PARTNERS: Hornbills generally mate for life. — Photo by Ch’ien C Lee
INTERNATIONALLY recognised hornbill expert Dr Pilai Poonswad was in Kuching last month for the Sarawak Bird Race 2011. I was fortunate to have the opportunity to discuss this iconic bird with her.
COOPERATIVE SPECIES: The white-crowned hornbill. — Photo by Cynthia Lobato
To say that Poonswad is passionate about studying and conserving hornbills is a grand understatement. She has trekked and camped in the forests of Thailand, in particular Khao Yai National Park, during her quest. In 1993, she established the Hornbill Research Foundation and in 2006, she won the Chevron and Rolex Awards for her work with these majestic indicator birds.
Sarawak is often referred to as ‘The Land of the Hornbills’ despite hosting only eight of the 45 species. Members of the Buceratidae family spread from Africa to Asia and the South Pacific. Thailand has 13 species, which includes the eight found in Sarawak – white-crowned hornbill (Aceros comatus), bushy-crested hornbills (Anorrhinus galeritus), wreathed hornbill (Rhyticeros undulatus), wrinkled hornbill (Aceros corrugatus), rhinoceros hornbill (Buceros rhinoceros), helmeted hornbill (Buceros vigil), oriental pied hornbill (Anthrococeros albirostris), and Asian black hornbill (Authracoceros malayanus).
Poonswad explained that she used GPS to track hornbills, discovering that their range at 600 sq km was substantially larger than what was found with the radio tracking.
These trophy species, which are high on bird-watchers must see list, are also indicators of forest health. If the forest is healthy with fruit and nest trees, there are likely to be hornbills, but if the structure of the forest has been damaged through, for example logging or hunting, hornbills are likely not to be present.
She pointed out that hornbills, major consumers and dispersers of seeds, are ecologically very important in distributing seeds. Food, shelter (protection from the weather and predators) are a necessity, but often the presence of the specialised hornbill nesting sites – hollows in living trees – are forgotten and these must be available if bird populations are to stabilise and grow.
Hornbills, which generally mate for life, do not dig their own nesting holes, instead these must be in naturally forming holes in living trees (that could be created by fungi or woodpeckers for example) at 20 to 30 metres above the ground. The female, which lays two to five eggs, is sealed in for protection from predators. Her mate feeds her, except in the two species, bushy-crested and white-crowned, which are co-operative species and the flock cares for nesting females. If the male in the other species dies, so do the female and the chicks.
Poonswad said in lowland tropical forests in Southern Thailand, the preferred nesting tree was a member of the Dipterocarp family – Dipterocarpaceae.
She added that the holes in trees which hornbills nest in must meet very specific requirements and are often the limiting factor for successful reproduction of hornbill pairs. Poonswad chuckled over the times she has seen the females scolding her mate, making comparisons to humans.
The naturally forming holes are often used for several years, however, if nests are abandoned, her team will determine the cause. Sometimes the hole has become too deep, thus the remedy is simple – fill it up. At present soil is used, but she is experimenting with longer-lasting materials.
Sometimes the entrance to the hole is too big for the pair to block and then the solution is to make it smaller. In addition, larger dominant species of hornbills, such as the rhinoceros and the great will chase away smaller species.
Nesting trees have also been removed so Poonswad creates the hollows. When she described placing nest boxes in the forest for the hornbills, I saw in my mind boxes with holes on poles. This is not the case. As hornbills nest in live trees, the artificial nests must be attached to the preferred species and at the preferred heights and her research assistants climb the trees to attach the nest boxes at the preferred levels.
Most hornbills, with the exception of the helmeted, are able to perch on the edge of the hole, but due to the weight of its casque, the hole must be beside a branch. She designed a box especially for this species, but with a crash of its casque, the box was demolished. The box could not withstand the test given by the helmeted hornbill – it did not meet the strength requirements.
As Poonswad spoke, I reflected on the complexity and interconnectedness of the world. The existence of hornbills and the forests are intertwined in a complexity that one is unlikely to survive without the other; hornbills disperse seeds but also need large trees to nest in. Without food, the decline is quick, but without nesting sites, the populations dwindle.
To learn more about hornbills read the ‘Phillipps’ Field Guide to the Birds of Borneo’ by Quentin Phillipps and Karen Phillipps.