The importance of stopover habitats

Battling the odds

The importance of stopover habitats
The bright red vent of a bird that’s surprisingly round as it sleeps is starkly visible among the branches. It has its head tucked under the wing, and appears as a fluffy tuft of feathers at first glance. This is the Indian pitta, whose distinctive ‘wheeet-tieu’ call heralds dawn and dusk. These birds are winter visitors to peninsular India, and are one of the many species the subcontinent plays host to over the course of the year. The striking beauty of the Siberian crane, which flew to India all the way from Russia, used to be a reliable treat for birdwatchers to document. This bird, which has the longest migratory route among cranes, was an annual migrant to Keoladeo National Park in Rajasthan until the 1990s. Today, rampant destruction of habitat along its long route, and relentless poaching of the bird along the way have been two of the biggest concerns for the survival of these winged visitors. These problems are not unique to the Siberian crane. Many migratory birds from across the world have been facing  such odds in the past few decades.

Helping them along the way
The United Nations started to observe World Migratory Bird Day annually in the second weekend of May, since 2006. This year’s theme is ‘Stopover sites: Helping birds along the way’. This theme is especially relevant when we consider birds that fly across the world, quite literally. The Arctic tern, for example, flies from the Arctic, where it breeds, all the way to the Antarctic, almost every year. The convoluted route these birds take amazingly lets them experience two summers in each migratory cycle. These birds cover a distance of about 70,000 to 90,000 km as they fly back and forth — about six times the distance between Bengaluru to San Francisco (USA)!

While this particular bird covers most of its journey offshore, many birds are highly dependent on stopover sites to rest, feed and recuperate. One of them is the Blyth’s reed warbler — a small bird that could comfortably fit in the palm of your hand. The bird doesn’t look particularly impressive with its plain brown and pale colour scheme. Its migration starts from Eurasia, culminating in the scrub forests of South India. Along the way, it makes many stops in the clearings and small patches of forests.

Hummingbirds are even smaller, and their migration is fascinating in its own right. “Most hummingbirds weigh between three to six grams. They also have the highest metabolism of any homoeothermic animal! So they use up their energy really quickly, but they also have to remain light to fly efficiently,” informs Anusha Shankar, a PhD student at the Department of Ecology and Evolution in Stony Brook University, USA. One Rufous hummingbird actually flew more than 5,600 km in six months! To be able to fly, the hummingbirds can’t store much fat; and they can’t always stop to feed while migrating, says Anusha. “Some hummingbirds can double their weight before migrating,” she adds.

In many cases, these stopover sites could be marshes and wetlands, which are increasingly being taken over by human beings. Many species of birds use wetlands as breeding and nesting grounds, and aquatic birds cannot survive without stopping over at wetlands. Others might be dependent on these ecosystems for a wide variety of food sources, which includes fish, invertebrates and plants.

Climate change is also wreaking havoc with birds’ biological clocks. Birds typically sense the length of the day to determine whether it’s time to start their migration. Unfortunately, rising temperatures can give the wrong cues to start and end migration, and this means birds might not find food sources readily available when they arrive at their destination. In turn, this hinders their ability to raise a healthy brood of offsprings. With on-going intensive agriculture and alien trees being planted where native forests once stood, migration is made difficult for birds every passing season.

Reasons for bird migration
The reasons for bird migration have not been fully understood yet. Scientists are not sure how much of a role the genetic makeup of birds play, nor do we know why some birds of a population migrate and others don’t. The ‘how’ of migration is scarcely better understood. What we do know is that birds use celestial bodies like the sun and stars to make their way to their destination. The earth’s magnetic field has also been posited to play a role in directing birds on their journey.

In India, the Bombay Natural History Society (BNHS) partners with BirdLife International to coordinate conservation and research efforts in the country, with regard to birds. Salim Ali Centre for Ornithology and Natural History,  Coimbatore is another organisation involved in biodiversity conservation, with particular focus on birds. Migratory patterns of birds have been studied by ringing birds and using satellites to track their routes. Scientists have learned much about how species vary widely in the pattern of their migration due to such tracking efforts.

But when migration is viewed as a behaviour that is displayed among a wide variety of bird species, from tiny hummingbirds to large cranes, it puts things in a different perspective. “The demoiselle crane, which in terms of weight is the opposite of hummingbirds, at around three kg, migrates from places like the deserts of Rajasthan, over the Himalayas, at over 5,000 metres! What an amazing range of temperatures and altitudes they tolerate to achieve this — imagine if you had to do that without the protection of a plane,” says Anusha.

eBird India in coalition with Bird Count India conducts birding events throughout the year, in an attempt to introduce birding to interested amateurs, and to encourage professionals to keep contributing. For example, they have declared May 13 to be Endemic Bird Day. A large plethora of birds we see around us happens to be endemic to the Indian subcontinent. By recording their numbers and distribution, everyone can help in their conservation.

To start with, we can contribute tremendously by just placing a wide bowl of water in our backyards, so that birds can have some respite from the summer heat. Providing grains, fruits and nuts for them and making sure the area is safe only invites our feathered friends to take a break, before they continue on their long journey forward. And if you’re lucky, you might just catch some resident babblers frolicking about in your water bowl, making it their personal pool!

(The author is with Gubbi Labs, a Bengaluru-based research collective)

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