CBCN May 2013 page 106 to 116

Based on the Analysis and Evaluation of the Ceylon Bird Club Notes (CBCN) 1956-2005  by Guenter Lamsfuss

Author's Note:  This paper was submitted to the CBCN in 2007, but the then Editor, Udaya Sirivardana, suggested to me that it be delayed until further investigations were carried out on certain distinct colour forms in the northern population of the species then considered hybrids. Now he, and Deepal Warakagoda who has done so, have requested that it be re-sent in more-or-less the original form.

In modern taxonomy, the Ceylon Golden-backed and the Red-backed Woodpeckers are treated as two endemic subspecies of the Black-rumped Flameback or Lesser Golden-backed Woodpecker of India, Dinopium benghalense, while in the past, the classification as well as the naming of the two forms was different. A recent evaluation of the CBCN covering the
50 years period of 1956-2005 suggests that further observation and study may lead to a revision of the current status.

History

Layard (1853) in his "Ornithology of Ceylon" uses Brachypternus aurantius and Yellow-backed Woodpecker as the names of the golden-backed form and writes that this species is "confined exclusively to the Borassus-growing districts, commencing at Chilaw sparingly, and increasing in numbers till its knocking resounds from almost every palmirah tope in the Jaffna peninsula". He calls the red-backed form Brachypternus ceylonus and states that it is peculiar to Ceylon, replacing B. aurantius in the South and central parts of the island, being very common in the low country.

Legge (1880) in his "History of the Birds of Ceylon" employs the names Brachypternus puncticollis, the Southern Golden-backed Woodpecker which inhabits - in various shades of back colour - India and northern Ceylon. He characterises it as one of the most difficult birds to deal with in the whole of his work. He writes that in Ceylon, the pale (golden-backed) form inhabits the Jaffna Peninsula and the adjacent coasts down to Puttalam and Trincomalee, while birds with reddish-orange coloured backs are found in the shady forests throughout the northern half of the island. Taxonomically, he treats the Ceylon population as part of the South Indian, but for a short time in between refers to the reddish variants of northern Ceylon as of the race "intermedius". He also mentions that further investigation may lead to a revision of the classification and adds that very dark reddish birds may possibly be hybrids between the Golden-backed and the Red-backed Woodpecker.

Like Layard, he treats the Red-backed Woodpecker as a full endemic species Brachypternus ceylonus and writes that this species “… is diffused throughout the entire island, with perhaps the exception of the extreme north of the Vanni and the Jaffna peninsula. It is abundant in the Western and Southern Provinces … and equally so in the interior of the Eastern Province, and scarcely less so in the jungles between Matale and Trincomale and in the N.W. Province. Mr. Holdsworth did not observe it in the Aripu district, nor did I meet with it there nor in the island of Mannar; some distance inland from Mantotte it is, I am informed, not uncommon, as also further north in the Vavoniya Valankulam district”.

Wait (1920) in his notes on "Picarian birds ... of Ceylon" also treats the Red-backed Woodpecker as a separate, endemic species and refers to the reddish-coloured birds as the "forest race" of the Golden-backed Woodpecker. He describes the coloration of these birds as "yellow tinged more or less with orange, or even red; some specimens are so red that they are probably hybrids between the two species". Later, in his "Manual of the Birds of Ceylon" (1931), he follows Baker (1927) in both the classification and the naming of the two forms, but does not assign the intermediate birds to either. In regard to distribution, he writes that the Golden-backed Woodpecker occurs in the extreme North of Ceylon, and is replaced in the South by the Red-backed. He adds  "Over the greater part of the northern forest tract birds are frequently intermediate between the two forms, the hue of the back varying from pale orange yellow to orange red".

Baker (1927) in his F.B.I. treats the two Ceylon Woodpeckers as endemic races of the Indian Golden-backed Woodpecker Brachypternus benghalensis, but gives the Ceylon golden-backed form the status of an endemic subspecies ceylonus and names the red-backed form erithronotus. As far as intermediate birds are concerned, he assigns them to the golden-backed race ceylonus and writes that in the central, wetter and better forested areas of the North, birds show a considerable amount of red in the upper plumage.

Whistler (1944) in his "Avifaunal Survey of Ceylon" attempts to straighten out the earlier disorder. Based on the specimens he collected, he concludes that - in accordance with Baker - the Golden- and Red-backed Woodpeckers are two endemic races of the same species, but names the golden-backed subspecies jaffnensis while keeping erithronotus for the red-backed race.

Of jaffnensis, he writes that this race "inhabits the Jaffna Peninsula and the adjacent coast down to Mannar; further south it apparently extends, but less plentifully to Puttalam on the west and to Trincomalee on the east coast. In its pure, golden-backed form it is a bird of the open coastal areas, avoiding the inland forests". He further writes that in the northern forest tracts, there is intergrading between the two forms, with golden-backed and intermediate birds occurring as a haphazard minority, and red-backed birds predominate. Taxonomically, he assigns the intermediate birds to the red-backed race erithronotus and writes that the latter occupies the whole of the island up to but excluding the northern coastal areas, defined as the habitat of jaffnensis.

Phillips (1953) in his "Nests and Eggs of Ceylon Birds" writes that the Ceylon Golden-backed Woodpecker Dinopium benghalense jaffnense is the northern representative of the common Red-backed Woodpecker D. b. erithronothon. "It is plentiful in the coconut and palmyra groves of the Jaffna Pensinula and southwards throughout the jungles and well-wooded areas of the Northern Province to near Anuradhapura in the North Central Province, where it meets and intermingles with the red-backed form". Further, he writes that "... intermediates between the two forms are not uncommon as far as Kekirawa and sometimes even further south. Likewise, on the West Coast, the golden-backed form is fairly plentiful as far south as Mannar and on the East, to Trincomalee".

Henry (1971) in his "Guide to the Birds of Ceylon" adopts the current taxonomy and writes that the two forms freely interbreed in the inland areas of the Northern and North Central Provinces where their ranges meet. Phillips in his "Annotated Checklist .." (1978), Ali & Ripley in their "Handbook ..." (1983), Ripley in his "Synopsis ..." (1982), Wijesinghe in his "Checklist ..." (1994) and all later authors follow this pattern, but the scientific names of the Ceylon Golden-backed and Red-backed Woodpeckers are now Dinopium bengalense jaffnense and D. b. psarodes respectively.

Based on  these works, the current opinion is that the Ceylon Golden-backed and Red-backed Woodpeckers are two endemic subspecies of the Indian Lesser Goldenback Dinopium bengalense, or Black-rumped Flameback of modern nomenclature. As far as the distribution is concerned, jaffnense is described as a common breeding resident in the northern dry lowlands, while psarodes inhabits the southern lowlands and hills, with hybridisation taking place where the ranges meet (Wijesinghe 1994). Earlier authors mention a line from Puttalam in the West to Trincomale in the East where both species integrate (Phillips 1978). However, Legge (1883) suggests that already in earlier times, the range of the Red-backed Woodpecker has extended much further north than this line and than hitherto assumed.

CBCN Evaluation Results

A recent evaluation study of the CBCN, however, shows a somewhat different picture. When during the regular 20 years study period of 1981-2000 new evidence began to emerge, the research was extended to the 50 years period of 1956-2005 in order to establish a wider and more reliable data base. The results are capable of modifying the prevailing views on the distribution and status of the two woodpeckers.

As stated before, the distribution range of jaffnense is generally assumed to extend southward to a line from Puttalam on the west coast to Trincomalee on the east coast, and the northern end of the range of psarodes to coincide with the same line. This position is no longer true. The present evaluation indicates that the main southern limit of the range of jaffnense extends to about N 7°20' on the west coast and to about N 8°30' on the east coast, which is roughly a line from Negombo to Trincomalee. On the west coast, the species has once even been recorded as far south as N 7°13' (near Katunayake), while the northern range of psarodes extends to about N 8°35' (roughly a line from Marichchukkaddi to north of Trincomalee). Thus, there is a wide belt of overlapping occurrence along the north-western coastal areas.

Special attention is therefore drawn to the west coast of the northern dry zone. From the comments by the early authors (Legge, Wait, Baker, Whistler), one can infer that in earlier times the Red-backed Woodpecker was absent from this area, its place being taken by the Golden-backed. However, the present study reveals that the situation has changed fundamentally. The Red-backed Woodpecker is now a regular resident there, alongside with the Golden-backed.

Already Wijesinghe (1995) in his distribution study of the Woodpeckers in Sri Lanka points out that the ranges of the two forms are not mutually exclusive, as on the west coast both forms exist over a fairly extensive area from about Negombo to Wilpattu, and this area of overlap probably extends considerably inland. The present study clearly confirms this situation and suggests, that particularly in the Chilaw area where both species are relatively common, there is sympatric occurrence with no perceptible tendency to interbreed.

Some uncertainties exist in respect of the northern inland forests where intermediate, reddish-orange individuals are known to occur. These may either be natural forest variants of the Golden-backed Woodpecker as assumed by Legge and other authors and as known from the Indian race puncticollis (Baker 1927, Whistler 1949), or perhaps be hybrids of the Golden-backed and Red-backed Woodpeckers as first claimed by Whistler (1944) and accepted by later authors.

When reading through the works of the earlier authors (Legge to Henry), one gets the impression that in the northern forests, intermediate, reddish-coloured birds were common at that time. The present evaluation, however, suggests that - perhaps as the result of progressing forest clearing - the occurrence of both the Golden-backed and the Red-backed Woodpeckers is sparse in this area, and intermediate forms are rare. During the 50 years survey period, only 8 reports with a total of 9 "hybrid-type” birds are found in the Notes. Six of them were recorded in the northern inland forests, two in the northwestern and one in the northeastern coastal area. Most of these reports date from the 1960es, 70es and early 80es. While the majority refers to birds with an orange back, one report of May 1990 from Anuradhapura describes a pair with golden backs partly speckled red. In 2 of the 9 "hybrid" records, no colour features are mentioned.

In one bird from Anuradhapura, the back colour is described "not pure golden, but a mix of gold and dirty green". This is certainly not a case of hybridization, but corresponds to the description of Wait (1931) as "golden-olive" of portions of the wing coverts and outer webs

of the secondaries, and also that of Ali & Ripley (1983) who refer to the "olive wash" on both mantle and wings.
Today, there are good reasons to question again the hypothesis of interbreeding. In fact, from all known literature including the CBCN 1956-2005, it appears that nobody has ever seen a mixed pair breeding and raising young, and consequently there has never been a description of the features found in the descendants of possible mixed pairs. So far, evidence of inter-breeding is exclusively based on the (rare) occurrence of orange, reddish-tinged and reddish speckled birds which are assumed to be hybrids.

Somewhat uncertain is the situation in northern inland forests. Although it is not known whether pure golden-backed and red-backed birds interbreed there or live in sympatry as they do in coastal areas, there is evidence that the latter is the case. One observer claims that in the Anuradhapura-Dambulla-Nochchiyagama triangle, both forms are quite common, seen in roughly equal numbers (CBCN 84: 28). Indeed, the majority of reports from inland areas clearly refers to either golden-backed or red-backed birds, and apart from the record of the two birds with speckled scapulars (the only such record in the Notes), only one other "hybrid" has ever been recorded from the Anuradhapura area within the 50 years survey period. This suggests that in general, the two Woodpeckers probably do not mix in inland forests. If free interbreeding would take place as hitherto assumed, this would sooner or later result in the extinction of pure golden-backed birds and/or in a noticeably greater number of intermediate, "hybrid-type" forms within the areas of overlapping occurrence. However, occasional interbreeding especially between reddish-coloured Goldenbacks and the Red-backed Woodpecker in northern forests can not be completely excluded. This is supported by the fact that the amount of red in the "hybrid-type" birds may vary considerably, being very distinct in some individuals. However, the low number of "hybrids" reported within 50 years (with only 2 such reports after 1990) shows clearly that if interbreeding is taking place, it must be the exception and not the rule.
Most "hybrids" are said to occur in the Wilpattu NP, but during the 50 years study period there are only 3 such reports in the Notes, all prior to 1981. During the same period of time, only 3 Red-backed Woodpeckers were seen there. From the re-opening of the park in 1998 until the end of the study period in December 2005, several Golden-backed but no Red-backed Woodpecker or "hybrid" has been reported from the park. There is, however, a recent report of one bird which appeared to be a Red-backed Woodpecker from Mannar Island

Some reports in the CBCN refer to interacting Golden-backed and Red-backed Woodpeckers, seen together "as a pair". However, such records are not evidence of interbreeding. Various kinds of Flamebacks and other Woodpecker species, male and female, have been seen together searching for food without being pairs. In one case, a pair each of the Golden-backed and Red-backed Woodpeckers was observed chasing each other from palm to palm. This could well be a case of competition for territory between the two species.

Surprisingly, there are a few reports of the Golden-backed Woodpecker from the eastern and southern dry zone in the Notes. One bird was reported from the Wasgomuwa NP (CBCN 1998: 26), two from Debarawewa/Tissa (CBCN 1982: 27), and one from Wiraketiya (CBCN 1964: 32), and a possible one from the Uda-Walawe NP (CBCN 1993: 25). However, these records appear somewhat doubtful and may perhaps result from a confusion with the White-naped Woodpecker Chrysocolaptes festivus. They are therefore in need of confirmation.

Summary

Contrary to the prevailing opinion, the evaluation of the CBCN 1956-2005 suggests that the Ceylon Golden-backed Woodpecker largely coexists in sympatry with the Ceylon Red-backed Woodpecker, and does not freely interbreed as hitherto assumed. This is especially true of the Chilaw area where both species are relatively common.
Although occasional interbreeding may be possible, mixed pairs have never been seen breeding, and the descendants of possible mixed pairs have never been scientifically studied and described. Hybridisation is only assumed on the basis of sight-records of "hybrid-type" birds, and from the scientific point of view, this is merely a hypothesis. Only nine such "hybrids" have been documented in the Notes within the 50 years survey period, most of them prior to 1990. The majority of these is described as having orange backs. Two golden-backed birds had the upper portions and scapulars speckled red, and one had the back reddish gold. In two reports, the back colour is not mentioned.  Nothing is known on the reproduction capability of possible "hybrids", and finally, the question of natural variants of the Golden-backed Woodpecker with reddish-tinged backs still remains open.

Statistically, the 9 "hybrids" - if really such - reported within the 50 years study period make only one such report every 5½ years. This is by no means unusual in ornithology. Many closely related bird species are known to hybridize occasionally. Worldwide, roughly 10% of all bird species are involved in hybridization (Grant 1992).

Modern conditions for assigning species rank lay down (among other criteria) that hybridization occurs at such a low frequency, that it is unlikely that their gene pools will ever merge (Helbig et. al. 2002). This is obviously the case with  the Ceylon Golden-backed and the Red-backed Woodpeckers. Further, hybrid zones which are stable over time, narrow and in which phenotypically pure individuals make up a considerable proportion always indicate a distinct barrier to gene flow; they often involve unisexual sterility which in birds affects the female sex (Helbig 2000). Thus it seems that a gene flow barrier is very likely to exist between the two woodpecker species. The sympatric coexistence over wide areas as well as the low number of "hybrid" reports in recent years clearly indicate the existence and perhaps the further development and strengthening of such a barrier.

Basically, the results of the present evaluation study suggest that the two Sri Lankan Woodpeckers occur in sympatry and behave as two separate species, with no or little tendency to hybridize. Consequently, and in accordance with the criteria of species ranking mentioned above, the Ceylon Red-backed Woodpecker would deserve the status of a "full" endemic species Dinopium psarodes which it used to have in earlier times (with different scientific names). For the time being, it could however well be treated as a semi-species Dinopium [bengalense] psarodes pending the definite resolution of its status. Meanwhile, the status of the Ceylon Golden-backed Woodpecker remains unchanged, as subspecies jaffnense of the Indian Lesser Goldenback Dinopium bengalense.

All conclusions of the present paper are based on the Analysis and Evaluation of the Ceylon Bird Club Notes 1956-2005 and therefore are in need of further field studies. In addition, it is suggested that ornithologists and birdwatchers pay special attention to the two Woodpecker species, their sympatric coexistence and possible hybridization within the area of common occurrence. Moreover, it is recommended to look out for the possible occurrence of the Golden-backed Woodpecker in eastern and southern dry lowlands.

Acknowledgement:  I am very grateful to Mr. T.W. Hoffmann and Mr. Udaya Sirivardana for their kind assistance.

References

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