CURRENT STATUS OF BOOTED EAGLE HIERAAETUS PENNATUS IN THAILAND

Transcription

1 68 CURRENT STATUS OF BOOTED EAGLE HIERAAETUS PENNATUS IN THAILAND Chaiyan Kasorndorkbua 1/ * Chaiwat Chinuparawat 1/ ABSTRACT Booted Eagle Hieraaetus pennatus, a medium-sized eagle, is considered to be a rare passage migrant, winter visitor or even a vagrant in Thailand, according to widely-used field guides. Nation-wide raptor censuses in winter, organized by Thai Raptor Group (TRG) and volunteered by avocational birders, revealed that the species was more common than previously thought, particularly in suitable habitats. Its winter range covers four regions of Thailand, including North-west, North-east, the central plains and southern provinces. Compiled sighting records of the species in TRG database showed that its occurrence was frequent in suitable habitats, which is mainly dry ricefield, and more than five sightings per year were counted. Such records were mostly of a single bird with a particular site in Phetchaburi, at where 2 individuals were found at a sighting time, probably and partly due to abundance of prey species such as Ricefield Rat Rattus argentiventer and Roof Rat Rattus rattus. Such a site is also one of the most important wintering and roosting site for all three Aquila eagles, namely Aquila clanga, A. heliaca and A. nipalensis regularly recorded in the country. In addition, a few numbers of the species do migrate southwards over southern Thailand (south of 11 o N latitude) during autumn migration. Its passage is peaked in mid-october, according to autumn hawkwatch at Radar Hill, Prachuap Khiri Khan. Interestingly, it appeared that the dark morph of the species was more prevalent than the pale morph. The ratio of dark versus pale morph recorded within a day of the highest number at Radar Hill hawkwatch is 9 to 1. In summary, the status of Booted Eagle in Thailand may be classified as locally uncommon, rather than rare or vagrant as published in the past. Keyword: Booted Eagle, Thailand, Status INTRODUCTION Booted Eagle Hierratus pennatus is a medium-sized, eagle with feathered tarsi. Its breeding range in Asia covers the southern part of eastern Russia, northern Mongolia, north-east China and central Asia (Ferguson-Lees & Christie, 2001). The species reportedly winters in Indian subcontinent and southern Myanmar. Booted Eagle has been regarded as vagrant or rare passage migrant (Robson, 2005) or winter visitor (Lekagul & Round, 1991) in Thailand. The population found in the eastern Russia, north-east China and/or northern Mongolia likely migrate to spend winter months in South-east Asia or continue southward to Indonesian islands (McKinnon & Philips, 1993; Germi, 2005). Thailand is thus either a wintering ground or a locality on passage for the eagle. Booted Eagle has three distinct plumages, regardless of age classes, comprising dark, rufous and pale morph. The dark morph is generally dark brown whereas the pale morph is cream color on underwing coverts and underparts. The rufous morph is a lighter variant of the dark morph. In Europe where the species is locally common, pale 1/ Thai Raptor Group Faculty of Veterinary Medicine Kasetsart University, Thailand * fvetchk@ku.ac.th

2 69 morph is more frequent than dark morph (Forsman, 1999). The eagle s prey varies among habitats and reportedly includes small-sized birds, small mammals, reptiles and insects (Ferguson-Lees & Christie, 2001). Sighting records of Booted Eagle in Thailand have been scarce, less than 5 records annually. This is in part due to the plumage resemblance between dark-morphed Booted Eagle and Black Kite. The latter is a common and widespread winter visitor in Thailand hence identification difficulty arises. The study was to compile sighting records of Booted Eagle in Thailand during 3 consecutive years from June 2005 to December 2007, and to evaluate the current status of the eagle, based on the recent sighting data. MATERIALS AND METHODS Sighting records of Booted Eagle were compiled from Thai Raptor Group Database at TRG/ modules.php? name = Forums&file = br_select_table. The records are dated from June 2005 to December 2007 and are partly of the results of nation-wide raptor censuses in December and February. Information compiled included dates of sighting, number of birds observed, color morph, sighting locality and habitat type. Attempt to identify the age by plumage; juvenile versus adult was not done. Most of the records were accepted on the basis of photographic evidence, the likelihood of suitable habitat in conjunction with discussion of identification features with the observers to avoid confusion with Black Kite. Identification features presented in conventional field guides were consulted and cross-referenced (Ferguson- Lees & Christie, 2005; Robson, 2005). The records observed during migration periods e.g., April to May and September to November are regarded as on passage, especially those seen passing a watch site such as Radar Hill in Prachuap Khiri Khan whereas records dated during December and March are regarded as a winter visitor.

3 70 Figure 1. Booted Eagle, pale-morphed juvenile, Phetchaburi. Figure 2. Provinces where the sightings recorded with the number of sightings in parenthesis.

4 71 RESULTS AND DISCUSSION The compiled data are summarized in Table 1. There are 27 records of Booted Eagle. The records are scattered throughout the country covering all regions. A total of 45 birds were found in seven provinces. And that is averagely 15 sightings per year. Most sightings were of single individuals; mainly one to two birds at an observation time, except those seen on passage at Radar Hill. However, most records are more evident at two sites; Bangjak and Khao Yoi ricefield in Phetchaburi and Radar Hill in Prachuap Khiri Khan. Phetchaburi is located in the southern-most part of central Thailand. The distance between Bangjak and Khao Yoi is approximately within 15 km. Radar Hill is a raptor watch site south to Phetchaburi. The highest count of ten birds per day is on passage at Radar Hill on 22 October 2006, and was composed of nine dark and one pale morph. In all records, three morphs were observed; dark morph being the most frequently seen compared to the other two morphs. The frequency of sightings for dark, pale and rufous morph is 37, 7 and 1 respectively. The sightings were mainly found in open habitats during mid-day. There are three habitat types that Booted Eagles were found; ricefield, agricultural field and rubber plantation at Radar Hill. The ricefield was exclusively post-harvested when all rice stems were cut down, rice grains were collected and only dry fallow remained. On one occasion at Bangjak site, a dark-morphed Booted Eagle was photographed while flying and carrying a small-sized and dark brown rat in its talon. However, most of the encounters were either when the eagles were on the wings or passing through Radar Hill. Table 1. Sighting records of Booted Eagle in Thailand: 2005 to 2007 Record Date Number Morph* Locality Habitat Type No. of birds 1 13 Nov 05 1 P Bangjak, Phetchaburi Ricefield 2 25 Nov 05 1 D Bangjak, Phetchaburi Ricefield 3 26 Nov 05 1 D Bangjak, Phetchaburi Ricefield 4 6 Dec 05 1 D Bangjak, Phetchaburi Ricefield 5 24 Dec 05 1 D Trang Agricultural field 6 28 Dec 05 1 P Bangjak, Phetchaburi Ricefield 7 15 Jan 06 1 D Bangjak, Phetchaburi Ricefield 8 18 Feb 06 1 D Ban Thungsawang, Ricefield Nakhon Sawan 9 26 Feb 06 1 D Ban Nongpoentak, Agricultural field Phetchaburi 10 4 March 06 1 D Khao Yoi, Ricefield Phetchaburi April 06 1 D Khao Yoi, Ricefield Phetchaburi 12 7 Oct 06 1 D Radar Hill Passage Oct D, 1 P Radar Hill Passage Oct D, 1 P Radar Hill Passage Nov 06 3 D Bangjak, Phetchaburi Ricefield

5 72 Table 1. (con.) Record Date Number Morph* Locality Habitat Type No. of birds Dec 06 1 D Bangjak, Phetchaburi Ricefield 17 8 Jan 07 1 D Chiang Mai Agricultural field Feb 07 1 R Sri Mahabhodi, Agricultural field Prachinburi 19 4 March 07 2 D Ban Thungsawang, Ricefield Nakhon Sawan Oct 07 1 D Radar Hill Passage Oct 07 2 D & P Radar Hill Passage Oct 07 1 P Chiang Saen, Chiang Agricultural field Rai Oct 07 1 D Radar Hill Passage Oct 07 1 P Radar Hill Passage Nov 07 3 D Radar Hill Passage Nov 07 1 D Ban Thungsawang, Ricefield Nakhon Sawan Dec 07 1 D Bangjak, Phetchaburi Ricefield * P = pale morph, D = dark, R = rufous Discussion With an increase of birding coverage particularly in suitable habitats and awareness of the identification features, the sightings of Booted Eagle in Thailand is increasingly noted. The data suggest that a few birds regularly forage in certain sites throughout the winter. Thus it is not difficult to find one or two birds hunting in a suitable habitat. For those birds wintering in Thailand, they stayed between late November and March. Passage migrants are mostly found in autumn since raptor watch has been regularly done at Radar Hill for the past three years. However, sightings of spring passage is lacking due to lack of coverage during the spring migration at Radar Hill. The number of Booted Eagles spending winters in Thailand is presumed to be eight birds when repeated sightings of individuals inhabiting and foraging at a similar site i.e. Bangjak and Khao Yoi where the distance between the site is approximately within 15 km, is disregarded and a maximum number of birds per day is taken into account. The number is certainly underestimated. It appears that 24 Booted Eagles were passing central Thailand southward to the peninsula and likely migrate farther south to Malaysia and Indonesian islands where a few birds were reportedly on passage at the latter s watch site (Germi, 2005). A few Booted Eagles have been reported being on passage at Chumphon watch site (DeCandido et al., 2004). In Thailand, the data suggest that the eagle s dark morph is more prevalent than the pale or rufous morph. The finding is in accordance with observations in the eagle s breeding ground at Lake Baikal and a passage site in western Mongolia (Igor Fefelov in litt.; Axel Braunlich in litt.). This finding may reflect different breeding areas of the Asian population that winters in South-east Asia and that it is isolated from the European population. In Europe, pale morph birds are more frequent and indeed there is a trend of increasing dark morph birds from west to east (Forsman, 1999).

6 73 Sites liked Bangjak and adjacent Khao Yoi are also known to be a major foraging and roosting site for a large number of Black Kites and three Aquila eagles; Greater Spotted, Imperial and Steppe Eagles (Mallalieu, 2007; Kasorndorkbua per. obs.). Preys are plenty at the sites including two species of rats; Roof Rat Rattus rattus and Ricefield Rat Rattus argentiventer (Lekagul & McNeely, 1988) and a variety of waterbirds. An incident proves the remark for the site when a juvenile Imperial Eagle pirated a brown rat from a juvenile Greater Spotted Eagle that just forcibly stole the rat from a Black Kite (Kasorndorkbua, per. obs.). Thus it reflects a crucial role of the sites to all the eagle species to survive winters in Thailand during November and March. ACKNOWLEDGEMENTS Our thanks go to TRG members and volunteers for their assistance in raptor censuses. We are grateful to Igor Fefelov and Axel Braunlich for sharing field observation on the morph ratio of Booted Eagle. REFERENCES De Candido, R., Nualsri, C., Allen, D. and Bildstein, K Autumn 2003 raptor migration at Chumphon, Thailand: a globally significant raptor migration watch site. Forktail 20: Forsman, D The Raptors of Europe, and the Middle East: a handbook of field identification. London, U.K.: T & A D Poyser, Ltd. Germi, F Raptor migration in east Bali, Indonesia: observation from a bottleneck watch site. Forktail 21: Lekagul, B. and J. McNeely Mammals of Thailand. Bangkok, Thailand: Saha Karn Bhaet Co. Mallalieu, M Greater Spotted Eagles Aquila clanga in central Thailand. Forktail 23: McKinnon, J. & K. Philips A Field Guide to the Birds of Borneo, Sumatra, Java and Bali. Oxford, U.K.: Oxford University Press. Lakagul, B. & P.D. Round A Guide to the Birds of Thailand. Bangkok, Thailand: Saha Karn Bhaet Co., Ltd. Robson C Birds of South-East Asia. New Holland Publishers, Ltd. London. Ferguson-Lees, J., & D.A.Christie Raptors of the World. New Jersey, U.S.A.: Princeton University Press. Ferguson-Lees, J., & D.A.Christie Raptors of the World. New Jersey, U.S.A.: Princeton University Press.