Raptor migration studies (Indonesia)

Monitoring raptor migration on Sangihe, North Sulawesi, Indonesia

The migration of raptors in the East Asian Flyway (in both Continental and Oceanic corridors) is still poorly understood, and the complex geography of the region makes studying it challenging. Only recently a handful of pilot studies highlighted how much remains to be learned.

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Observation post on the island of Sangihe

At the southern end of the flyway within the vast Indonesian Archipelago, a system of island corridors leads to the heart of the zoogeographic subregion of Wallacea, which is believed to be the main wintering ground for several species of raptors from the eastern Palearctic. However, virtually no studies on raptor migration have been carried out in Wallacea, and only a handful of records are known. Hence, in order to gather information on the magnitude of the passage, spatial and temporal distribution, and routes followed by migrants in this part of the flyway, Natural Research and Hawk Mountain Sanctuary (USA) supported a pilot study by Francesco Germi and his team on the remote Indonesian island of Sangihe. Sangihe is located along a chain of “stepping-stone” islands between Mindanao (Philippines) and Sulawesi (Indonesia), and it is likely a major concentration and passage point to the wintering areas of Wallacea. Two full-season counts were carried out in Sangihe during spring and autumn 2007, in order to determine species and numbers using this oceanic corridor.

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Flock of migrating Chinese sparrowhawks

Francesco's team study on Sangihe totaled over four months of field effort. In autumn only they recorded more than 230,000 migratory raptors of the following species:  Osprey Pandion haliaetus, Grey-faced Buzzard Butastur indicus, Chinese Sparrowhawk Accipiter soloensis, Japanese Sparrowhawk A. gularis, Harriers Circus sp., and Peregrine Falcon Falco peregrinus calidus. Chinese Sparrowhawk comprised approximately 98% of the flight, and these results and those from counts in other countries suggest that only a small percentage of this species global population overwinter west and north of Wallacea.

Francesco's team estimate that at least 400,000 raptors are streaming into Wallacea each autumn from the Continental and Oceanic Flyways combined. The raptor migration into the relatively small land area of eastern Indonesia has been unappreciated, and the count results raise a number of questions about the wintering ecology of the species concerned. Furthermore, the scarcity of winter records throughout Wallacea suggests either that observer coverage in the region is still very poor, or that a large proportion of the migrants are dispersing into remote and poorly surveyed areas possibly as far as New Guinea, or both.

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Adult female Chinese sparrowhawk

A regional meteorological analysis was carried out to establish relationships between weather and migration timing and magnitude along this section of the Oceanic Flyway. Francesco has published the study results in a peer-reviewed journal (Germi et al. 2009). A local Indonesian naturalist, Wesley Pangimangen, has been trained in raptor migration count methods, and he is now fully involved with the project. Wesley has previous work experience on the island’s endemics, in collaboration with BirdLife Indonesia Programme and the World Bank. Additional fieldwork is urgently needed to determine the wintering range of this large number of raptors, and to develop strategies for their future conservation.

This project was managed by Francesco Germi.

Photos: F. Germi

Indonesian migration paper

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Direction of migrating raptors

Francesco Germi's latest paper on the migration of raptors in Indonesia has now been published.  It looks at the Indonesian section of a major migration route recognised as the East Asian Oceanic Flyway.

Results of observations started in Bali in 2004-2005 showed major raptor migration through Indonesia; from these results it was hypothesised that other routes in the archipelago, including the Oceanic Flyway, had been overlooked. The study discovered that a huge number of Chinese sparrowhawks migrated in this area, and they accounted for up to 98% of all migrating raptors.
 
In 2007 full season raptor surveys were carried out on Sangihe Island, where a correlation between wind pattern and numbers counted at the site was discovered. More migrants were counted during crosswind conditions in spring when their route takes them along closely spaced islands than during similar conditions in autumn, when they run the risk of being blown off course during longer over-water legs of their migration. Results reveal that major and previously unrecognized raptor migration movements occur between Mindanao (Philippines) and Sulawesi (Indonesia). The chain of steppingstone islands which includes Sangihe funnels a flight of at least 250,000 raptors, comprised overwhelmingly of Chinese sparrowhawk. This indicates that the East Asian Oceanic Flyway, and not the Continental Flyway as previously thought, is the main migration route of this species in eastern Indonesia, in both spring and autumn.
 
Furthermore, examination of results from this and other studies in the region indicates that at least seven raptor species continue southeastwards into Wallacea. It is thought that a large proportion of Chinese sparrowhawks also winters in remote areas of New Guinea, leading a nomadic lifestyle following seasonal food supplies.

Francesco's work was part funded by a grant from Natural Research.
Germi, F., Young, G.S., Salim, A., Pangimangen, W. and Schellekens, M. (2009). Over-ocean raptor migration in a monsoon regime: spring and autumn 2007 on Sangihe, North Sulawesi, Indonesia. Forktail 25: 104-116.

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