The Nest, Eggs, and Diet of the Papuan Harrier from Eastern New Guinea

J. Raptor Res. 44(1):12–18 E 2010 The Raptor Research Foundation, Inc. THE NEST, EGGS, AND DIET OF THE PAPUAN HARRIER FROM EASTERN NEW GUINEA ROBERT E. SIMMONS1 DST/NRF Centre of Excellence, FitzPatrick Institute, University of Cape Town, Rondebosch 7701, South Africa ABSTRACT.—The Papuan Harrier (Circus spilonotus spilothorax), currently classified as a subspecies of the Eastern Marsh-Harrier (C. spilonotus), is endemic to the island of New Guinea and may be in need of conservation attention because of threats from grassland burning. I here detail the discovery of the first known nests in lowland Papua New Guinea and provide egg dimensions and prey data. Both nests were initiated in early April, in damp rank grassland, and contained three small chicks in mid-May. The only egg measurements, combined with one previously published record, suggest large egg volume and concomitant large female body size (estimated to be ca. 890 g). At this size, this may be the world’s largest harrier. Fire destroyed both nests within 5 wk of their discovery. An atypically slow foraging style and a preponderance of game birds and large rats (Rattus spp.) in the pellets and prey remains are consistent with large body size. Further studies of the bird’s ecology and breeding are needed for a comprehensive understanding of its conservation status and threats to its population. KEY WORDS: Papuan Harrier; Circus spilonotus spilothorax; Eastern Marsh-Harrier; Circus spilonotus; body size; diet; egg size; foraging; Papua New Guinea. NIDO, HUEVOS Y DIETA DE CIRCUS SPILONOTUS SPILOTHORAX DEL ESTE DE NUEVA GUINEA RESUMEN.—Circus spilonotus spilothorax, actualmente clasificada como una subespecie de C. spilonotus,es ende´mica de la isla de Nueva Guinea y puede necesitar medidas de conservacioń debido a amenazas provenientes de la quema de pastizales. Aquı´ detallo el descubrimiento de los primeros nidos encontrados en las tierras bajas de Papuá Nueva Guinea y brindo las dimensiones de los huevos y datos de las presas. Ambos nidos fueron iniciados a principios de abril en pastizales hu´medos y albergaron tres pequenõs pichones a mediados de mayo. Las uńicas medidas de los huevos realizadas en este estudio, combinadas con un registro publicado anteriormente, sugieren un volumen grande del huevo y un tamanõ concomi- tantemente grande del cuerpo de la hembra (estimado en ca. 890 g). Seguń este tamanõ, podrıá ser el gavilań ma´s grande del mundo. El fuego destruyo´ ambos nidos dentro de las cinco semanas de su descubrimiento. Un estilo de forrajeo atı´picamente lento y una preponderancia de aves de presa y ratas (Rattus spp.) de gran tamanõ en las egagro´pilas y en los restos de presas son consistentes con un tamanõ de cuerpo grande. Se necesitan ma´s estudios sobre la ecologıá y la reproduccioń de esta especie para alcanzar un conocimiento amplio de su estado de conservacioń y de las amenazas a su poblacioń. [Traduccioń del equipo editorial] Avifaunal studies on the island of New Guinea of breeding seasons, conservation issues, and behav- began with numerous ornithological expeditions ioral ecology of other New Guinea birds have (e.g., Rand 1942, Mayr and Gilliard 1954, Gilliard emerged (Bell 1982a, 1982b, Dumbacher et al. and Lecroy 1961, 1967, Hoogerwerf 1964, Diamond 1992, Symes and Marsden 2005, Marsden et al. 1972) but have focused primarily on the colorful 2006) including that of the poorly known endemic Birds of Paradise (Paradisaeidae: Mack and Wright raptors (Legra 2005). A bird almost entirely over- 1996, Frith and Beehler 1998). With the exception looked in this increased research activity is the Pap- of studies by Diamond (1985) and Heads (2002), uan Harrier (Circus spilonotus spilothorax). I here this has often been at the exclusion of other endem- present data on the breeding and diet of the Papu- ic fauna. However, in the last three decades, studies an Harrier, an endemic raptor species for which occasional sightings, a single egg record, and pho- tographic records of captive birds represent most of 1 Email address: [email protected] our knowledge (Coates 1985, Coates and Peckover 12 MARCH 2010 NESTS AND DIET OF PAPUAN HARRIERS 13 2001). Moreover, this birds’ species status is also bird (if known). I simultaneously recorded the hab- controversial, with several authorities believing it itat over which they foraged and the number of prey to be a subspecies of the Western Marsh-Harrier strikes in relation to successful captures. The bird’s (Circus aeruginosus) or Eastern Marsh-Harrier (C. subsequent behavior was followed using 8.5 3 42 spilonotus; Brown and Amadon 1989, Ferguson-Lees binoculars. Food-carrying male harriers typically and Christie 2001, BirdLife International 2004). pass their prey to a dependent female or young in Other authors, perhaps more familiar with it in an aerial food pass (Hamerstrom 1986, Simmons the field, have recommended full species status 2000) and in this way I found both sites following based on its endemic residence status, plumage dif- each female’s return to her nest. ferences, and the fact that Eastern Marsh-Harriers I visited the two nests on two occasions: (1) to do not visit the island of New Guinea (Simmons record the eggs or young upon first finding the 2000, Coates and Peckover 2001, I. Fefelov pers. nest, and (2) to note progress, take blood samples, comm., J.-M. Thiollay pers. comm.). and to measure eggs and chicks using Vernier calli- During an expedition to the island in 2007, I sur- pers. A third visit was made by independent observ- veyed sites likely to hold harriers and undertook ers to record nest success or failure. During nest road counts and area assessments to determine visits, I collected any pellets regurgitated in the nest the first population estimate and threats to this spe- and also searched the area below favored perch sites cies (Simmons and Legra 2009). I here describe (especially isolated trees) for pellets. At both nests, I details of the habitat and dimensions of the two assessed prey remains in chick crops by gently push- nests, and provide the first description and photo- ing remains into the gape and removing them for graphs of the eggs and chicks, as well as notes on examination and photography. All regurgitated the diet and hunting of this poorly known endemic contents were then re-fed to the chicks. Photo- raptor. Other details may be found in Simmons and graphed mammal material was identified by K. Legra (2009). Aplin of the Commonwealth for Scientific and In- dustrial Research Organization, Australia, and bird STUDY AREA AND METHODS material by B. Beehler of the Smithsonian Institute, Surveys for this species in Papua New Guinea Washington, DC U.S.A. (PNG) were undertaken in April–May 2007 to look for breeding birds in the eastern highlands cen- RESULTS tered on Goroka (6u059S, 145u259E) and the north- Discovery and Dimensions of First Nests. No eastern lowlands of the Ramu and Markham valleys nests were found in the highlands around Goroka, (5u57.0459S, 145u54.3309E). I searched for breeding but two nests were found in lowland Papua New birds in areas where most sightings had been report- Guinea (Table 1). Both were in damp areas, domi- ed previously (Coates 1985, pers. comm.) and more nated by tall rank grass and entirely shaded from recently from biologists and birding tour operators the sun by overhanging vegetation, and invisible (e.g., B. Beehler, P. Gregory, R. Heinsohn, and R. to the observer from .2 m. Both nests were found James pers. comm.). Road surveys comprised two following food transfers from male to female. observers travelling at variable speeds up to 80 km/ One nest contained two small downy nestlings hr and recording all raptors seen per km in lowland and one unhatched egg (Fig. 1, 13 May 2007), and highlands. Area-specific searches were carried which later hatched, making three nestlings total; out at three localities (1) Mt. Hagen, particularly the second nest had three small downy nestlings the protected airfield (5u469S, 144u179E; 1800– when first found on 15 May 2007. The only egg 2800 m asl), (2) Goroka, including the airfield found in Nest 1 was a typical dirty-white harrier and surrounding grasslands (1500 m asl), and (3) egg with large dimensions of 49.18 mm in length a 50-km stretch of lowland valley in the Ramu and and 43.17 mm in width. Both nests showed asyn- Markham valleys centered on Waterais (5u579S, chronous hatching, with the two older nestlings sim- 145u549E; 400–500 m asl). ilar in size and development, and a third apparently To locate nests, I observed the foraging behavior 3–4 d younger. In Nest 2, the youngest nestling of focal birds from a slowly moving vehicle or an appeared subordinate, with some down missing elevated area, until a prey-strike was observed. I re- around its crown, suggesting sibling aggression. corded the target species, the outcome of the forag- Food was always found in the nests during four ing attempt, and the sex and age of the foraging (mid-morning) visits and the crops of nestlings were 14 SIMMONS VOL. 44, NO.1 Table 1. Nest dimensions and contents of two Papuan Harrier nests from the Ramu and Markham valleys, Papua New Guinea, May 2007. DATE ESTIMATED FIRST NEST LOCATION [ALTITUDE] FOUND EGG DATE1 CONTENTS NEST AND VEGETATION DETAILS No.1 Markham 6u09.7159S, 13 May 6 April 07 1 egg, 2 small 1.0-m-high reeds shading nest; nest Valley 146u08.4949E downy nestlings 50 3 50 cm, 25 cm deep; on damp [404 m asl] ground; made of dry grass; well concealed in grassland No.2 Ramu 5u57.0459S, 15 May 2 April 07 3 small downy 1.2-m-high reeds shading nest; nest (Gusap) Valley 145u54.3309E.

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