ASK THE EXPERTS

In this new feature of eBON, WBCP members are encouraged to ask a bird-related question to be answered by the experts. WBCP member Randy Weisser asks the experts how to distinguish between the crow species.

A Guide to the Birds of the Philippines by Robert Kennedy et al is the usually the first book that people reach for when looking for information on Philippine birds as it is the definitive field guide for Philippine birds. However, there are times when even a careful reading of the Kennedy guide still leaves a birder full of questions and looking for more information. At these times, a great source of information are the experts who have spent a lot of time in the field observing birds.

WBCP member Randy Weisser asks this month’s bird identification question. The three bird experts consulted are:

  • Oriental bird specialist Desmond Allen
  • BirdTour Asia Director Robert Hutchinson
  • Bird guide and blogger Mark Villa

Randy Weisser asks:

I am attaching an audio file of a crow.  I would be interested if this call could be conclusively definitive of one species.


Recording of a crow by Randy Weisser.

From Desmond Allen:

The attached call is typical of Large-billed Crow and unlike any of the recordings I have heard of any other Philippine crows. But this species also makes many other calls – but, again, different from the other species.

Randy Weisser asks:

I am interested in hearing from the experts what is most helpful for them in distinguishing between the two crow species. The features given in Kennedy are mostly slight differences between the two species but it seems that they are rarely seen together to make the comparisons.  I am wondering if there are any other tips or elaborations that the experts can share other than what Kennedy mentions.

editor’s note: the Kennedy guide mentions differences in the call, size, bill size, and flight.

From Desmond Allen:

As always, you need to read the main text of the Kennedy guide and not just the plates, but in this case it may be hard to make a correct ID.

There are at least 3 or 4 species of crow in the Philippines: the Sierra Madre crow in northern Luzon Corvus (enca) sierramadrensis, the Samar/Mindanao crow Corvus (enca) samarensis, the Palawan/’Slender-billed Crow’ Corvus (enca) pusillus of Palawan/Mindoro, and the ‘Large-billed’ Crow Corvus macrorhynchos philippinus. I believe that bill size and flight pattern as indicated in the Kennedy guide may sometimes be a useful indicator but often it is misleading. Large-billed can fly with its wings held below horizontal, for example, and pusillus doesn’t seem to have a clearly different bill from some Large-billed. Also, the head shown for Slender-billed for example on plate 49 is not dissimilar to immature Large-billed, often seen well at Subic, for example.

Large-Billed Crow from Subic. Photo by Sylvia Ramos

Slender-billed Crow from Palawan Photo by Neon Rosell II

Large-billed Crow from Subic, full body. Photo by Sylvia Ramos.

Slender-Billed Crow from Palawan, full body. Photo by Neon Rosell II
From photos by Rob Hutchinson (see photo below from Mt. Dos Cuernos) and Mark Villa (see photo below from Sierra Madre) it appears to me that Sierra Madre crow has bare skin behind the eye that Large-billed lacks, is smaller with a proportionately larger head and a deeper, shorter bill. James Eaton’s photos of samarensis (see photo below from Samar) seem to show a bird similar to this. I haven’t been able to study museum skins of either sierramadrensis or samarensis though, as there are none in the UK. Skins of crows at the BM(NH) at Tring labelled as pusillus from Palawan are indistinguishable from Philippine Large-billed though!According to McGregor (Manual of Philippine Birds, 1910) Mindoro/Palawan Slender-billed is much smaller than Large-billed (wing = 250 v 314mm), and Samar Slender-billed even smaller still (wing = 220mm). McGregor also gives some useful tips in details of the feather lengths. For the Slender-billed Crows he writes (p723): First primary decidedly shorter than the outer secondaries, the latter longer than any of the interior ones; tail very slightly rounded and shorter than the longest secondary. While for Large-billed: First primary about equal in length to the outer secondaries, the latter shorter than some of the more interior ones; tail much rounded and about as long as the longest secondaries

In this case I am sure the first primary is the innermost primary. You can see the effect in Mark’s photo of a Sierra Madre Slender-billed:

Sierra Madre Crows by Mark Jason Villa.

Video grab of Slender-billed Crow in flight by Desmond Allen


Video of flying Mindoro Slender-billed Crows by Desmond Allen.

Large-billed should have a much straighter trailing edge to the wing, unless the wings are being held back, and  the tail should appear rounded unless it is closed up.
Large-billed Crow. Video grab by Desmond Allen.


Video of a flying and calling Large-billed Crow by Desmond Allen.

However, calls are the best way to distinguish them. Large-billed has the waak calls that you are used to but also many less common calls. The KG says of Slender-billed Crow (p243), “Some have suggested that the subtle differences in voice and perhaps habits imply that more than one species may be involved in the Philippines.” However, to my ear, the Palawan-Mindoro crow is clearly different in calls from Slender-billed of Borneo, and the Sierra Madre crow is much different again.

Palawan-Mindoro/Slender-billed crow has a rather frog-like call given in short phrases, (check Xeno-Canto) like a steel comb being quickly and repeatedly scratched, and it seems to modulate its basic call presumably to convey different meanings. Meanwhile the nearby Borneo birds have a lower, longer, buzzing waak call, more similar to Large-billed; Sierra Madre crow has typically higher-pitched calls that are rasping but not obviously buzzing, and may inflect upwards strongly.


Sierra Madre crow
recording by George Wagner and posted in Xeno-Canto and shared under the Creative Commons Attribution-NonCommercial-NoDerivative Works licence. Click on play to listen to the call.


Another  Sierra Madre crow recording by George Wagner and posted in Xeno-Canto and shared under the Creative Commons Attribution-NonCommercial-NoDerivative Works licence. Click on play to listen to the call.


Recording of a Sierra Madre crow from Minuma, Isabela by Desmond Allen

As for field ID, where are you? Are you in open country, or in or very near pristine forest? If the latter, and you are in Luzon, it could be Sierra Madre crow. However, this is a poorly known bird and seems to be rare. Any records away from Hamut Camp are interesting so please back them up with sound recordings (and close HD video 🙂 ) I am not familiar with the Samar/Mindanao crow, but again it is poorly known and seems to be rare so lots of details of any sightings would be much appreciated.

The Kennedy guide says the nest and eggs of Slender-billed Crow are unknown – apparently even of the fairly common Palawan pusillus crow. We really need to understand the habits and requirements of the Sierra Madre and Samar crows in order to be sure we are conserving the right aspects of their habitat. Readers, please take note!From Robert Hutchinson:

Unfortunately the identification of these crows isn’t straightforward and a number of features and factors need to be considered.

The first thing is that the three forms of ‘Slender-billed Crow Corvus enca’ as described by Kennedy are in my opinion three species; the birds on Palawan/Mindoro Corvus (enca) pusillus which are often referred to as Palawan crow (not a great name for a species equally common on Mindoro?), those in Greater Mindanao Corvus (enca) samarensis usually referred to as Mindanao crow and those in the Sierra Madre Mountains Corvus (enca) sierramadrensis best called Sierra Madre crow. I have studied museum specimens of many of these birds together with those elsewhere from Asia and of course the main confusion species; Large-billed Crow Corvus macrorhynchos philippinus and have seen all in the field but they are certainly not an easy group to separate.

All three ‘Slender-billed’ species look rather alike but since they are all on different islands it isn’t significant for us and their respective separation from Large-billed Crows relies on the same features in each case.  All are smaller, noticeably shorter tailed, larger headed and with a shorter bill than Large-billed Crow but these features are difficult to judge in the field without lots of experience or direct comparison of the two species and should be used with great caution. In addition sierramadrensis and samarensis always seem to show a bare skin patch behind the eye but this is very difficult to distinguish unless views are very close because the feathers on Large-billed can often lie in a way that looks like a similar patch and unless good photos are taken this should only be a supporting feature. Although the three ‘Slender-billed’ crows all have a distinctive flight with shallow wingbeats, usually below the horizontal plane, Large-billed can also fly in this way so is not a reliable separating feature. Habitat is probably only a useful separating factor on Luzon where Sierra Madre crow should only be found in good forests of the Sierra Madre Mountains well away from the open country habits of Large-billed Crow, as far as we know both species can occur together on Palawan/Mindoro and Mindanao/Samar.

Sierra Madre crow from Mt. Dos Cuernos. Photo by Robert Hutchinson

Corvus (enca) samarensis from Samar, photo by James Eaton.

Corvus (enca) samarensis from Samar, photo by James Eaton.

If you read up to this point then all might seem hopeless but fortunately the distinctive calls of all three ‘Slender-billed’ Crows allows them to be separated from Large-billed Crow with practice. It is also preferable that records should be supported by sound recordings in the case of out-of-range Sierra Madre Crow and all incidences of Mindanao crow. Listening to the calls linked below will certainly help!

The Large-billed Crow has  varied calls including loud ‘wark wark’ notes and the starting point for finding the other crows is to learn the calls of this commonly encountered species.

Recording of a Large-billed Crow in Pasonanca Watershed, Zamboanga by Robert Hutchinson

The Palawan / Mindoro crows have a distinctive ‘croaking’ frog-like call which is very different from Large-billed Crow.


Recording of a Palawan crow from Mindoro by Robert Hutchinson


Recording of a Large-billed crow from Mindoro by Robert Hutchinson

The Sierra Madre crow has a distinctive series of higher pitched, upwardly inflected calls that often rise in pitch during the calling series. If you are lucky enough to see calling birds pay attention to the amazing wing-raising that accompanies each call note in this species!


Recording of a Sierra Madre crow from Mt. Dos Cuernos by Robert Hutchinson

Likewise the Mindanao crow Corvus (enca) samarensis can be separated from Large-billed Crow by virtue of its longer, higher pitched, more buzzing call notes


Recording of Mindanao crow Corvus (enca) samarensis from Samar by Robert Hutchinson

Unfortunately little is known about these birds and their habits and while the Palawan /Mindoro birds are common and widespread, Sierra Madre crow is scarce even in good forest and all records should be well documented (especially those sounds) so that we can know exactly where they occur. Mindanao crow Corvus (enca) samarensis is of particular interest because it seems to be rare and might possibly require good lowland forest, in which case they are likely endangered and it is important that any records are carefully documented because when the ‘Slender-billed’ are split into three, this will go from being ‘just another slender-billed’ to one of the most threatened  birds in the Philippines! Again please help us to find out more about these fascinating birds by making recordings of the sounds of any potential candidates where possible.

From Mark Jason Villa:

I am no expert as I’ve seen the Slender-billed Crows in Luzon only twice. I am not sure actually if there are Slender billed crows in Luzon outside of the Sierra Madres.

The Sierra Madre crows when seen well enough are quite distinctive from the Large billed Crows. It seems to be a smaller bird with a disproportionately big head compared to its body. It also has a distinctive bare patch behind the eye. Large billed crows have a proportionately smaller head compared to its large body. The vocalization is also very different. From memory, I heard a continuous werp werp werp call much less harsh than that of Large-billed Crows. Slender-billed Crows in Palawan are much more similar looking to Large-billed Crows than the ones in Sierra Madre but also sound different, almost like ducks quacking.

Sierra Madre crow. Photos by Mark Jason Villa

compiled by Sylvia Ramos

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