Bar-headed Geese | Photo: Vignesh Kamath / Research Matters
The bright red vent of a bird that’s surprisingly round as it sleeps is starkly visible among the branches. He has his head tucked under his 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 has been a big concern to the survival of these winged visitors. These problems are not unique to the Siberian crane – they are faced by many migratory birds the world over, in the past few decades.
The World Migratory Bird Day was established in 2006 by the United Nations, to be held in the second weekend of May annually. This year, the focus is on ‘Stopover sites: Helping birds along the way’. This theme is especially relevant when we stop to 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 they take amazingly lets them experience two summers in each migratory cycle. Each of these birds covers a distance of about 70,000 – 90,000 kilometres as they fly back and forth. While this particular bird covers most of its journey offshore, many birds are highly dependent on stopover sites to rest, feed and recuperate.
The Blyth’s reed warbler could comfortably fit in the palm of your hand. The bird doesn’t look particularly impressive, what with its plain brown and pale colour scheme. And yet, its migration starts from Eurasia, culminating in the scrub forests of south India. Along the way, it makes many stops in clearings and small patches of forests.
Hummingbirds are even smaller, and their migration is fascinating in its own right.
“Most hummingbirds weigh between 3 to 6 grams. And they have among the highest metabolic rates in the animal kingdom! So they use energy up really quickly, but they also have to remain light to fly efficiently”, informs Ms. Anusha Shankar, a Ph.D. student at Stony Brook University, USA.
One Rufus hummingbird actually flew more than 5600 km in 6 months. To be able to fly, the hummingbirds can’t store much fat; and they can’t always stop to feed while migrating, says Ms. Shankar. “Some hummingbirds can double their weight before migrating, going from 3 g to 6 g in just a few weeks”, 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 fishes, invertebrates and plants in abundance.
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 chicks. With ongoing intensive agriculture and alien trees being planted where native forests once stood, migration is made difficult for birds every passing season.
However, daylight and temperature cues are not the only reasons why birds migrate. In fact, 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, based in Coimbatore, is another organisation that participates 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, thanks to such tracking efforts.
But when migration is viewed as a behaviour that is displayed among a wide variety of 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 3 kg, migrates from places like the deserts of Rajasthan, over the Himalayas, at over 5000 m! 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”, wonders Ms. Shankar.
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’ve declared the 13th of May to be Endemic Bird Day. A large plethora of birds we see around us happen 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!