Re-Booting the identification of Hippolais warblers

This entry was posted Friday, 9 March, 2012 at 1:22 pm

By R. Jayapal

Dr R. Jayapal is an assistant professor at the School of Human Ecology, Ambedkar University, Delhi. Essentially a birdwatcher trained in wildlife ecology and conservation, he has been doing ecological research on birds for more than 15 years, and has worked in various landscapes across India ranging from the Central Indian Highlands of Madhya Pradesh to the trans-Himalayas of Ladakh.

Until the 1990s, life used to be simple and straightforward for a serious warbler-watcher in the Subcontinent. One would know this was a Chiffchaff and that was a Booted Warbler. Although both had two subspecies wintering in our region, one normally wouldn’t bother about that as all the literature would say it was nearly impossible to identify them unless in hand. I also suspect that just identifying them authoritatively as a Chiffchaff or a Booted Warbler in the field was esoteric enough to impress and awe others. But things changed with the increased use of DNA to lump or separate species, supported by analysis of vocalizations in the field. These developments have both advanced the science of taxonomy and jolted us good old birdwatchers and subverted our long-cherished complacency.

The Chiffchaff has been split into Common Chiffchaff and Mountain Chiffchaff (actually more, but that’s another story) and the erstwhile Booted Warbler has been found to consist of two species – Sykes’s Warbler (Hippolais rama) and Booted Warbler (Hippolais caligata). [They were initially treated so in 19th century, but then that was before the era of trinomial nomenclature].

Now to the mundane, but yet the most pertinent question –– is it possible to differentiate these two Hippolais warblers in the field? The answer is Yes and No… Yes, if you are careful to note down some subtle yet distinct field-characters and fortunate to observe the birds in fresh plumage closely. No, if you are a birder like me who does not have those discerning pair of eyes and who has this inexplicable habit of always encountering birds in worn plumage or moult, or worse, individuals showing intermediate characters (Apparently, they do hybridize).

To begin with, a birder is more likely to come across two types of Hippolais warblers: one that looks like a reed-warbler (Acrocephalus) but behaves typically like a leaf-warbler (Phylloscopus), and another the other way round. If this peculiarity strikes you in the field, well, half the battle is won. [Warning: Judging a bird as a look-alike or behave-alike can become subjective].

Sykes’s Warbler (H. rama), with a longer bill and a longer, graduated (i.e., narrowing in steps) tail, looks strikingly (!) like an Acrocephalus reed-warbler. It also has a relatively longish body (from bill to tail tip) that is accentuated by somewhat longer under tail-coverts. But, despite its reed-warbler-like appearance, its foraging behaviour is strangely reminiscent of a Phylloscopus leaf-warbler. You can see it actively gleaning and flycatching in the middle- and top canopy of tall shrubs and low trees, rarely descending down to ground-level vegetation. Both the Hippolais often twitch and flick open their tails, and while doing so, rama’s graduated tail feathers are hard to miss.

Other diagnostic characters of rama may be either difficult to observe in the field or may not always be conspicuously present in all the individuals. These include: a completely pale yellow lower bill lacking any dark-tip, absence of darker margin to the short white supercilium (just above the lores), and pinkish-brown legs (which are slightly darker compared to caligata’s pale yellow tarsus).

Booted Warbler (H. caligata) has a comparatively shorter bill and a squarish, shorter-looking tail with an abruptly-ending belly (owing to much shorter under tail-coverts). These features make the bird look rather like a Phylloscopus leaf-warbler. H. caligata distinctly lacks the proportionately long body plan of rama. When the tail is twitched open, the Phylloscopus-like squarer tail feathers are quite unmistakable (contra rama). The Booted Warbler invariably forages like an Acrocephalus reed-warbler among the undergrowth and herbage at the ground-level (though more tame than many Acrocephalus). It does, however, occasionally visit the middle canopy only to return to lower vegetation in a moment or so.

As described under rama, there are other diagnostic characters of caligata that may not always be useful in the field. These include a dark-tipped pale lower-bill, a dark supra-ocular margin just above the lores (present only in fresh plumage), and paler looking legs.

It is important to note that both rama and caligata have almost indistinguishable calls in their winter quarters – a hard and dry chuk. And it should be remembered here that NOT ALL individuals are identifiable with certainty in the field, as individuals with intermediate characters are ‘not uncommon’ (ah, what a wonderful phrase!). There have also been recent revisions in the taxonomy of Family Acrocephalidae resulting in placement of both these Hippolais taxa in the genus Iduna along with Thick-billed Warbler.

One should also keep in mind that the wintering ranges of both rama and caligata have not been completely worked out as all our current understanding is based on museum collections and subspecies identity was not possible in a majority of past sight records (For more information, see P.C. Rasmussen & J.C. Anderton, 2005. Birds of South Asia: The Ripley Guide. Smithsonian Institution, Washington DC & Lynx Edicions, Barcelona). For all practical purposes, both taxa are likely to occur in most parts of the Subcontinent (probably except the higher Himalayas and north-eastern hills) either as winter visitors or passage migrants.

If you do find these tips helpful (or hopeless) in the field, please do write to me as that would greatly reassure me (that I am not alone).

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You can contact R Jayapal at rajah.jp[at]gmail[dot]com

3 Comments to Re-Booting the identification of Hippolais warblers

  1. Manoj Nair says:

    March 12th, 2012 at 1:53 pm

    Jayapal,

    Rama, rama !

    The tips will indeed be of help in field; thanks for demystifying the Hippolias.

    Do keep writing…

    Manoj.

  2. Krishna MB says:

    May 21st, 2012 at 9:00 pm

    sketches could have been used to illustrate the differences which have been described in words.

  3. Kannan AS says:

    February 14th, 2016 at 1:15 pm

    Thanks for this wonderful piece, very helpful!

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