Friday, December 17, 2010

Sabah: Bristlehead Tower, Without Bristleheads

Of all the birds in Borneo, the one that I have been most anxious to see is the Bornean Bristlehead (Pityriasis gymnocephala), a peculiar bird of uncertain affinities now placed in its own family.  Naturally, it has been my greatest jinx.  The Bristlehead is a wanderer, never certain anywhere.  If there is any place where you have a reasonable chance of seeing it, it is along the canopy walk at the Rainforest Discovery Centre at Sepilok, near Sandakan in eastern Sabah.  

So when Eileen and I travelled to Sabah the RDC was a necessary stop.  In fact, I spent two hot, sweaty mornings there, on May 1 and 5, pounding the beat between the mockingly-named Bristlehead Tower and its companion Trogon Tower.  And, of course, there was not a Bristlehead to be had.

At least the towers provided some shade!

Heat, and an absence of Bristleheads, aside, the canopy walk was a rewarding experience - not least because it is a sturdy steel structure, so I could concentrate on my surroundings rather than succumbing to panic every time it swayed (as I tend to do in traditional wood-and-netting canopy walks).  And the forest around me was very beautiful.

This is typical lowland rainforest, dominated by trees of the family Dipterocarpaceae, a group that reaches its height of diversity in Borneo where there are some 267 species.  Dipterocarps in Sabah were in the midst of a mass fruiting during our visit, something that only happens every few years, and some of the trees along the walkway were putting on an impressive display.  "Dipterocarp" means "two-winged fruit", and you can see the reason for the name in this photo.  The fruits of most dipterocarps are vaguely like maples, with two long wings that catch the air and set them, when they fall, spinning in the wind like miniature helicopters -- an adaptation that helps them disperse further from the parent tree.

The diversity of plant life in the forest canopy is staggering -- 

I only wish I had had a botanist with me to tell me the names of the plants!

The bright colour of these leaves -- a common sight in rainforests throughout the tropics -- probably signals that, though they may be young and tender, they are probably full of toxic chemicals and are best not eaten.

This impressive pair of leaves on the ground beneath the Trogon Tower probably belongs to a species of aroid, the plant family that includes taro, jack-in-the-pulpit and a host of tropical plants.

Bird activity in general is best early in the morning, but the heat of the day holds no terrors for sunbirds.  Here are two species, both females (or young males).  First, a Purple-naped Sunbird (Hypogramma hypogrammicum), a bird that normally prefers the lower levels of the forest (but can show up anywhere)...

And here is a female Crimson Sunbird (Aethopyga siparaja). The illustration of this plumage in Susan Myers' otherwise excellent Field Guide to the Birds of Borneo shows the throat and upper breast yellow instead of greyish; the text gets it right, though.

An Oriental Pied Hornbill (Anthracoceros albirostris) flies high over the canopy...

While, within its depths, a Green Iora (Aegithina viridissima) forages quietly.

As everywhere in Malaysian forests, there are always bulbuls.  This is a Buff-vented Bulbul (Iole olivacea).

Bulbuls can be hard to identify.This is an Olive-winged Bulbul (Pycnonotus plumosus); the upper photo shows its streaked cheeks and buffy undertail coverts.

The canopy walk was also an excellent place to watch squirrels. This Prevost's Squirrel (Callosciurus prevostii) was just a little too shy and fast-moving for me to get a decent photograph.  The Sabah race (C. p. pluto) lacks the distinct white side-stripe of the animals around Kuching.

I had much better luck with this spectacular creature, a Giant Squirrel (Ratufa affinis). I have seen Giant Squirrels before, but they are usually shy denizens of the canopy and this, at the Trogon Tower, was the first time I had encountered one at eye level. It made me appreciate just how big Giant Squirrels are – about the size of a house cat, not counting the extraordinary tail (32-38 cm for the head and body, with another 37-44 cm for the tail, according to A Field Guide to the Mammals of Borneo, some twice the size and weight of Prevost's Squirrel or a North American Grey Squirrel).

The most spectacular bird along the walk, absent the Bristlebirds, was this highly cooperative Banded Broadbill (Eurylaimus javanicus) busily gathering long strips of bark for its nest.  Broadbills are extraordinary, artificial-looking creatures, members of an ancient lineage with an impressive evolutionary history (besides the "typical" broadbills of Africa and Asia, the family now includes the very different-looking sunbird-asities of Madagascar and even a previously unsuspected outlier, the Sapayoa (Sapayoa aenigma), in South America). 

The nest itself was an ungainly-looking mass of twigs, bark strips and plant fibres, but what it may have been lacking in aesthetics it more than made up for in cleverness of placement.

Here you can see why the bird chose this particular nest site.  That fearsome-looking object right above it is a hive of Giant Honeybees (Apis dorsata), large and aggressive insects that might make any nest predator think twice before interfering with the broadbill's home life.  One scientist has described the Giant Honeybee as one of the most dangerous animals of the Southeast Asian jungles.

Borneo is particularly rich in honeybees - five of the nine known species occur here.  The bees have recently been the subject of a book, Honey Bees of Borneo: Exploring the Centre of Apis Diversity by Nikolaus and Gudrun Koeniger and Salim Tingek (Natural History Publications (Borneo), 2010), that takes you into their lives and makes a plea for their conservation.  Giant Honeybees, as the photos show, build their nest in the open, protecting the contents with a curtain of living bees.  The bees line its walls, armed with long stingers and virulent toxins, and defend it against all comers.

Nonetheless, on my second visit a few days later I saw that something had managed to breach the colony's defenses and destroy a good part of the hive (note, though, that the broadbill's nest appears none the worse for wear).  What it was I don't know, but Oriental Honey Buzzards (Pernis ptilorhynchus) are known to make lightning attacks on Giant Honeybee colonies, ripping off chunks of the hive and dashing away with them before the bees can react.  It's probably a good thing that I wasn't there to see whatever happened; after an attack on a hive in their garden, the Koenigers were unable to leave their house for hours for fear of the enraged insects.

A couple of good mornings, then, after all.  As for the elusive Bristlehead -- well, better luck next time!

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