Despite the high altitudes and harsh winters, the Himalayas are a global biodiversity hotspot, home to 10% of the world’s bird species. But expanding human populations in the Himalayas have resulted in widespread conversion of intact forests into agricultural lands for crop cultivation and pastures for livestock grazing, threatening biodiversity.
Yet, the region is rich in biodiversity and now researchers have found that these agricultural lands are teeming with large numbers and species of birds in the winter as well as in the breeding season (summer). However, their study also revealed many bird species rely exclusively on primary forests to breed.
These findings suggest “we need to both protect intact primary forest and minimise pasture expansion,” said Paul Elsen, lead author of the study and research fellow at the University of California, Berkeley.
“This is possibly the first systematic study of the impacts of land-use change on avifauna in the Himalayan region,” said Ghazala Shahabuddin, a scientist at the Centre for Ecology, Development and Research, a Dehradun-headquartered not-for-profit organisation, who was not involved in the study. “It is significant because the Himalayas are important for biodiversity conservation, harbouring approximately 80% of the bird fauna of India.”
Elsen has been studying Himalayan birds over the past six years and in an earlier 2017 study, his team was surprised to find that agricultural lands in the region harboured a high number of species, at high densities, in the winter. But the team wondered if this changes in the breeding season, because Himalayan birds are altitudinal migrants. Widely fluctuating temperatures in the region affect food supplies and this in turn affects how birds use different habitats.
“They breed at high elevations in the forest and migrate to lower elevations in winter” where agriculture is more prevalent, explained Elsen. Moreover, “species have very different requirements during the breeding season; they need to establish territories, attract mates, build nests, feed their young,” he added.
To account for seasonal migrations, Elsen’s team surveyed birds along an elevation belt of 2,000-2,700 metres in primary forest in the Great Himalayan National Park situated in Himachal Pradesh and the neighbouring agricultural lands during the breeding season and in the winter. They focused on how the bird community changes in composition during the different seasons including their abundances, species richness and species-specific population trends.
The team conducted surveys along a gradient of land-use intensity going from undisturbed primary forests to forest-agriculture mosaic, characterised by small agricultural plots and large native trees where villagers engage in selective logging for timber; mixed-agriculture mosaic, consisting of terraced agriculture with dozens of crops and small shrubs; and pastures used for livestock grazing.
Agricultural lands serve as a winter refuge
The team found that the agricultural lands were not only important in the winter, but also during the breeding period. Both forest-agriculture and mixed-agricultural mosaics harboured higher abundances and species of birds in both seasons compared to pasture and primary forest.
Unexpectedly, pastures had higher bird abundances and species in the winter than in primary forest, but species richness was higher in the primary forests during the breeding season.
Trevor Price, a professor at the University of Chicago, who was not involved in the study, said that this is an important paper demonstrating that pasture/agricultural land “is not all bad, in that some forest species can utilise it in the winter, and other species are pretty well confined to it.” He added that a higher species richness in agricultural lands than in pure pasture and pure forests “is a common finding in other studies, likely resulting from mixing of species adapted to different habitats.”
Elsen suspects that birds flock to agricultural lands because they have greater food availability than forests in the winter. Price agrees, stating that deciduous forest trees lose their leaves in the winter resulting in few food resources. “In more open areas, shrubs maintain leaf in this elevation belt, which can be exploited by insects and hence the bird species that feed on them,” he explained.
In a 2000 study, Price’s team found that the northern range of Hume’s leaf warbler, a species that winters in India, is limited because of the loss of arthropods due to leaf loss from deciduous trees. Agricultural lands feature shrubs, he added, which are more “likely to carry fruits and open land seeds from grasses.”
But why was diversity high in the agricultural lands during the breeding season when food availability should not be a limitation in the forests?
“It could be due to species simply moving throughout the environment and being observed in agriculture, though they would preferentially use the forest,” said Elsen.
Many species prefer primary forest to breed
The team also found evidence showing that primary forests are important during the breeding season because many birds found on agricultural lands in the winter relied on forests in the breeding season with some that exclusively used forests. More than twice the proportion of species found in primary forest were absent or declined in forest-agriculture during the breeding season, compared to winter. Although all land-use types hosted unique species, primary forests held 20 unique species in the breeding season—five times more than in the winter.
Additionally, species that were found in primary forests during the breeding season were most abundant in the intact forests, whereas species observed in primary forests in the winter were found in equal or greater abundances in the agricultural lands during winter.
Price noted that “other species that are found in disturbed areas may not persist if they were not supported by a population that breeds in primary forest nearby.” He stressed, “This is an important point: if we lose primary forest we may lose not only the 20 species but others that superficially can persist outside of primary forest as well.”
He pointed out that a similar 2011 study conducted in the lowland forests of Uttarakhand, found that 80 percent of the 95 forest-dwelling species were rarely seen outside of the forests.
Preserve primary forests, limit pasture expansion
The results suggest, “protecting forest is critical for breeding birds, as most species depend on these forests to maintain high abundances,” said Elsen. “Protection, in this case, could be in the more traditional sense, such as a national park or wildlife sanctuary.”
This strategy should be complemented by preventing the conversion of forest-agriculture and mixed agriculture to pasture, which can harm both breeding and wintering birds. He notes that the few species that were unique to pasture are common globally. Limiting conversion to pasture may be achieved through community-based programs that provide incentives to local communities to maintain forest cover.
We need to focus on preserving forests, said Price, because “pasture and agriculture are hardly threatened habitats.” He refers to the Uttarakhand forest study, which showed that many tree species in northern India are only found in primary forests.
The findings of this study warrant re-evaluating the impacts of large-scale road-widening and dam construction which have been recently begun in Western Himalayas, added Shahabuddin, noting that these activities can further threaten species such as the Himalayan monal and the Western tragopan. Interestingly, the researchers observed the former only in primary forests during the breeding season.
While this conservation strategy applies to western Himalayan birds, it may not work for species in the eastern Himalayas, cautioned Elsen. As a result, he suggests expanding similar studies to a larger area in the region and covering more species to optimise conservation strategies.
This article first appeared on Mongabay.
