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Plainly Plain...A Memorable Afternoon When 718 Hornbills Passed by

The Plain-Pouched Hornbill of the Malay Peninsular

By Glenda Noramly

Reproduced from "Suara Enggang", a bi-monthly bulletin of the Malaysian Nature Society

We were climbing the steep skid trail in a logging concession at the time. The weather had been wet all morning, drizzling rain, and had stopped about an hour earlier. The others in the group lagged behind to examine a cleared area where a tree had been felled, and I walked on up to the top of the ridge. Standard fare: a party of Brown Fulvettas, a couple of Yellow-bellied Warblers, a sallying Dark-sided Flycatcher, a noisy Greater Raquet-tailed Drongo. And then the sound that makes all bird watchers jerk their heads upwards: whoosh-whoosh-whoosh…the unmistakable steam-train approach of flying hornbills. And I was stuck under an unbroken canopy!

Frustrated, I just had to wait while a group of seven or so flew past-wonderfully low-and I was unable to even guess at their identity. I kept my fingers crossed that the others (none of them out-and-out birdwatchers and most without binoculars) would count them and pick up enough pointers for identification. And then, no sooner had the whooshing sound died away, than another group was heard-and another, and another, and another…

I tackled the downward slope at neck-break speed, heedless of the fact that rain had made it as slick as a bob-sled shute. I arrived at the cleared area mercifully intact and just in time to raise my bins and fix on the very last bird in a group before it disappeared behind the trees: and there it was-white-tailed, black-winged--and with a smooth bill and unmarked pouch of ivory colour,both as bare as the proverbial baby's bottom. It was a Plain-Pouched Hornbill Rhyticeros (Aceros) subruficollis.

It was November 19th 2001 and we-Dionysius Sharma, Mohd Azlan Jeyasilan, and botanists Wong Khoon Meng and Philip Lepun-were in the Temengor Forest Reserve Perak, close to the Kelantan border, several kilometres south of the East-West Highway. This area borders the Lower Belum Forest Reserve, and the logging concession is in the heart of the main range. We were at an altitude of about 560m.

Ever since the first MNS Belum expedition produced massive numbers of over-flying hornbills in 1993, I had dreamed of seeing such a thing. And how much more, when it was proven that at least some of the massive subsequent flocks seen in the area were actually Plain-pouched Hornbills, a supposedly Thai-Burmese species. (Anyone wishing to read an article summarizing this enthralling story is advised to see Allen Jeyarajasingam's article in the Suara Enggang No 2, 2000 p26ff). I had been to Temengor on numerous occasions, and seen no more than a few isolated hornbills of the more usual species. Fortunately the 80 birds which had passed while my view was blocked were just the beginning.

In the next hour and twenty minutes a total of 718 hornbills passed low overhead between 1415 hrs and 1535 hrs, of which a good proportion were Plain-pouched. Not quite as many as the largest recorded flypasts of over 2,400---but believe me, we felt like kids in a candy shop-that's an average of one bird every 6 or 7 seconds! Even the botanists forgot about botanizing.

The birds were travelling from NW to SE, and may have crossed over the next range of hills (over 1000m) into Kelantan. They passed in groups varying from two or three single birds to chevron skeins of more than twenty. The most common group size was 5 to 7 birds. Ratio of male to female to immature was very approximately 3:3:4 (but see below). They crossed on a broad front, and we may in fact have missed counting a number of groups because the distant view in both directions was blocked by trees. Two birds, one male and a female, perched for a brief time in a tree directly over our heads. A few other birds perched briefly in a nearby tree, and called before proceeding on. Details of appearance were not easy to ascertain because of our hemmed-in position--we could observe through gaps in the canopy, either directly above, or-because of the steep slope--just higher than eye level, but only for brief periods of time as birds crossed the gaps. A frustrating situation for a birdwatcher, and there were many details I missed as a consequence.

About 5% of the birds observed were seen only to be hornbills, without any other features distinguishable. The remainder were clearly identifable as Rhyticeros (Aceros) spp, and all those that were positively identified (perhaps 10-15%) were Plain-Pouched. It is possible that not all groups were this species-in fact, several groups were tentatively suspected to be Wreathed, and one male and female pair of Rhyticeros (Aceros) spp that flew past further away (and may not have been part of the general flight) seemed to have a larger casque on the male, with a lot of bright red in the casque/beak base area. I thought at the time they might be Wrinkled (although the species is a flatland specialist), but decided I must be wrong. What would they be doing at this altitude? However, in January 02, a pair of Wrinkled was seen even higher up the logging road, so I now believe they were this species.

I would very much like to know more about pouch/bill colour of the Plain-pouched during breeding! Do they ever go rosy, or even orange? According to literature, the base of the adult male's beak is a dull dark red at best, and many of those seen were indeed this colour. The following features on the Plain-pouched were noticed:

short white tails, all black wings, pale bills with low casque. No corrugations on the bill, although this was sometimes hard to be sure about on some adults, because of the darker coloration on the bill base. No marks on the pouch. Strong wingbeats that produced a whooshing sound. Only twice were individual birds noted to glide. One of these, passing overhead, glided for a short time and the sound whistling through the wing feathers during the glide was noted to be different to the sound produced by wingbeats.

Females were noticeably darker than males, having no white on necks and heads and having blue (and therefore darker) pouches.

It was easier to be sure about the identification of males rather than females because it was easier to see that there was no black band on the paler-coloured pouch. The size and colour of male pouches varied: some had pouches that were ivory pale in colour, others-especially the larger ones--were bright yellow, and some (a few large ones) were almost reddish-orange, especially in the folds near the head and neck. Literature does not remark on this reddish-orange colouring-could it possibly be a phenomenon of breeding?

The immatures (?) were easier still to identify because the bills seemed to lack the dark bases, and bills and pouches were pale ivory or bone-coloured and therefore easily seen to be plain and unmarked. (Note: Because casque size is not large even in adults, it was easier to use the very pale and small-almost flatish pouches as an indication of immaturity-but this observer is not sure about the reliability of this method! It could just be the appearance of non-breeding birds…). Oddly enough, Ho & Sutari (1997) reported a higher ratio of females to males (1.2:1).

Literature suggests that Plain-pouched have a three note call in flight, whereas Wreathed Hornbills make a double note call (although 3 note has also been recorded). However a member of the Thai Hornbill Project told me that he couldn't tell the difference between the two species by sound alone (Narong Jirawatkavi pers.comm.). Most of this fly-past was silent except for the sound of wing beats. Some unseen birds which perched briefly were heard calling--single grunts and a double note call. Then there was the last bird to pass close by, which also called in flight. The sky was empty of birds when this unidentified female, presumably trying to locate the remainder of the flock, gave several spaced two-note calls, and then followed this with a three note call. My scribbled field notes render this as w-wup on a rising intonation, and w-w-wup, also lilting on the final note. It is my belief the calls were less booming than the Wreathed, and are well described in Birds of Thailand as "higher-pitched, more quacking" than the Wreathed. However, my experience with the call of the Wreathed is not that extensive either!

718 hornbills in flight is a sight I will never forget. I hope it is something that those who come after me in years to come will be able to see it too…but sometimes I wonder. Virtually nothing is understood about these two enigmatic species, the Wreathed and the Plain-Pouched, and we may already be doing things that will ensure their demise.

Where do they nest? No nests have ever been found in Malaysia! A flock of about 900 was once seen in S.Thailand near the border, and certainly large flocks have been identified in Malaysia-but they seem to arrive and disappear mysteriously, without ever having done anything as prosaic as nest and raise young. Now there's a mystery for you.

References
  • Davison, G.W.H., (1995). The Birds of Temengor Forest Reserve, Hulu Perak, Malaysia Mal.Nat.J., Vol 48 Parts 3 & 4.
  • Ho Hua Chew and Sutari Supari (|1997). Spectacular Movements of Hornbills, possibly Plain-pouched Hornbills Aceros subruficollis, in Peninsular Malaysia. OBC Bulletin No 25 June 1997.
  • Kemp, A., (1995) The Hornbills-Bucerotiformes. Bird Families of the World. OUP, Oxford.
  • Jeyarajasingam, A. (2000), Report of the MNS-BCC Records Committee March 2000, Suara Enggang, No 2, 2000.
  • Rasmussen, P.C. (2000). A review of the taxonomy and status of the Plain-pouched Hornbill Aceros subruficollis. Forktail 16 : 83-91.
  • Wells, D.R., (1999) The Birds of the Thai-Malay Peninsular Vol. One. Academic Press, Lond.
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