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Gamauf et. al.; 1998

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http://www.www.orientalbirdclub.org/publications/forktail/14pdfs/Gamauf-Philippines.pdf 
FORKTAIL 14 (1998): 1-11
Distribution and field identification
of Philippine birds of prey:
1. Philippine Hawk Eagle (Spizaetus philippensis)
and Changeable Hawk Eagle (Spizaetus cirrhatus)
ANITA GAMAUF, MONIKA PRELEUTHNER AND WILHELM PINSKER
The two [1] forest dependent, and therefore endangered, hawk eagles of the Philippines were studied in the course of an eco-morphological raptor study carried out mostly in Luzon and Mindanao. The Philippine Hawk Eagle Spizaetus philippensis with ist two subspecies is endemic to the Philippines, whereas the Changeable Hawk Eagle Spizaetus cirrhatus (ssp. limnaetus) is widely distributed throughout South-East Asia. Both species were studied in the field, in captivity and in museum collections. The Philippine Hawk Eagle was [2] mainly found in extensive rain forests from sea level up to the mossy forest zone. In contrast, the Changeable Hawk Eagle was observed only very locally and at low elevations. Breeding records of the latter species were obtained, which provide the first breeding evidence in the Philippines. Plumage and silhouettes of both perching and flying birds are described, including the transition from juvenile to adult plumage. The major differences are in the plumage patterns, shape of the head, and form and posture of the wings. Similarities with other raptor species are pointed out in order to avoid misidentifications in the field. The adult Philippine Hawk Eagle [3] can be easily confused with the Barred Honey-buzzard Pernis celebensis because of similarities in plumage colour and pattern, and the form of wings and tail. Both hawk eagles have a [4white juvenile plumage resembling that of the juveniles of five other raptor species (Barred Honey-buzzard, Oriental Honey-buzzard P. ptilorhyncus, Rufous-bellied Eagle Hieraaetus kienerii, Philippine Serpent Eagle Spilornis holospilus, and Philippine Eagle (Pithecophaga jefferyi) and the adult plumage of the Philippine Eagle.

The two medium- s i z ed hawk e agl e s of the genus
Spizaetus are important members of the Philippine
raptor community. The Philippine Hawk Eagle Spizaetus
philippensis is listed in the world list of threatened birds
as vulnerable (Collar et al. 1994). The Vulnerable
category refers to a high risk of extinction in the wild
within the medium-term future. S. philippensis is endemic
to the Philippines and has been recorded on 11 islands,
including the main islands Luzon, Mindanao and
Palawan as well as the islands of the Visayan region
Mindoro, Leyte, Negros and Samar (Dickinson et al.
1991), and Bohol (Hornskov 1995, Sargeant 1992). In
addition, it has been observed in the past on the small
islands of Siquijor, Biliran (Visayan region) and Basilan
(Sulu Archipelago). Recent reports, however, exist only
for some of these islands: Luzon, Mindoro, Negros,
Bohol and Mindanao (e.g. Miranda 1987, Dickinson et
al. 1991, Brooks et al. 1992, 1995, Dutson et al. 1992,
Danielsen et al. 1993, Evans et al. 1993a, Hornskov
1995). The lack of recent reports on the smaller islands
may indicate that the species has either become very
rare or has completely disappeared. On Siquijor it seems
likely to be extinct: the last report stems from 1896,
documented in Rand and Rabor (1960), and the species
has not been observed in the course of recent expeditions
(Evans et al. 1993b). In some cases the respective islands
simply have not been sufficiently explored. Nevertheless,
it can be assumed that the Philippine Hawk Eagle still
Distribution and field identification
of Philippine birds of prey:
1. Philippine Hawk Eagle (Spizaetus philippensis)
and Changeable Hawk Eagle (Spizaetus cirrhatus)
ANITA GAMAUF, MONIKA PRELEUTHNER AND WILHELM PINSKER
The two forest dependent, and therefore endangered, hawk eagles of the Philippines were studied
in the course of an eco-morphological raptor study carried out mostly in Luzon and Mindanao.
The Philippine Hawk Eagle Spizaetus philippensis with ist two subspecies is endemic to the
Philippines, whereas the Changeable Hawk Eagle Spizaetus cirrhatus (ssp. limnaetus) is widely
distributed throughout South-East Asia. Both species were studied in the field, in captivity and in
museum collections. The Philippine Hawk Eagle was mainly found in extensive rain forests from
sea level up to the mossy forest zone. In contrast, the Changeable Hawk Eagle was observed only
very locally and at low elevations. Breeding records of the latter species were obtained, which
provide the first breeding evidence in the Philippines. Plumage and silhouettes of both perching
and flying birds are described, including the transition from juvenile to adult plumage. The major
differences are in the plumage patterns, shape of the head, and form and posture of the wings.
Similarities with other raptor species are pointed out in order to avoid misidentifications in the
field. The adult Philippine Hawk Eagle can be easily confused with the Barred Honey-buzzard
Pernis celebensis because of similarities in plumage colour and pattern, and the form of wings and
tail. Both hawk eagles have a white juvenile plumage resembling that of the juveniles of five other
raptor species (Barred Honey-buzzard, Oriental Honey-buzzard P. ptilorhyncus, Rufous-bellied
Eagle Hieraaetus kienerii, Philippine Serpent Eagle Spilornis holospilus, and Philippine Eagle
Pithecophaga jefferyi) and the adult plumage of the Philippine Eagle.
inhabits some other islands (e.g. Panay) or at least lived
there before the onset of intensive destruction of the
rainforests (e.g. Cebu).
The polytypic Changeable Hawk-Eagle Spizaetus
c i r r h a t u s i s , i n o u r v i e w, a l s o t h r e a t e n e d i n t h e
Philippines. The species has a vast breeding range, from
India east to South-East Asia, and south to the Sundas.
In the Philippines, the subspecies S. c. limnaetus has been
recorded in the western and southern parts of the
country, i.e. Mindoro, Lubang, Busuanga, Culion,
Palawan and Mindanao (Dickinson et al. 1991, Evans
et al. 1993a) and in Bohol (Buck et al. 1990). Dickinson
et al. (1991) recommended that Platen’s specimen from
M i n d a n a o i n t h e c o l l e c t i o n o f t h e S t a a t l i c h e s
Naturhistorisches Museum Braunschweig (Germany)
‘ should pe rhaps be r e - examined s inc e Mindanao
r epr e s ent s an out l i e r in the di s t r ibut ion pat t e r n.’
However, the species was recorded in two sites on
Mindanao during this study (see below).
The status of both species in the Philippines during
the last few decades is poorly known (McGregor 1909,
Delacour and Mayr 1946, Amadon 1953). Dickinson et
al. (1991) considered both species to be uncommon,
with S. philippensis being restricted to lowland and midmountain forests and S. cirrhatus to forested areas.
However, the Changeable Hawk Eagle had, until this
study, not been recorded as a breeding resident. Low
population density, in addition to habitat loss as a
consequence of rain forest destruction, may have
prevented ornithologists from confirming its breeding.
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