Field Identification of South Indian Warblers

FIELD IDENTIFICATION OF SOUTH INDIAN WARBLERS
M.B.Krishna December 22, 2000.

Field Identification of South Indian Warblers Published originally in
the Newsletter for Birdwatchers, 29(3+4):4-11; April 1989; with
sketches by Dr. S. Subramanya. This is a much enlarged update of
Krishna, M.B. 1986. Clues for identifying Warblers. Newsletter for
Birdwatchers 26(5-6): 20-21.

Field identification of warblers presents some initial difficulties
due to an inadequacy of prominent differences between species and
genera in colour, colour patterns or in other features. As a group,
they are very active birds which are shy of human presence. This
necessitates patient, methodical observation and, making field notes
and sketches which many birdwatchers tend not to do. Moreover, what is wanting in our bird books is a more detailed description, with more emphasis being given to structural features. In the absence of a
detailed description, it becomes necessary to go through species
accounts more carefully to extract maximum information possible. One might, for example, need to go through even the section entitled
"Museum Diagnosis" in the Ali-Ripley Handbook. It may also become
necessary to look into measurements of the structures to get an idea
of the proportions, though one need not attach much importance to
finer differences for field identification. What is important here,
are the gross differences as can be made out in the field using
binoculars or Telescopes.

This article is a compilation of such information covering South
Indian Warblers only, from relevant sources supplemented by personal observations wherever possible. Its validity, usefulness and
relevance has to be evaluated by the reader who wishes to make use of it. As such, this is only a beginning. A basic familiarity with the
group is assumed.

This article consists of three sections. The first deals with defining
the terms used in the rest of the article and elucidating the
variations in characteristics found in the subfamily. The second is an
attempt to rationalise and systematise the approach for the
identification of the major groups. The third is an overview to help
recognise the genera.

TERMS USED AND VARIATION IN THE SUBFAMILY

The range of variation seen in the various body parts within the
Subfamily Sylviinae is brought out in this section.

BEAK LENGTH

Beak length is taken relative to the size of the head. An imaginary
line drawn along the length of the beak extending to the back of the
head provides the reference line. If the distance from the beak tip to
its base is equal to the distance from the beak base to the back of
the head (in profile), then the beak is said to be equal to the head.
This is the case in genera Orthotomus and Acrocephalus. In Cisticola,
Prinia and Hippolais, the beak is just two-thirds the length of the
head. In other genera, it is only half.

HEAD PEAK

The shape of the head can vary. It could be rounded or angular. The
top-most point of the head may fall over or behind the eye giving
characteristic shapes to the head, especially the crown. For example,
in Acrocephalus the peak falls behind the eye while in Hippolais it is
just over the eye.

WING LENGTH AND SHAPE

If the primaries extend much beyond the secondaries in a closed wing,
then it is called a long wing. If not, it is short. The differences in
the lengths of the various primaries determines the shape of the wing;
that is, whether it is rounded or pointed. In many genera, a 'wing
formula' is used to distinguish the species in the hand. This
expresses the ratio in the length of some of the primary feathers.

TAIL

The tail shows a lot of variation in the subfamily. The differences
lie in the shape, length and the way it is held. If the length of the
tail is more than the length of the wing, then it is said to be a long
tail. It could be held in line with the body, or held cocked; it could
be long or short, graduated, rounded, fan-shaped, square or notched.
The undertail coverts can also show a lot of variation. It could be
very long, extending to more than two-thirds of the tail as in
Locustella, or short, blunt and within half to a third of the tail as
in Hippolais, or be intermediate, as in Acrocephalus.

TAIL, TAIL-TIP: SPECIES
Long tailed, graduated: Prinia, Orthotomus, Chaetornis, Schoenicola,
Phragmaticola
Long tailed, fan-shaped: Cisticola
Long tailed, rounded: Locustella, Acrocephalus
Short tailed, square: Hippolais
Short tailed, notched: Phylloscopus
Short tailed, slightly rounded: Sylvia

BODY SIZE

For field identification, apart from finer comparative size
estimates, it is essential to distinguish whether a warbler is
smaller, equal to, or larger than a sparrow. The small warblers are
Cisticola, Prinia, Orthotomus, Locustella, Hippolais, Phylloscopus,
Sylvia curruca, Acrocephalus agricola and Acrocephalus dumetorum.
Large warblers are Chaetornis, Schoenicola, Phragmaticola and
Acrocephalus stentoreus.

BODY SHAPE

A sketch of the overall body shape would be useful, though not
essential, during field identification (except perhaps in some
specific cases). The body profile, plumpness, whether deep chested or
not, whether the bird seems to carry more bulk forward or aft when
perched, etc, would all be helpful points to note. Along with this,
the posture taken, that is, whether the bird tends to perch upright or
horizontally should also be noted.

HABITAT

There are essentially two groups, those that prefer predominantly
grassy areas and those that do not. Cisticola, Prinia, Locustella,
Schoenicola, Phragmaticola, and Acrocephalus essentially (though there
may be a few exceptions) prefer areas with vertical grassy or reedy
vegetation. Orthotomus, Hippolais, Sylvia and Phylloscopus prefer
arborescent or dicot vegetation.

ACTIVITY AND GENERAL BEHAVIOUR

Almost all warblers are shy birds which sulk when disturbed. There are
a few behavioural traits or"mannerisms" which are of some importance
in field identification. Such behaviours include flushing, flicking
wings and tail, clambering up stems or hopping amongst twigs, making
short sallies, etc. Many call constantly when foraging. Grassland
warblers tend to clamber up reeds or stems and call from exposed
perches in the evenings and mornings. Hippolais, Sylvia and
Phylloscopus tend to leave their perches frequently to make short
sallies after flying insects, flushed by their incessant movements
like flicking open wings and tail. Such behaviour is very
characteristic and helps in placing the bird immediately into its
group (as in Phylloscopus).

CALLS

Calls of warblers vary. Many of the genus Prinia, Orthotomus,
Chaetornis, and Phylloscopus have pleasant, usually multi-syllabled
calls given out while foraging or from exposed perches. The first two
have similar alarm calls. All the genera of migratory warblers except
Phylloscopus (ie. Locustella, Phragmaticola, Acrocephalus, Hippolais,
and Sylvia) have a tek, tschek, chek, chuk or churr call given out
frequently and in many such cases the alarm call is a harsh churr. The
alarm is not always given when disturbed. The bird may flush, only to
disappear into the vegetation once again.

COLOUR PATTERNS AND PLUMAGE

Most of the warblers are sober coloured birds with almost no bright
colours on them. Warblers of grassland and dry regions are
predominantly brown, while greens predominate in woodland warblers
(like many Phylloscopi). Almost all have a dorsal-ventral colour
difference and are paler below. The most important aspect of plumage
colour in warblers is the pattern. The presence or absence of stripes,
streaks, and bars provide important clues for identification.

WING BARS

These are paler coloured edgings to secondary covert feathers. They
appear as short bars across the length of the closed wing. Presence or
absence, colour and number are important points to be noted in the
genus Phylloscopus.

CORONAL STRIPES AND BANDS

Broad or narrow longitudinal patterning on the crown of many
Phylloscopi are helpful in distinguishing species, for example, P.
occipitalis from P. trochiloides.

STREAKS AND STRIPES

Either the upperparts or underparts may be streaked in many warblers.
Chaetornis has bold dark streaks on the upperparts which makes it
distinctive amongst the South Indian forms. Cisticola and Locustella
also have streaked species.

SUPERCILIA

This is the 'eyebrow' of the bird and is quite often pale whitish.
Colour and length of the supercilia are important diagnostic
characters in Phylloscopus and Acrocephalus.

A SCHEME FOR IDENTIFICATION

There are many ways to approach the problem of field identification of
warblers. An attempt has been made here to provide some guidelines for
the identification of major groups in the form of a key. It should be
noted here that this is not intended to be infallible, but is meant
only for a systematic beginning.

KEY

1 Small sized warblers, equal to or smaller than a sparrow ...5
- Large sized warblers: larger than a sparrow and about the size of a
bulbul ...2

2 Bill long: as long as the head Acrocephalus stentoreus
- Bill short: about half the length of the head ...3

3 Upperparts boldly marked with dark dot like streaks Chaetornis
striatus
- Upperparts not marked with spots streaks, etc. ...4

4 Huge: bulbul sized; about 20cm long; no supercilium Phragmaticola
aedon
- Smaller: about 17cm long; between sparrow and bulbul in size; short
indistinct supercilium; tail broad Schoenicola platyura

5 Bill as long as head ...6
- Bill 2/3 of head ...7
- Bill 1/2 of head ...8

6 Upperparts brown; colour of head same as that of upperparts
Acrocephalus
- Upperparts green; colour of head rusty and not same as rest of
upperparts Orthotomus

7 Wings long; tail shorter than wing; undertail coverts short, less
than half to a third of the tail Hippolais
- Wings short; tail fan shaped and rounded, equal to or shorter than
wing; undertail coverts normal Cisticola
- Wings short; tail longer than wing, graduated and often held cocked;
undertail coverts normal Prinia

8 Tail rounded, undertail coverts very long; head/upperparts streaked
Locustella
- Tail square, not long; undertail coverts normal; throat white,
contrasting with dark cheeks or dark head cap Sylvia
- Tail square or notched, not long; undertail coverts normal;
upperparts greenish or brownish, with or without wing bars and coronal
stripes; supercilium present; very active warblers Phylloscopus

RECOGNISING THE GENERA

In this section, the objective is to help place the warbler seen into
its correct genus.

GENUS CISTICOLA: FANTAIL WARBLERS

Very small warblers. Bill 2/3 head. Tail evenly rounded and fan-like.
Wings rounded. Two species, both residents. Found in tall grass,
predominantly wet (Paddy) cultivation, low scrub, and similar
habitats. The short rounded tail is frequently jerked open like a fan.
Unobtrusive in tall grass. Singly or in loose parties. Flush when
approached and disturbed. Individuals mount to the top of grass blade
or stem to sing or have a display flight. From cista = chest or box
(L); kistos = rock rose (G); colo = to inhabit (G).

GENUS PRINIA: LONGTAILED (OR WREN-) WARBLERS

Size small. Bill 2/3 head. Tail long and graduated. Wings rounded and
feeble. Four resident species preferring grassland, scrub with grass,
cereal and millet cultivation, and gardens. Hop, flit, clamber and
creep about among grass and bushes in a characteristic erratic and
jerky manner, tail erect and loosely flicked up, down and sideways.

GENUS ORTHOTOMUS: TAILOR BIRD

Small size. Bill equal to head in length. Tail long and graduated.
Wings very short and rounded. One resident species with rusty head and
olive green upperparts. Common and widespread from scrub country to
woodland and gardens. Usually keeps down low in herbage and
undergrowth, hopping about energetically, tail erect and constantly
flicked from side to side, uttering its loud familiar call. Not averse
to hop on to the ground or go into a tree, even on to the crown of a
Coconut Palm!

GENUS LOCUSTELLA: GRASSHOPPER WARBLERS

Small size. Bill about half the length of the head. Tail very much
graduated. Undertail coverts very long. Crown or upperparts streaked.
Two migratory species found in swamps, reedbeds and Paddy fields.
Great sulkers, usually flushed when almost trodden on, diving headlong
into cover after a short jerky flight low over the herbage and
threading the way swiftly through the root stocks. Almost impossible
to flush a second time. From locusta = spikelet of grass (L);
Locustelle = Grasshopper Warbler (Fr).

GENUS SCHOENICOLA: BROADTAILED GRASS WARBLER

Size large. Bill half of head. Wings long and well developed. Tail
long, broad and graduated; looks large. Undertail darker. One resident
species found in marshy depressions with high grass and reeds. Perches
vertically and keeps tail down. Whenever the bird clambers up a reed
stem and perches upright, it appears as though the bird is weighed
down by its tail. Habits very similar to Chaetornis but an inverterate
sulker like Locustella, flushing with difficulty only when almost
trodden on and diving into cover to disappear from view. Flight
indirect and 'tail heavy' like that of a Prinia, the broad graduated
tail conspicuous on the wing. From schoinos = rush or sedge; colo = to
inhabit (G).

GENUS CHAETORNIS: BRISTLED GRASS WARBLER

A large warbler with a stout bill half the length of the head and tail
equal to wing. Strong rictal bristles arranged in a vertical row in
front of eye. Feathers of breast sometimes dark shafted, but stiff,
forming a 'necklace'. The only warbler with bold dark brown streaks on
back. One resident endemic species preferring coarse grassland and
cultivation with bushes. Keeps singly or in pairs sulking or moving
swiftly through grass, occasionally exposing itself at the top,
tumbling headlong into cover on disturbance and difficult to flush
again. Calls pleasant. Rather similar to a Common Babbler on a
fleeting glimpse. From chaite = mane or flowing hair; ornis = bird
(G).

GENUS PHRAGMATICOLA: THICKBILLED WARBLER

The only species in the genus, P. aedon is now shifted to the genus
Acrocephalus (Ripley, 1982). Bulbul sized. Bill wide and short; half
the length of the head. Tail very much graduated with narrow feathers.
Wings pointed. One migratory species preferring marshy places,
secondary growth in forest clearings, tea and coffee plantations.
Solitary, rather secretive and usually seen when flying from one bush
to another. Hops about in the undergrowth and reeds close to the
ground, occasionally making short sallies after flying insects. Looks
like the Great Reed Warbler, but with shorter beak and no supercilium.
From phragma = hedge or fence; colo = to inhabit (G).

GENUS ACROCEPHALUS: REED WARBLERS

Sizes varied. Bill slender and equal to head. Crown peak behind eye.
Tail rounded. Three species, the smaller two being migratory. Found in
reed beds and bushes in damp places. One species found commonly in
gardens and far from water. Keeps singly within thick cover, calling
frequently and hopping from stem to stem, clinging sideways and often
lunging to snap up tiny insects. From acros = pointed; cephalus = head
(G).

GENUS HIPPOLAIS: TREE WARBLER

Size small. Bill about 2/3 head. Tail square or rounded at edges.
Undertail coverts short. The body often appears plump and has a rather
flat back and tail line, extended by a prominent head. When perched,
they often appear to carry more bulk forward of the legs than aft,
looking sometimes short tailed in the field. Both completely upright
and horizontal postures are adopted by moving and perched birds. There
is often a hint of clumsiness or carelessness in their acrobatic
progress through cover. Closely resembles the leaf warblers in
behaviour and movements, often flying out from the extremity of a twig
to take insects on the wing, but usually keeps to well within the
canopy. One migratory species found in Acacia scrub and deciduous
country.

GENUS SYLVIA: WHITETHROAT AND ORPHEAN WARBLER

Small to medium sized warblers. Bill half the length of head. Tail
square or slightly rounded. Two migratory species found in scrub and
semi-desert. Both species have characteristic plumages with pure white
throat contrasting with dark cheeks (as in Whitethroat) or dark head
cap (as in Orphean Warbler). In habits, they are quiet, unobtrusive,
sulking, usually solitary and restless. Along with tree warblers,
Whitethroats have a habit of lunging out to seize an insect just out
of reach, nearly toppling over in the attempt, then quickly steadying
themselves on the wings. From silva = forest (L).

GENUS PHYLLOSCOPUS: WILLOW OR LEAF WARBLERS

Very small and very active warblers. Tail square or notched, not long.
Four to eight migratory species found from deciduous woodland to
evergreen forest. In this group, difficulties arise in observing the
birds not because they are shy, which they are not, but because they
are so active. They flick wings and tail almost continuously and make
short sallies after fleeting insects, resuming searching amidst the
foliage immediately after. The calls are pleasant. From phyllos =
leaf; skopos = watcher (G).

SOME REMARKS

There are shortcuts to identifying warblers, though being careful and
methodical can never be over emphasised while observing them.
Eliminating groups one is familiar with, right in the beginning, does
help and leaves one with a more manageable set of alternatives.
Counter-checking the field identification with a complete reference
description should serve to verify the result.

ACKNOWLEDGEMENTS

I gratefully acknowledge the help, advice and encouragement given by
Dr. Joseph George and also thank Dr. S. Subramanya for volunteering to
do the sketches and commenting on the draft.

SELECT BIBLIOGRAPHY

1 Alexander, H.G. 1969. Some notes on Asian Leaf Warblers (Genus
Phylloscopus). Published by the author.
2 Ali, Salim. 1969. Birds of Kerala. Oxford University Press.
3 Ali, Salim & Ripley, S.D. 1973. Handbook of the Birds of India and
Pakistan. Volume 8. Oxford University Press.
4 Baker, H.R. & Inglis, C.M. 1930. The Birds of Southern India.
Superintendent, Madras Government Press.
5 Krishna, M.B. 1986. Clues for identifying Warblers. Newsletter for
Birdwatchers 26(5-6): 20-21.
6 Ripley, S.D. 1982. Synopsis of the Birds of India and Pakistan, 2nd
edition. Bombay Natural History Society.
7 Sharrock, J.T.R. (ed). 1980. Frontiers of Bird Identification, a
'British Birds' guide to difficult species. Macmillan.
8 Wallace, D.I.M. 1964. Field Identification of Hippolais Warblers.
British Birds 57: 282-301. Reprinted with postscript in Sharrock,
1980.

COPYRIGHT (C) M.B.KRISHNA, 1989, 2000

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