Most birders know that the female hornbill seals herself inside a tree cavity when she is ready to lay her eggs. But how many have actually witnessed the hornbill breaking out of its cavity when the chicks inside are ready to leave the nest?

Let alone document the stages?

It has to be left to a photographer to undertake the assignment. Dr Eric Tan, an avid nature (bird) photographer, was at Pulau Ubin at the right time when the female Oriental Pied Hornbill (Anthracoceros albirostris) was breaking out of her nest. He meticulously documented the various stages and is here sharing them with everyone.

When the female is ready to lay her eggs, she enters the nest cavity, usually in a tree trunk. The male then brings her mud that she mixes with her faeces and mashed fruits to seal the entrance until only a narrow opening is left (above).

The female then begins to pull out her wing and tail feathers and then lays her eggs. The male will, in the meantime, delivers food for her and her chicks (above).

Once the chicks are ready to fledge, she will start breaking out of the cavity. This seal is then brick-hard and generally impenetrable from the outside. She needs to use her bill like a pickaxe to slowly break down the seal. As the seal slowly breaks down and the entrance enlarges, she needs to squeeze herself out. First her large bill and casque appear, then her head pops out (above, top row). Next, one of her shoulders pushes out, followed by the wing. Once one of her wings is free, she emerges partially before becoming totally free to immediately fly off (above, bottom row).

The chicks will then be enticed to leave the nest by the adults not bringing them food. As the chicks are not of uniform age when the female breaks out, the questions that need to be answered are: 1. Does the female re-seals the nest? 2. Do the chicks take over the job? 3. Is the entrance left unsealed? 4. Who returns to feed the remaining chick/s, the male or the female? There is obviously a need for further observations.

The sealing of the female inside the cavity provides security from predators, prevents the nesting cavity from being flooded and keeps off competitors – other hornbills that may otherwise try to evict the occupants for their own use. However, Kinnarid & O’Brien (2007), “…believe that nest-sealing evolved as a female strategy to ensure male fidelity.” With the male kept busy foraging for himself as well as for his mate and later the chicks, he would have no time to indulge in extra-pair copulations or maintain another female sealed in another cavity.

Reference:
Kinnarid, M. F. & O’Brien, T. G. (2007). The ecology and conservation of Asian hornbills: Farmers of the forest. University of Chicago Press.

This post is a cooperative effort between NaturePixels.org and BESG to bring the study of bird behaviour through photography to a wider audience.

In a talk to update the public on the Singapore Hornbill Project on 22nd May 2008, Marc Cremades, who initiated the project together with Prof Ng Soon Chye, announced that the population of the Oriental Pied Hornbill (Anthracoceros albirostris) in Singapore has seen a sudden explosion.

These large and impressive birds have been slowly increasing in number over the last decade or so. When the project was initiated in 2006, the hornbill population was below 30 birds, with about 20 in Pulau Ubin.

The use of nesting boxes in the offshore island of Pulau Ubin has contributed to this sudden increase in population. The birds have been accepting these nesting boxes and using them to breed, and to raise a number of chicks successfully (top).

According to Marc, there are at least seven breeding pairs in Ubin and about 19 juveniles around. He estimates that the total population for Singapore is around 50.

Soon, these artificial nesting boxes will be tried on mainland Singapore. And hopefully, more Singaporeans will get a see these large and impressive birds.

The Bird Ecology Study Group is proud to be associated with the Singapore Hornbill Project.

The above image is courtesy of the National Parks Board, Singapore.

Ben drew my attention to the 2004 special issue of the journal, Bird Conservation International. This special issue, dedicated to the conservation of hornbills, carries some of the many papers read at the Third International Hornbill Workshop held in Phuket, Thailand in 2001.

Ben e-mailed me, “I just came across a bit of interesting trivia from an introduction page of a special supplement of Bird Conservation International dedicated to the conservation of hornbills… Dec 2004. Vol 14 Supplement S1:S3. The excerpt that caught my attention was this:

“’This volume is dedicated to the memory of Elizabeth Glassco Hudson (1956– 2002). One of Lis’ most powerful and exhilarating experiences was in Singapore, in 1994, when a Great Indian Hornbill (Buceros bicornis) flew just over her head, making that sound that only hornbill wings can make. She stood in that bird’s wake, mesmerized.’

“Interesting, isn’t it? Considering that it is one of our non-native birds that had a mesmerizing effect on a visitor. The Great Indian Hornbill is a synonym for the Great Hornbill.”

The Great Hornbill, also known as the Great Indian Hornbill, is native to Sumatra, Peninsular Malaysia and northwards to the southern Himalayas.

Great Hornbills are escapees in Singapore. It was the fashion to keep such birds once and there were probably a number of smuggled birds in Singapore then. A few escaped, or were they released, for one reason or another? Anyway, from the above account, at least one bird was around as far back as 1994.

A pair of Great died in the island of Sentosa many years ago, when poison was commonly used to control the rat population there. A bird was also sighted in the Singapore Botanic Gardens, checking out a nesting hole

Currently, only a single Great Hornbill remains, causing much excitement among the urban population when it visits their homes - see here: 1, 2 and 3.

In 2006 a Great and a Rhinoceros (B. rhinoceros), both female, were seen in Eng Neo prospecting a nesting hole in an old tree - see here: 1, 2, 3 and 4.

Image of Great Hornbill at Eng Neo by YC.

February is the beginning of the breeding season and at Changi the Oriental Pied Hornbills (Anthracoceros albirostris) are busy prospecting potential nesting cavities again. This is exactly one year after two failed nesting in Changi.

Chan Yoke Meng encountered a male hornbill picking fruits of the MacArthur Palm (Ptychosperma macarthurii) (above) to subsequently place them inside a tree cavity to induce the female to enter it.

An earlier account shows a female hornbill entering the nest cavity of the Tanimbar Corella (Cacatua goffini).

One of the sites inspected by a pair is the same cavity in an angsana tree (Pterocarpus indicus) by the main road that a female sealed herself in last year. The male was seen examining the cavity as well as another nearby (left). The female was even seen entering the cavity, to emerge about five minutes later.

This time around, it would be interesting to see whether they are successful in raising chicks. If so, the population on mainland Changi would see an increase from the current two pairs.

Image of hornbill eating palm fruits by Chan Yoke Meng; hornbills at nesting hole by Allan Teo.

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“The pair of Oriental Pied Hornbills (Anthracoceros albirostris) that have been in and around Changi Village for 2-3 years now, have tried unsuccessfully to nest a few times (see Related Posts, below).

“Since last year, I have seen the pair at the main Red-breasted Parakeet (Psittacula alexandri) and Tanimbar Corella (Cacatua goffini) nesting area along the main road, on a few occasions. Each time, the cockatoos would be nowhere to be seen and the parakeets would be screaming up a storm.

“The female has tried to steal the cockatoos nest hole but no matter how hard she tried, she could not quite fit. A few times, possibly in frustration or just to stake her claim, she would place her whole body over the nest hole. As I have seen the cockatoo in that hole at other times, I could never tell if one was stuck in there during efforts.

“On January 30th, when Melanie Votaw and I visited the colony, we were surprised to find the female hornbill in the nest hole, with only her head and neck sticking out (top). We observed her for a while and Melanie managed some photos. She was rubbing her bill around the edge of the hole. The edge looked damp and brown as a result and I wondered whether she was actually using her own droppings.

“The hole still looked too small for her and was certainly much smaller and rounded compared to the normal slits that these birds choose. She would not really need to seal herself in very much, if she successfully laid eggs. The male was seen, for a short while, on a nearby branch.

“On the next Angsana tree (Pterocarpus indicus), both the Tanimbar Corella and Red-breasted Parakeet were at their own nest holes, while a Javan Myna (Acridotheres javanicus) seemed to be lining the bough of the tree as well (above). Nesting galore!

“While the population of wild Oriental Pied Hornbills at nearby Ubin is now at 22+ birds, there are limited nesting sites due to the lack of sufficient large trees and the even smaller number of suitably sized nest holes. This situation is far worse on mainland Singapore, especially away from the Central Nature Reserves.

“Nesting boxes may be the answer and this is being tried out at Pulau Ubin. If this proves successful, more boxes can be set up at Changi and other eastern nature sites, in the hope that the hornbills will successfully colonise from Ubin.”

Image of hornbill by Melanie Votaw, that of corella-parakeet by Chan Yoke Meng.