Wintering Raptors Survey in Lowlands of Nepal
The lowland of Nepal is largely dominated by farmlands, grasslands and dense forests, and with a comparatively warm climate even in the winter, provides important habitat for both resident and migrant birds including several species of raptors. Environmental variables within the wintering areas must be ideal to provide sufficient amount of energy compensation to costs associated with predation, competition and inclement weather to migratory raptors (Moore et al., 1995; Moore and Aborn, 2000). Habitat qualities have important consequences for survival and are important in explaining the population size and dynamics of migrants (Probst and Hayes, 1987; Porneluzi et al., 1993; Holmes et al., 1996). During the onset of winter in the northern hemisphere, millions of raptors travel to the warmer area to escape the harsh weather (Kerlinger, 1989), and birds of prey from Northern Asia leave their breeding grounds (Tibetan Plateau and Northern Asia) to move further south, possibly towards the lowlands of Nepal, India and even as far as Africa. Subedi et al. (2014) counted approximately 14,000 individuals of migrating raptors annually during autumn migration count, with 37 species moving to unknown wintering grounds. Previous observation in lowland area of Nepal shows several species of raptors, especially large number of near threatened Himalayan vulture (Gyps himalayensis), use the area as a part of wintering ground, however no database exists to quantify the species and total number of individuals that use the lowland area of Nepal during winter (Himalayan Nature, 2014).
Thus, this study was started in 2016 to establish a baseline to quantify species and number of both migrant and resident raptors during the wintertime in the lowlands of Nepal, as well as to assess their relationship with the habitat. This in turn will contribute towards establishing status and population trend of migratory and resident raptors in Nepal’s lowlands.
The wintering raptors survey was done for the first time in Nepal, and surveys were conducted during December 2016 and March 2017 to coincide with migration periods of raptors. The surveys have identified several threatened species including the critically endangered White-rumped vulture and Red-headed vulture. Field researchers started the study from the Eastern border (Mechi Bridge) and conducted surveys along the main east-west highway, as well as along several side routes, all the way to the Western border (Ghaddachauki).
The diversity was found to be quite high, with a total of 36 different raptor species observed. Individual raptor count totaled to 1649, with 1044 individuals recorded during the winter count, and 605 during the spring count. This baseline data will be important when conducting future surveys of migrating and resident raptors across the Terai lowlands. Winter survey accounted for the most number of raptor sightings and one reason for this may be that by the time the spring count began, the birds may have already migrated back to their breeding grounds. There was a higher occurrence of birds along the Lauki – Kadmaha section in the main highway and Jeetpur – Bhumai side road transect. While it could be that raptors are favouring valleys with warmer climate, this requires an in depth study. The wintering site for raptors was found to be highly dependent on habitat type, with higher occurrence in agricultural lands and lower in riverine areas with no agricultural lands in the vicinity.
There is the possibility of direct and indirect threats to raptors through pesticide spray and consumption of prey that have absorbed agricultural pesticides. This is also an area that warrants further research and as such, conclusions cannot be made regarding the reasons for habitat selection of wintering raptors in the lowlands of Nepal. Conservation awareness workshops may need to be held across the lowlands targeting the use of pesticides and its effects on the raptor population.
This survey has opened up many research and conservation areas to focus on in future studies, by providing data on wintering hotspots and habitat preferences. Continue monitoring will be undertaken to establish raptor population trend.