How’s that long-term effort to review all the passerine bird groups of the world going, huh? Well, it’s not going well at all. So….
I tend to fixate for a little while on animals I get to see in person. At the time of writing I’ve just returned from a day trip to Itchen Valley Country Park (Southampton, southern England) where I watched co-operative warblers (of several species) at reasonably close range. For that reason I have warblers on my mind.
Caption: I haven’t drawn representatives of all the passerine groups yet, but I’m working on it (these drawings are for my STILL in-prep giant textbook project). All of these groups - and others - were long lumped together in a super-inclusive version of Sylviidae, a catchall ‘warbler’ family. We now know that they’re separated by various other ‘family-level’ lineages. Image: Darren Naish.
An interesting point worth making right at the start here is that the various slim-billed, insectivorous, skulking, highly active, mostly cryptically coloured passerines traditionally grouped together as warblers (and lumped together in ‘Sylviidae’) are not – as was long thought – close allies, but distantly related on the family tree. All are members of Sylvioidea, but various ‘non-warbler’ lineages (like long-tailed tits and bushtits, white-eyes, babblers, laughing-thrushes and so on) separate them from one another. It’s probably best to imagine the term ‘warbler’ as applying to an ecomorph that has evolved repeatedly within the sylvioid clade… lumping these birds together in a super-inclusive version of Sylviidae always was lazy, since the groups concerned are highly distinct and only vaguely similar once you start looking at them. Sylviidae, incidentally, is today restricted to Sylvia (cough and Curruca cough).
Here, I want to look specifically at the Locustella warblers, a warbler group (containing around 25 species) of Eurasia, Africa and Australasia that might best be termed the grass warblers or grasshopper warblers.
They’re part of Locustellidae (Megaluridae is currently considered synonymous). Bush warblers*, grassbirds, fernbirds, songlarks and thicketbirds also belong to Locustellidae. While a minority of locustellids are moderately spectacular in appearance (Malia, I’m looking at you**), they’re predominantly brownish, with streak-like dorsal marks, rounded wings and a longish tail. It might just be me, but I always imagine them as having a sort of archaic, ‘ancestral’ appearance relative to other sylvioids.
* Not to be confused with the birds called bush warblers included within another sylvioid group: Cettiidae.
** Malia grata – its only common name is the Malia – is a relatively big, greenish-yellowish Indonesian endemic, conventionally regarded as a bulbul. Its unusual appearance explains why it wasn’t regarded as a locustellid until molecular phylogenetics rode into town (Oliveros et al. 2012).
As is typical for bird groups, molecular studies have found that the conventionally recognised genera in Locustellidae are not monophyletic (Alström et al. 2018; see also Drovetski et al. 2004), a taxonomic consequence of which is that Locustella of tradition has been ‘reduced’; some, mostly east Asian species formerly included in the genus are now recognised as Helopsaltes. This makes sense (I think), the species concerned (like Gray’s grasshopper warbler H. fasciolata, the Sakhalin grasshopper warbler H. amnicola and Pleske’s grasshopper warbler H. pleskei) being mostly very distinct from the ‘core’ Locustella species. They’re chunkier, proportionally thicker-billed, and superficially more ‘thrushy’ than Locustella warblers.
The Locustella species proper are, of course, named for their songs (‘Locustella’ = little grasshopper), which are most certainly not complex, passerine-like outbursts as we usually imagine them but instead continuous, monotonous buzzes or trills which totally sound like the calls of crickets. A singing Locustella warbler opens its mouth wide and emits this sound (usually while perched or clinging close to the top of a reed in a reedbed) continuously for tens of seconds at a time, all the while looking about as if aiming to spread the sound around itself as much as possible. You really have to wonder what’s going on with its syrinx all the while, since there sure must be some interesting things happening.
Caption: a singing Lanceolated Warbler Locustella lanceolata, a species which occurs from Scandinavia in the west to the shores of the Pacific in the east, and which migrates to south-east Asia during the winter. Image: Денис Жбир, CC BY-SA 4.0 (original here).
Migrating and not migrating at all. Eurasian Locustella warblers are (mostly) migratory, only coming to Europe and/or northern Asia in the warmer part of the year: they arrive in April or May and leave in August or September. European and west Asian species spend the rest of the year in Africa. We usually think of them as ‘sub-Saharan’ migrants but that’s not strictly true as individuals in some species (like the Grasshopper warbler L. naevia) winter in Mauritania, Morocco, Algeria and elsewhere in the north. Eastern species – examples include the Chinese bush warbler L. tacsanowskia and Baikal bush warbler L. davidi – winter in India, southern China and southeast Asia. Even Sumatra, Borneo and the Philippines are visited by species like the Lanceolated warbler L. lanceolata.
The actual physical act of migration isn’t especially well understood but the fact that migrants are rarely reported and those that are reported tend to have massive fat stores suggest epic, unbroken flight events that (among species of the west) involve leaving northern Europe, a single stopover in northern Africa, and then a continuing south again. Locustella warblers are a common prey item of Eleonora’s falcon Falco eleonorae in northern Africa (Cramp 1992), itself a migratory species too.
Caption: the sort of place in northern Europe where you might find Locustella (and warblers of other groups too) during the warmer part of the year. This is a mix of damp grassland and river-edge reedbed with scattered small trees and large shrubs. Image: Darren Naish.
The summer breeding grounds of these birds involve lowlands and valleys where moist meadows, riverbank foliage and scattered trees occur, but steppes and even cereal fields are used too, so long as there are sufficient stands of shrubs, trees and tall grasses. Cover is essential for these birds: they’re notoriously cryptic and reluctant to appear in the open. When among foliage, they scurry and clamber about in horizontal poses (the term “mouse-like” is often used for their style of movement; Cramp 1992), only rarely appearing at perches or in the open, and they’ll even hide in boulder piles. Their wintering grounds include grass-dominated forest clearings in African countries like Sierra Leone and Guinea and paddyfields and reedbeds in east Asia.
However, it isn’t that all Locustella species are migratory: there’s a respectable list of sedentary island endemics too, including on Sulawesi, the Moluccas, the Philippines, Borneo, Taiwan, Java and Timor. And there are also resident species in continental Asia too, like the Annam grasshopper warbler L. idonea in Vietnam and Sichuan grasshopper warbler L. chengi in China. Nothing’s ever simple. Indeed, some studies have shown that these highly mobile birds can evolve relatively sedentary morphs relatively quickly, should conditions allow (Neto et al. 2012).
Caption: non-migratory habits have evolved on numerous occasions within Locustella. Here are two non-migratory island endemics: Friendly bush warbler L. accentor of Borneo at left, and Sulawesi bush warbler L. castanea of Sulawesi at right. Images: John Keulemans (in public domain); A. S. Kono, CC BY-SA 3.0 (original here).
Some behaviour. Insects and arachnids of many sorts are taken as prey by Locustella, as are small gastropods and occasional seeds. A wide variety of unusual display postures and actions have been reported for populations of the widespread Grasshopper warbler L. naevia (and other species too). These include wing-waving, a singing pose where the bird stands erect, bill pointed skywards, and singing with the wings elevated.
Males will also select and carry leaves during mating displays and pass them to females, all the while standing in a lowered pose with the wings outstretched: you probably know that the ‘presenting’ of symbolic nesting material happens in such birds as grebes, but its existence in passerines isn’t especially well known. Finally, Locustella warblers are not especially long-lived, the oldest ringed individuals being around 4 years old.
And here’s where things come to an end. I hope you enjoyed this brief look at this interesting group: a mainstay of fieldguides which you’ll surely be familiar with if you watch birds in Europe, Asia or Africa, but a group which is little discussed and generally glossed over.
Caption: now you may no longer dread those few specific pages of your favourite field guide :) And… yes, those are Locustella warblers on the cover of BWP Volume VI (art by Ian Lewington). Image: Darren Naish.
For previous TetZoo articles on passerine birds, see…
Great tits: still murderous, rapacious, flesh-rending predators!, February 2013
For The Love of Crows, October 2015
Thoughts on the Passerine Tree, 2016, October 2016
A Battle Among Blue Tits, February 2018
Cocks-of-the-Rock, Extreme Cotingas, April 2019
Birdwatching in Suburban China, May 2019
Tell Me Something Interesting About Dunnocks, July 2019
Suburban Birdwatching in Queensland, Australia, November 2019
Kirk W. Johnson’s 2018 The Feather Thief, a Review, February 2021
Ref - -
Alström, P., Cibois, A., Irestedt, M., Zuccon, D., Gelang, M., Fjeldså, J., Andersen, M. J., Moyle, R. G., Pasquet, E. & Olsson, U. 2018. Comprehensive molecular phylogeny of the grassbirds and allies (Locustellidae) reveals extensive non-monophyly of traditional genera, and a proposal for a new classification. Molecular Phylogenetics and Evolution 127, 367-375.
Cramp, S. (ed). 1992. The Birds of the Western Palearctic. Volume VI. Warblers. Oxford University Press, Oxford.
Drovetski, S. V., Zink, R. M., Fadeev, I. V., Nesterov, E. V., Koblik, E. A., Red’kin, Y. A. & Rohwer, S. 2004. Mitochondrial phylogeny of Locustella and related genera. Journal of Avian Biology 35, 105-110.
Oliveros, C. H., Reddy, S. & Moyle, R. G. 2012. The phylogenetic position of some Philippine “babblers” spans the muscicapoid and sylvioid bird radiations. Molecular Phylogenetics and Evolution 65, 799-804.
