The Nias Heritage Museum maintains a small zoo with animals native to Nias for educational purposes. During a stock take of resident animals in September 2016 all but two birds could be identified. Initially the birds were thought to be either Pied Imperial Pigeons or some strain of feral pigeons. Photos of the birds were sent to some bird guides who suggested that the birds might be the critically endangered Silvery Pigeons. The photos were referred to Indonesian bird expert Bas Van Balen and Ding Li Yong who also confirmed that the two birds indeed were Silvery Pigeons. For people involved in bird conservation in Asia this was very good news. It was the first record of the Critically Endangered Silvery Pigeon on Nias Island and the only known individuals in captivity in the world.
The Silvery Wood Pigeon Columba argentina is the rarest and most imperilled pigeon species in tropical Asia. Listed as Critically Endangered by BirdLife International, it was thought to be extinct after an absence of definitive records for over 70 years until its remarkable rediscovery from both Siberut and Simeulue in the late 2000s (Lee et al. 2009; Eaton 2011) - both islands are part of a chain of island archipelagos flanking the western coast of Sumatra. Historical observations and the specimen record suggests that the Silvery Wood Pigeon was more widely distributed in Southeast Asia in the past, with scattered records from the Mentawai, Riau, Anambas, Natuna and Karimata island groups, to the coastal islands (e.g. Burong) off southwest Sarawak, Malaysian Borneo.
Historical accounts on the ecology of the Silvery Wood Pigeon indicates that the species disperses widely among small islands in Sundaic Southeast Asia to forage for fruits. There is also evidence to suggest that it associate closely with the unrelated, but similar-looking Pied Imperial Pigeon Ducula bicolor, a common small-island and coastal forest specialist widely distributed across Southeast Asia. This surprisingly level of similarly in plumage patterns may have led to confusion in the identification of the two pigeon species in the past. The reported association with Pied Imperial Pigeons is also consistent with recent observations in Siberut that led to its rediscovery in 2007-2008 where an individual was seen in flight over coastal forest in southern Siberut with small groups of Pied Imperial Pigeons. In 2011, individuals observed for the first time at Tanahbala in the Batu Islands were also associated with Pied and Green Imperial Pigeons.
Background information of Silvery Wood Pigeon record
A pair of Silvery Wood Pigeons were trapped from the hilly lowland forests near La’usȍ village, Ono Hazumba sub-district, Nias Selatan (South Nias) regency in June 2016. La’usȍ is located in western Nias and is about nine kilometres inland from Nias’ Indian Ocean coast. Like much of the interior of Nias, this area is hilly and mostly covered in dense secondary forest. While this part of Nias is relatively inaccessible, there are major rural settlements in the area and there are no remaining areas of truly virgin rainforest on the island. A large part of the vegetation in this area is considered as ‘kebun’, which contains mostly planted crops and fruit trees such as rubber, cacao and the pinang palm. Natural forest remnants occur in deep gorges or on steep ridges, but these areas are also regularly visited by villagers collecting food or wood.
The trapper that obtained the pigeons noted that June is a good time to hunt pigeons, and that many of them lived high up in the tree canopy. Using a large mist net, he caught a number of birds, among them two Silvery Wood Pigeons. According to the trapper, the pigeons were not as valuable as songbirds which can be sold to bird traders (e.g. Nias Hill Myna and White-rumped Shama), but were kept as decoys to capture other birds. After a few weeks use as decoy, the pair of pigeons were passed on to another family in the village, who happened to be related to one of the zookeepers at the Nias Heritage Museum. On 6 August 2016, the family eventually passed the birds to the museum where they were provisionally held. As the identity of the pigeons was initially uncertain, photographs were taken and sent to various Indonesian bird experts for identification.
New aviary being built for the Silvery Pigeons.
Soon after the birds were identified a group of international experts started advising the Museum on the how to care for the birds. Initially the option of releasing them was discussed, but some experts said that they could have contracted diseases in captivity that could be spread amongst the wild population. The birds were moved to a large cage and their diet was improved. A customized Silvery Pigeon aviary (4 x 6 meters, 3 meters high) was built at the Museum, funded by Heidelberg Zoo in Germany. Once the birds have settled there the next step would be to determine the sex of them, and if possible start a controlled breeding program at the Museum.
Discussion
The record described here represents the first documentation of the Silvery Wood Pigeon on Nias Island. We are not aware of historical or recent records of the species on the island. Our record here also suggests that the Silvery Wood Pigeon is widespread across the island archipelagos off west Sumatra, since there is now recent records from four major island clusters (i.e. north: Simeulue, central: Nias, Batu, south: Siberut) and it is highly likely that the species will show up in the Pagai group. Future surveys should aim to determine the population sizes of the pigeons in each of these islands but given the extent of forest remaining, it is possible that the current population size (c. 50 mature individuals) is grossly underestimated. Similar surveys should also be extended to other former range islands in the South China (e.g. Bungaran) and Java (e.g. Gurungan) seas where significant forest cover remains.
Björn Svensson and zoo keeper Ama Yuanita at the inauguration of the new purpose built aviary.
It is unclear to what extent is the Silvery Wood Pigeon threatened by illegal trapping activities. An undocumented record of a pair in a private collection in Hong Kong indicates that the species is sought by collectors, but remains the only evidence of the species in the aviculture industry. We are unaware of any collections or breeding programmes of the pigeon in zoological institutions around the world. Although the songbird trade in Indonesia is mostly driven by species with attractive vocalisations and plumages, there is also a growing demand for rare and valuable species is may threaten the Silvery Wood Pigeon among other declining species like the Bali Starling and Javan Hawk Eagle. Bird hunting on Nias is widespread and the main motivation of most trappers is to catch songbirds for sale, and so like this record, the Silvery Wood Pigeon may be incidentally trapped by poachers aiming to obtain other high value species. We recommend more survey efforts in Nias to monitor these trapping activities as it may lead to further decline of many common forest birds, and have already led to the extirpation of the endemic Nias Hill Myna from most parts of the island.
Many thanks to Bas van Balen, Colin R. Trainor and Panji Gusti Akbar for correctly identifying the birds. Thanks also to Dr Ian Singleton and Simon Bruslund for advice on aviary design and caring for the birds.
This blog post is based on the article “A first record of the Critically Endangered Silvery Pigeon (Columba argentina) on Nias Island, Indonesia” by Björn Svensson & Ding Li Yong, that appeared in Birding Asia 26 (2016): p 73-75.