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On the tiger trails: Leopard occupancy decline and leopard interaction with tigers in the forested habitat across the Terai Arc Landscape of Nepal

Better conservation planning requires updated information about leopard distribution to
prioritize and allocate limited resources available. The long-term persistence of leopards
and sympatric tigers can be compromised by linear infrastructure development such as
roads that fragment habitat. We used detection and non-detection data collected along
walking search paths (~4140 km) in 96 grid cells (each cell 15 km by 15 km) spread across
potential habitat (~13,845 km2) in the Terai Arc Landscape, Nepal. Multi-season occupancy
models allowed us to make both spatial and temporal inferences between two surveys in
2009 and 2013, based on ecologically relevant covariates recorded in the field or remotely
sensed. Additionally, we used 2013 data to make inferences on co-occurrence between
tigers and leopards at the landscape level. We found the additive model containing
deforestation and district roads negatively influenced leopard detection across the landscape.
Although weak, we found anthropogenic factors such as extent of deforestation
(decrease in forest cover) negatively affected leopard occupancy. Road abundance, especially
for the east-west highway and district roads, also negatively (but weakly) influenced
leopard occupancy. We found substantially lower occupancy in the year 2013 (0.59 (SE
0.06)) than in 2009 (0.86 (SE 0.04)). Tigers and leopards co-occurred across the landscape
based on the species interaction factor (SIF) estimated at 1.47 (0.13) but the amount of
available habitat and the prey index mediated co-occurrence. The SIF decreased as habitat
availability increased, reaching independence at large habitat patches, but leopard occupancy
declined in sites with tigers, primarily in large patches. The prey index was substantially
lower outside of protected areas and leopards and tigers co-occurred more
strongly in small patches and at low prey indices, indicating potential attraction to the
same areas when prey is scarce. Mitigation measures should focus on preventing loss of critical leopard, tiger, and prey habitat through appropriate wildlife-friendly underpasses
and avoiding such habitat when building infrastructure. Leopard conservation has received
lower priority than tigers, but our metrics show a large decline in leopard occupancy, thus
conservation planning to reverse this decline should focus on measures to facilitate
human-leopard coexistence to ensure leopard persistence across the landscape.