- A current monitoring examine has discovered that Montagu’s harriers keep away from crossing the Himalayas instantly on their migration route, as an alternative selecting an extended western detour that provides over 1,200 kilometres.
- This detour presents higher flying circumstances and essential stopover websites such because the Thar Desert and the Amu Darya floodplains for relaxation and refuelling.
- As these grasslands and open ecosystems are regularly disappearing, this finely tuned migratory path, and the species that rely on it, face an unsure future.
Yearly, Montagu’s harriers — slim, swish raptors with hanging wingspans — journey 1000’s of kilometres between their breeding grounds in Central Asia and their winter properties in India. However as an alternative of flying the shortest doable route, which matches by the Himalayas, these birds take an extended, winding path across the mountain vary which provides about 1,245 km to their journey.
A five-year satellite tv for pc monitoring examine now exhibits that this detour is each deliberate and surprisingly environment friendly. “Earlier monitoring research have discovered massive congregations of those species in Tal Chhapar in Rajasthan and Velavadar in Gujarat within the autumn season. Nonetheless, the monitoring knowledge revealed a stunning sample: after detouring westward to keep away from the Himalayas, the birds made a big eastward flip throughout Kazakhstan to achieve breeding websites close to Lakes Balkhash, Alakol, and Zaysan in japanese Kazakhstan, including appreciable distance to their general migration,” shares Arjun Kannan, lead creator of the examine, who’s affiliated with the Manipal Academy of Increased Schooling, and the SMS Basis Centre for Biodiversity and Conservation on the Ashoka Belief for Analysis in Ecology and the Setting (ATREE), Bengaluru.
A high-altitude impediment
Migrating birds typically face robust selections. Whereas shorter routes save time and vitality, they’ll additionally contain dangerous terrain, poor climate, or an absence of meals. Within the case of the Himalayas, averaging round 4,500 m in altitude, the risks are many: freezing temperatures, low oxygen, unstable winds, and restricted hovering circumstances for birds that depend on thermals to glide lengthy distances. These birds use rising columns of heat air (known as thermals) to achieve altitude and glide with minimal vitality, moderately than flapping their wings repeatedly.
For Montagu’s harriers specifically, a species that alternates between flapping and hovering flight, and infrequently flies above 4,000 m, making a direct flight throughout the Himalayas is sort of inconceivable. To learn the way they overcome this problem throughout migration, researchers fitted six harriers (4 males and two females) with light-weight satellite tv for pc tags, whereas one other 4 birds (one male and three females) have been fitted with GPS-GSM tags from 2016 to 2020.
Trapping the harriers was by far probably the most difficult a part of the examine. The researchers used mist nets and a decoy Indian eagle owl to lure the birds close to their roosting websites, as harriers are identified to mob potential predators like owls. “One season, we spent practically 60 days within the discipline, and managed to lure and tag only a single chook. In lots of circumstances, the harriers merely ignored the decoy. When just a few birds have been current, they have been particularly cautious and prevented the owl,” says Kannan. The info collected from 9 of them (one tag failed early) revealed a hanging sample: as an alternative of making an attempt a direct crossing, the birds migrated by way of a western detour, circumventing the Himalayas however crossing over the western stretches of the Hindu Kush vary. Remarkably, they adopted this identical detour each on their means south in autumn and on their return journey in spring.
Why the great distance is sensible
To know what made the birds selected this route, researchers used rules from optimum migration principle (Alerstam’s mannequin) to check the detour with a hypothetical straight-line path over the mountains. They analysed elevation, wind circumstances, and vegetation cowl (utilizing satellite-based NDVI, or “greenness”).
The detour route — about 1,245 km, or 27% longer than a direct flight — really turned out to be the smarter alternative and extra vitality environment friendly. The additional distance helped the birds keep away from the excessive, harsh circumstances of the Himalayas and as an alternative fly by simpler, safer terrain. “They’re avoiding an enormous mountain wall (the Himalayas), which stretches roughly 700 km. As an alternative, the detour takes them by open pure ecosystems, the place they could be utilizing a fly-and-forage technique,” says Kannan.
The examine recognized two key stopover websites — northwestern India’s Thar Desert, and the Amu Darya floodplains in Afghanistan. Due to seasonal rains, these areas supply bursts of vegetation and bug life, making them essential pit stops for the hungry raptors. “The Thar Desert seems particularly vital for refuelling. The harriers feed closely on resident grasshoppers, different bugs, and even perhaps lizards. After breeding season, many birds could be exhausted and plenty of could be inexperienced first-year juveniles. These refuelling websites will be important for his or her survival,” says Kannan.
Curiously, whereas wind patterns affect migration routes for a lot of chook species, it didn’t play a serious position for Montagu’s harriers. Though tailwinds generally helped velocity their journey, the birds additionally confronted headwinds or crosswinds throughout each legs of their journey. Nonetheless, the examine discovered that they constantly adopted the identical detour.
Why this issues for conservation
Montagu’s harriers are declining in India, and the explanations are nonetheless unclear. This new examine presents an vital clue: it maps, for the primary time, the complete migratory route of those birds. It reveals how their survival hinges on a string of places throughout their complete migration journey, not simply the place they breed or winter.
“Migratory birds thrive as a result of a community of interconnected websites throughout their full annual cycle the place they breed, refuel and winter. It’s embedded into their genetics. The lack of [these] websites can have carry-over results, ultimately resulting in a sluggish wipe-out of populations,” says Kannan.
The western circum-Himalayan hall utilized by Montagu’s harriers is especially fragile. A lot of it passes by open ecosystems that obtain little conservation consideration. The lack of grasslands and different pure habitats, particularly in areas just like the Thar Desert, might make this fastidiously developed migratory path unviable. Shifting additional west isn’t an alternate: it could make the already lengthy detour even longer, probably exceeding the birds’ vitality limits.
What’s extra, this hall kinds part of the Central Asian Flyway, a serious migration route utilized by many chook species. “A lot of raptors similar to steppe eagles, imperial eagles, Egyptian vultures, and noticed eagles is likely to be utilizing these routes. A handful of current monitoring research have proven this. However we solely have details about massive chook species. Many passerines, similar to larks, stonechats, and starlings, may also be utilizing this path to migrate out and in of the Indian subcontinent. Sadly, we don’t have correct knowledge on these smaller species as a result of an absence of monitoring research,” says Kannan.
Understanding the actions of those smaller passerines is essential, not only for their very own conservation, however as a result of they’re additionally prey for the bigger raptors. The examine’s authors hope their findings will information future conservation coverage and land-use planning throughout India and Central Asia. “Conservation is commonly hampered by lack of expertise of chook migration and motion at a superb scale. You will need to observe extra species alongside the Central Asian Flyway to establish these networks of related websites and work towards conserving not less than a few of them,” provides Kannan.
Learn extra: Understanding the elevational actions of Himalayan birds to enhance conservation efforts
Banner picture: Montagu’s harriers alternate between flapping and hovering flight, and infrequently fly above 4,000 m. Picture by Thalavaipandi.
