| Hornbills |
Hornbills are a charismatic group of tropical birds characterized by their long decurved bills, sometimes with a casque on the upper mandible.
The Visayan Tarictic Hornbill (Penelopides panini) and the Walden’s Hornbill (Rhabdotorrinus waldeni, local name: “Dulungan”) are two threatened hornbill species endemic to the islands of the Western Visayas, which means that they only exist in this region.
These birds are primarily frugivores. By distributing seeds with their droppings, they function as seed dispersers and thus play an important role in the local ecosystem. For example, they are vital for the survival of large fruit-tree species which are dependent on “their” dispersers. Furthermore, seed dispersers generally aid in reforestation.
Hornbills show very interesting breeding behaviour: Before incubation, they begin to close the entrance of the nest cavity with natural materials such as mud and fruit pulp. After the female has entered the cavity to lay her eggs, the entrance is closed even further. Only a hole small enough for the male to feed the female and her offspring remains. This behavior helps to protect the nest from rival hornbills and predators. Once the chicks have grown, the barrier in front of the nesting site is destroyed.
Nowadays, the Visayan Tarictic Hornbill and the Walden’s Hornbill are both considered critically endangered species. Several factors have contributed to this development: First, deforestation and illegal logging has led to a rapid decrease of their population, as hornbills mostly nest in natural cavities in trees. Furthermore, the poaching of nests for the pet marked has played a role in these species becoming critically endangered. Because of their slow reproduction, it is hard for them to recover their population under these circumstances.
The Visayan Tarictic Hornbill and the Walden’s Hornbill have already been rendered extinct on several Philippine islands. The Tarictic is extinct on Ticao, Guimaras, and all the small islands, virtually extinct on Masbate, and critically endangered on Negros. Historically, the Dulungan only occurred on Negros, Guimaras and Panay. Today, it is extinct on Guimaras and virtually extinct on Negros. Thus, the last resorts of the Visayan hornbills are the forest remnants of Panay.
PhilinCon aims to protect these and other threatened species, for instance through nest guarding, installation of nest boxes, and rehabilitation of injured animals. Thanks to our work, the number of hornbills on Panay has increased significantly in the recent years. Still, these rare and vulnerable species require our attention and protection, in order to save these iconic and unique Visayan birds from extinction.
| what important role play the Hornbills? |
Importance of seed dispersers like hornbills for the forest
While eating fruits, a lot of them fall on the ground. This is great for ground-dwelling species like other birds, mammals or arthropods. The direct fruit dropping is not the only great thing that helps the other organisms.
Seed-dispersing species such as hornbills and fruit bats feed on fruits of endemic plants and distribute the seeds with their droppings. Today, the Visayan Warty Pig is the most important seed disperser for very large fruits. In ancient times, some of the now extinct megafauna (elephants, rhinos, etc.) have played a crucial role in dispersing large fruits. Intestinal passage and the dispersal facilitate the germination of certain seeds. The chemical composition of the fruit affects the duration of the gut passage. This way, the plant can manipulate dispersers to achieve dropping of seeds in an optimum average distance from the tree, in places where they germinate best. This is because survival is reduced directly under the tree due to accumulation of natural enemies under the mother tree – tree whose seeds are used for propagation -, which harm the seedlings.
Seed-dispersing species are ecologically important helpers in rainforest regeneration and reforestation and therefore need to be protected. Large-fruited tree species may vanish if they lose “their” disperser species which they co-evolved with. PhilinCon protects such frugivorous animal species.
Janzen, D. H. & P. S. Martin (1982): Neotropical anachronisms: the fruits the gomphotheres ate. Science 215: 19-27.
Mangan, S. A., Schnitzer, S. A., Herre, E. A., Mack, K. M. L., Valencia, M. C., Sanchez, E. I. & J. D. Bever (2010): Negative plant–soil feedback predicts tree-species relative abundance in a tropical forest. Nature 466: 752-755. [PDF]
Protection of hornbills and their nests in the wild
In order to diminish losses caused by poaching and to increase the population size of seed dispersers, a variety of measures like anti-poaching measures (“rice for rifles”) and alternative livelihood programs have proven to be efficient.
Found hornbills are treated by veterinarian Dr. Sanchez in our rescue facility. Young birds are reared there until they are fully grown. After rehabilitation and a final health check, the birds are released back into the wild. Surveillance of nests of the large and particularly threatened Dulungan (Rhabdotorrhinus waldeni) by paid work through locals has proven to be extremely successful. The losses from poaching (brood and sometimes also females killed) dropped from previously 50% to 5% since 2001.
Due to recent unjustified criticism, we would like to point out that the goal of any conservation measure is the survival of the species, particularly when they are considered critically endangered. Nevertheless, the nest guarding program provides an environmentally sustainable income for local people and has increased the number of breeding pairs.
Enhancing the breeding success of endangered hornbills
Experience has shown that, with too many old rainforest trees having been logged, the remaining breeding pairs are competing for nest holes. Therefore, artificial hornbill nest boxes were developed and attached to the trees. To slow rotting, the rather heavy nest boxes are made out of mahogany, a hardwood timber not native to the Philippines. By using wood of this locally grown alien tree species, regeneration of native hardwood tree species is indirectly supported.
One of the two hornbill species at stake has already nested several times in boxes thus hung up by PhilinCon.
Successful hornbill releaseS (1998 - 2005 - more birds have been released in the meantime)
A Visayan Tarictic male (Penelopides panini), confiscated as a fledgling and reared and trained by PhilinCon staff, was gradually subjected to a ‘soft release’. It bonded with a wild flock, while becoming more and more independent of offered food. This was the first of any hornbill releases. Until early 2005, 22 Tarictic Hornbills could be successfully released, all of which had been equipped with transmitters so the success could be monitored. More Tarictics have been released since then. The experience from these releases helped to prepare the release of rehabilitated birds of an even more threatened species, the Writhed-billed Hornbill or Dulungan. Three Dulungans, one male and two females, were released in the Northwest Panay Peninsula Natural Park in April 2015. Meanwhile, not only survival of most of the released hornbills but also successful breeding of Tarictics with wild mates can be reported. Furthermore, pair formation of released birds in the wild occurred soon upon release. Nest boxes were offered by PhilinCon in the forests around the station, and are accepted by wild Tarictics for breeding since 2002.
The rehabilitation and release program was sponsored by Frankfurt Zoological Society, IDEXX, Chester Zoo, and the Mohamed Bin Zayed Species Conservation Fund, and still is by the Association for Bird Conservation and Aviculture (AZ) and the Bird Protection Committee.
Taken from: E. Curio (1998): The first ‘soft release’ of a juvenile Tarictic Hornbill (Penelopides panini panini). Publication No. 19 of the Philippine Endemic Species Conservation Project (PESCP) of the Frankfurt Zoological Society. Report compiled from records of Fel C. Cadiz, Benjamin ‘June’ Tacud, Henry Urbina and Eberhard Curio.
Lichtblicke für die Natur (2003): Newsletter, Stiftung bedrohte Tierwelt (Foundation for Endangered Wildlife). Frankfurt Zoological Society (German, authored by E. Curio: Highlights of Progress for Nature).
Recommended literature: Margoluis, R., Salafsky, N. & Balla, A. (Illustrator), 1998: Measures of success: Designing, managing, and monitoring conservation and development projects. Island Press. ISBN: 1559636122 (Paperback, 363 pages)
Where is the difference between Walden´s & Writhed Hornbill?
Walden’s Hornbill (Rhabdotorrhinus waldeni) vs. Writhed Hornbill (Rhabdotorrhinus leucocephalus)
Walden’s Hornbill, Rhabdotorrhinus waldeni of Panay and Negros, was thought to be con-specific with Writhed Hornbill, Rhabdotorrhinus leucocephalus of Mindanao.
Walden’s Hornbill Writhed Hornbill
Walden’s was split because it differs in the terms of:
- the colour of the bare parts/gular pouch, yellow and blue in Walden’s, red in Writhed
- the degree of sexual dimorphism, greater in Walden’s
- the plumage, Walden’s having an entirely rufous head and neck.
IUCN calls Walden’s Hornbill Rufous-Headed Hornbill, to distinguish it from Rufous Hornbill, elsewhere in the Philippines.