By Mousumi Ghosh (with inputs from Umesh Srinivasan)

Tips for Identification

If you’re keen to start leaf warbler watching, you just need an ear for it! You can start with the commonly encountered leaf warbler species in our backyard like Hume’s Warbler (in North India) and Greenish Warbler (in South India) and fortunately, both are extremely vocal. Anytime I want to hear a Hume’s Warbler in winter here in Dehradun, I just have to strain my ears a bit and sure enough I can hear one (yes, it’s that common during winter in North India). Both are territorial in winter and call incessantly guarding their precious trees from the canopy. So, let’s get acquainted with some of the commoner species which visit us in the plains in winter (Here is an illustration to help you with some of the terms commonly used while describing warblers):

Hume’s Warbler (Phylloscopus humei):  One of the commonest leaf warblers, it has an overall dull colour with greenish upperparts and off-white underparts. Other features include a long supercilium, weak/absent crown-stripe, prominently pale tertial edges, no white margins to the tail, one prominent pale wing bar (just a faint vestige of the second wing bar may be visible). The darker legs and lower mandibles are diagnostic. Hume’s is among the smaller of leaf warblers; it breeds near the tree-line and is partial to birch forests in the summer. In the winter it is one of the commonest species found all over the plains of North India. It’s solitary in winter and calls incessantly from the crowns of trees. Call: A repeated, disyllabic ringing tiss-yip, buzzy wheezing tzzzeeeeeu, often given interspersed with calls.

Greenish Warbler (Phylloscopus trochiloides): A common winter migrant in peninsular India, it is one of the larger leaf warblers. It has greyish-green upper parts and off-white underparts. Absence of coronal stripe, yellowish-white supercilium and a single wing bar are other features which help distinguish this species.

During the breeding season, Greenish Warbler occurs close to the tree-line in mixed-conifer forests and rhododendrons. In winter, it is territorial and partial to the canopy, from the top of which it calls incessantly to defend its precious territory. Call:  a disyllabic tisswit or chiswee.

Lemon-rumped Warbler (Phylloscopus chloronotus): This tiny little leaf warbler gets its name from its pale yellowish rump which is frequently exposed as it hovers at the edge of leaves to pick arthropod prey. It’s a rather active bird with olive green upperparts, whitish underparts, dark bill and pale legs. The head is rather distinctive with a prominent pale yellow crown stripe, a broad yellowish supercilium and a very dark eye-stripe which broadens behind the eye and hooks under the ear coverts. Typically two yellowish wing bars are visible, the lower one being larger and more prominent. This species is an altitudinal migrant, spending the summer in the mixed coniferous, oak and rhododendron forests and retreating to the foothills in winter where it joins mixed-species flocks to forage mostly in the mid-canopy and undergrowth. More than two may be part of the same flock, daintily hovering around the vegetation and is an absolute treat to watch! Call: A high-pitched tsip or uist.

Apart from the above there are a number of other species of Phylloscopus warbler that can be observed in the Indian subcontinent. Most of these species migrate over long distances to winter in the Indian plains and peninsular India, some show an altitudinal migration, and a couple of them are resident throughout the year. Here is a very handy key for their visual identification compiled by Umesh Srinivasan.

This concludes our three-part series on Phylloscopus warblers. We hope that these articles helped you in identifying the main species in this difficult group and also provided interesting information about the ecology of leaf warblers. We’d like to know if you liked this series and if you’d like us to run more such articles in the future on the MigrantWatch blog. Please do send in your comments and feedback at mw@migrantwatch.in. 

You can read Part I and Part II in this series of articles on leaf warblers.

Here we present the year-wise arrival pattern of one of our most observed species – the Greenish Warbler.

As in our earlier illustrations, each sighting is shown as a vertical black line.

The above graphic shows that Greenish Warblers start their southward migration into the Indian subcontinent in late August. They stay on till early summer and by May almost all of them return to their breeding grounds in the Himalayas and beyond.

To look at all the Greenish Warbler sightings on MigrantWatch please click here. You may also want to look at our series on Phylloscopus warblers here.

By Mousumi Ghosh
Read Part I in this series of articles on leaf warblers

Wintering Season

To most of us, Phylloscopus leaf warblers belong to just one size category: tiny! And confusing. Every winter, these diminutive and inconspicuous birds envelope the subcontinent in a wave, migrating thousands of kilometres south from their breeding grounds in the Himalayas and beyond. Migrating long distances takes a lot of energy, particularly for smaller species. Small differences in body weights among species make a huge difference in deciding how far they have to travel for wintering. Small-sized warblers are geared to feed on small insects, which are available in good quantities right from the Himalayan foothills all the way down south. The larger Phylloscopus warblers (like Large-billed, Greenish, and Western-crowned) do not have it so easy, as their preferred food – large insects – are available in adequate supply only further south. Hence, in the wintering season smaller species don’t travel very far, with their southern limit being either the sub-Himalayan foothills (e.g. Lemon-rumped Warbler) or mostly up to Central India (e.g. Hume’s Warbler), where wintering ranges of larger species begin. In contrast, larger species  (e.g. Greenish and Western Crowned Warblers) travel farther south and all way to southern India and Sri Lanka.

A great deal of knowledge about the wintering ecology of Greenish Warblers has emerged from Madhusudan Katti’s work in the Kalakkad-Mundanthurai forests of Tamil Nadu. He found that individual birds, quite remarkably,  come back to the same wintering territory year after year!  Also, in years of scanty rainfall and limited food the birds were unable to eat enough to moult in time for their long journey back to their breeding sites. This shows how conditions in their wintering habitats may influence whether birds are able to make it back to breed; and this has obvious implications for the size of the population.

Several parallels exist between the way these birds breed and winter. For example, the species which breed on “top of the mountains” (Hume’s  and Greenish Warblers) spend the winter on “top of the trees”. Interestingly, while these two species are territorial in winter (both males and females defend territories), others, like the Western-crowned and Lemon-rumped Warblers, join mixed-species flocks. Although most species spend their breeding and wintering seasons in drastically different forests, they use similar foraging techniques. For instance, the Lemon-rumped Warbler (which breeds in conifer-mixed forests and winters in sal forests), mostly captures prey by hovering in the outer foliage of trees in both seasons.

Breeding Season

The Himalayas, because they provide such a huge variety of habitats, harbour one of the richest communities of leaf warbler species in the world. Twenty-one out of  the world’s 61 species of Phylloscopus are found in the Himalayan region. They occupy the entire range of habitats from tropical evergreen/deciduous forests in the foothills to the alpine meadows above the treeline. In the Himalayas the elevation zone 2500–3000 m supports the highest diversity of breeding warblers, where up to 9 species may breed together.

How do so many similar species coexist in one place? One reason is that while superficially leaf warblers are very similar, different species possess differently sized body parts. This is associated with differences in foraging behaviour. For instance, larger species eat larger insects and species with wider beaks catch more flying insects. Another way to allow coexistence is by occupying different elevation zones. To avoid competing for similar food using similar methods, each altitudinal zone in the mountain typically has one large species, a medium species and a small species, which capitalize on prey in accordance to their body sizes.
The overall drab colours of leaf warblers conceal subtle differences which not only indicate the habitat that they breed in, but also help in communicating and selecting mates. To the trained eye, visually distinguishing most of the leaf warblers involves relying on presence, number and colour of brighter patches such as wing bars, supercilium, rump patch and crown stripes. Species occurring in dense habitats, such as the Lemon-rumped Warbler, typically possess many bright patches (two wing bars, a distinct supercilium, crown stripe and rump patch). Such warblers often flash these patches to communicate. Additionally, males with brighter and longer wing bars are of higher quality (such males occupy larger territories) and are preferred by females. On the other hand, the Tickell’s Warbler, which breeds in open Juniper scrub, has no bright patches at all.

To be continued…Coming up next in this series: Tips for Identification of Phylloscopus Warblers

By Mousumi Ghosh

When I started birding seriously in the year 2005 after joining the Master’s course at the Wildlife Institute of India, I conveniently ignored every warbler I saw. Since visual identification was very difficult (given their frustratingly similar and drab appearances), I was happy enough to say that so-and-so bird was of a warblerish persuasion, and leave it at that. But then, as fate would have it, I wound up studying the wintering ecology of three species of leaf warblers in the Himalayan foothill forests of Himachal Pradesh for my MSc dissertation. While my primary motivation was to understand how they survive the winter sharing dwindling food resources, I now had to identify them accurately for my work to make any sense.

In most situations a bird in hand is worth two in the bush, but when it comes to identifying leaf warblers it is better to have a bird singing in the bushes than have even ten in your hand! This wisdom came to me from my supervisors Mr. Pratap Singh and Dr. Dhananjai Mohan, who taught me how to identify leaf warblers in the field from their calls and song.

These remarkable little birds belong to the family Phylloscopidae, whose members are dressed in various hues of dull green, yellow, grey and occasionally bright chestnut (as in the Chestnut-crowned Warbler). They are among the commonest species of European and Asian forests. The word Phylloscopus literally means ‘looking into the leaves’ and this aptly describes our industrious friends, who spend almost 75% of their waking hours searching for insects among the leaves. 

The genus is famed for its astounding diversity: more than 60 species of Phylloscopus are described. Most of them breed in the temperate areas of Europe and Asia. Despite weighing only 5-10g, some leaf warblers migrate over thousands of kilometres to arrive in their wintering quarters in the tropics of Africa and South Asia, including the Indian subcontinent. To cite an example, Hume’s Warbler (weighing just about 6 g) covers almost as much distance as the celebrated Siberian Crane (weighing 6 kg) to reach the plains of India from where it breeds in Siberia!

The same attributes which make them so difficult to identify (so many species, yet so similar in appearance) have made them one of the most well-studied groups of birds in the world. Within India, detailed studies of their breeding (in the Himalayas) and wintering ecology (Himalayan foothills, peninsular India) by Dr. Trevor Price and his students have revealed a great deal about these leaf warblers in both breeding and wintering seasons.

Read Part II of this series of articles on leaf warblers

By T. R. Shankar Raman

Originally published in ‘The Hindu’ on 1 November 2009

Every year, as the south-west monsoon fades across our land, a sense of restlessness and upheaval brews in the high Himalayas. The grey skies of August transform into the clear blues of September and a developing chill marks the air. The landscape and trees are gathering the colours of autumn; winter is not far. Then, in the high mountains, in ravines with willow and rhododendron, in lichen-encrusted forests of fir and birch, millions of little birds prepare themselves for a great journey.

The birds are so small that they can nestle snugly in the palm of your hand, or even fit into a loosely closed fist. They are most unassuming and drab, dressed in pale greens and humble olives, or in dull browns with scarcely a dash of yellow or orange, sometimes dabbed with pale wing-bars and stripes. They merge so well with the leaves that were they not so active and restless—flitting their wings and calling regularly to announce their presence—it would be hard to even spot them. And yet these wispy little birds, weighing around ten grams, can stake claim to great achievement. Every year, millions of them migrate hundreds to thousands of kilometres—in a matter of days even—flying south from the high Himalaya, the Caucasus and mountains of Central Asia to winter in the foothills, plains, plateaus, and hill ranges across India. And here, after a lull of many months, when the trees and shrubs are a-flutter with lively chirps and twittering song, we know that the leaf warblers are back.

Burning fat
The leaf warblers, as one may guess, have a close association with the foliage of shrubs and trees where they restlessly search for their insect prey. Their restlessness is heightened in the days that precede migration. The birds feed in the foliage, as if in a frenzy, to load up for their journey a crucial stock of fuel: a few grams of fat. That hundreds to thousands of kilometres can be efficiently travelled on a few grams of fat is one of the primal wonders of bird migration. Burning fat is more efficient than burning sugars or proteins, producing as a by-product water, another key need for those long hours on the wing.

Although many birds, including small ones like warblers, fly non-stop between their breeding and wintering grounds, the leaf warblers may make brief stop-overs en route. Thus warblers heading to the southern tip of India may be recorded on passage at sites in northern India or the Deccan in August-September and then again in April-May during the return journey.

Changing lifestyles
In southern India, the most ubiquitous of the leaf warblers is the Greenish Warbler. This species has three forms that differ slightly in plumage and call, which ornithologists sometimes separate into three species. It is found in a range of habitats from urban gardens and plantations to tropical forests, preferring the canopy of trees.

When these warblers leave the sub-tropical and temperate forests of the Himalaya or the mountains beyond for the tropical deciduous and evergreen forests of the south, it is not just the tree species and the habitat they use that changes. They make a fundamental change in their lifestyle. Up north, these warblers live and breed in pairs during the summer, each pair defending its territory from other pairs for its valuable trove of insect food.

Yet, when they come south for the winter, the males and females separate—each individual maintains its own territory. A female sings and defends a territory from other members of its species, just as a male does. Following the monsoon rains, insect prey are rich enough in the foliage to attract the warblers, but scarce enough to warrant staking out a territory to defend it from the warbler multitude.

The territories the birds defend are not large. A single hectare of tropical forest may pack two to four birds holding territories. By marking individuals with numbered and coloured rings on their feet, ornithologists have shown how the same individuals return to the very same quarter hectare of forest after their long journey every year—a feat of fidelity and orientation that one cannot help appreciating in so small a bird.

When the warblers arrive in our forests and gardens in September and October, they arrive singing. These are territorial songs staking claim to their all-important grove of trees or little segment of forest. During the first few weeks, the trees are busy with songs and territorial skirmishes as some warblers settle down in their winter turf and others are chased out of it. The songs then give way to simpler, short call notes serving to merely announce their presence (a boon to birdwatchers to detect and identify each species). Then, over a relatively quiet period, the warblers moult into a new set of feathers, as if to greet the new year.

Linking worlds apart
As April arrives carrying the promise of Himalayan spring, the relentless forces of nature and instinct turn the birds northward. Once more, the birds feed briskly to load up on fat. There is a flurry of song, as if in preparation for the territorial battles to be waged shortly on their breeding grounds. And then, one day, the tree where you have watched the warbler for several months is silent, and the bird is gone again.

And yet, when the warbler departs, it leaves behind a new awareness. An awareness, stirring deep wonder and strangely uplifting, that a tree in one’s garden may be linked to a specific, even if unknown, corner of the Himalaya by one individual bird. A renewed sensibility that the garden and that Himalayan corner, and a range of stop-over sites along the warbler’s route are all needed to keep alive this tiny linker of worlds. The warbler’s journey then seems a brave voyage of survival and connectedness, surmounting artificial boundaries and national differences in a way that transcends our best-intentioned bilateral efforts at cooperation. Softly and unobtrusively, as it has done for millenia, the little warbler continues to tie us to other lands and peoples and nations far away.

T. R. Shankar Raman is with the Nature Conservation Foundation.