of this entire forested region to a conservation reserve. This would ensure a better management regime for tiger conservation in this region.”
Having analysed the patterns of space use by P213-22, the researchers have identified locations where the forest department must step up surveillance and allocate additional resources for the conservation of tigers. “Conserving the indicated areas would facilitate the dispersal of other male and female tigers between Panna Tiger Reserve and Ranipur Wildlife Sanctuary,” says co-author Rajasekhar Niyogi who is a doctoral student at the Indian Institute of Science Education and Research, Kolkata.
“Dispersal events like these may become untenable,” Chanchani warns, “unless connectivity conservation tenets are systemically embedded within land-use planning and infrastructure projects.”
Chandran foresees more tigers, both male and female, dispersing out of habitats in search of new territories, reflecting in part the success of conservation. “Such gains can only be consolidated if range expansion through dispersal and the colonisation of new sites (typically erstwhile habitats) is possible.”
This story was first published in Mongabay India
