The Condor 100:60!-628 0 The Cooper Ornithological Society 1998 DISTRIBUTION, RELATIVE ABUNDANCE, AND HABITAT RELATIONSHIPS OF LANDBIRDS IN THE VAVAU’ GROUP, KINGDOM OF TONGA ’ DAVID W. STEADMAN Florida Museum of Natural History, University of Florida, P.O. Box II 7800, Gainesville, FL 32611, e-mail: steadman@~mnh.uf!.edu HOLLY B. FREIFELD* Department of Geography, University of Oregon, Eugene, OR 97403 Abstract. We assessedthe distribution, relative abundance,and habitat preferences of the 12 indigenous,resident speciesof landbirdsthat survive in the Vava‘u Group, Kingdom of Tonga. We surveyed 16 islands, 10 of which are previouslyunmentioned in ornithological literature. The islands vary in land area (0.02-96 kn?), habitat composition,elevation (20- 215 m), and distance (O-lo.1 km) from the largest island of ‘Uta Vavdu. We conducted point counts along transectson 14 of the islands, and placed each count location into one of five habitat categories.Of the 11 species of landbirds that are widespread and at least locally common, 7 (Purple-cappedFruit-Dove Ptilinopus porphyraceus, Pacific Pigeon Du- cula pacijca, Common Barn-Owl Tyto alba, White-rumped Swiftlet Collocalia spodiopygia, Collared Kingfisher Halcyon chloris, Polynesian Tiiller Lalage maculosa, Polynesian Star- ling Aplonis tabuensis) certainly or probably occur on each of the 16 islands. One species (West PolynesianGround-Dove Gallicolumba stairii) is extremely rare (one small population on one island). Three speciesthat we did not record (Many-colored Fruit-Dove Ptilinopus perousii, Blue-crowned Lorikeet Vini australis, Fiji Shrikebill Clytorhynchus vitiensis) prob- ably have been extirpated from Vava‘u. The species richness and relative abundanceof landbirdson islands in Vava‘u are affected more by deforestationand other human activities than by island area, elevation, or isolation. Key words: endangered species, forest birds, island biogeography, Tonga. INTRODUCTION Ha’apai Group in 1995 and 1996. Elsewhere in The Kingdom of Tonga is part of the West Poly- West Polynesia, transect surveys of landbirds nesian avifaunal region that also comprises have been conducted in American Samoa Niue, Samoa, Wallis and Futuna, Fiji, and Ro- (Amerson et al. 1982, Engbring and Ramsey tuma (Watling 1982). The extant, indigenous 1989, Freifeld 1998) and Western Samoa (Bel- landbirds of Tonga represent 17 genera (none lingham and Davis 1988, Lovegrove et al. 1992, endemic) and 18 species (two endemic). Indi- Park et al. 1992). Another survey in Western vidual Tongan islands > 10 km2 sustain lo-13 Samoa by Evans et al. (1992) was based on speciesof landbirds today, whereas such islands sightings only and thus is less useful than sight/ each supported at least 27 species of landbirds sound surveys in quantifying relative abun- when humans arrived about 3,000 years ago dance. Mist-net surveys have been done on the (Steadman 1993, 1995, 1998). Tongan island of Late by Rinke (1991), although Based primarily upon transect surveys, we as- capture data from mist-nets may not be a reliable sess the distribution, relative abundance, and indicator of the relative abundance of birds habitat relationships of native landbirds in the (Remsen and Good 1996). Surveys such as ours Vava’u Group, Kingdom of Tonga. The only provide a first look at the incidence and abun- other published transect surveys of Tongan birds dance of landbirds in various habitats. Using are those conducted by Steadman (1998) in the similar methods on a regular basis and ideally throughout the year, these surveys are an effi- cient way to monitor bird populations among ’ ’ Received 3 November 1997. Accepted9 June habitats that differ in degree of human distur- 1998. bance. z Currentaddress: Florida Museumof NaturalHis- tory, Universityof Florida,PO. Box 117800,Gaines- Ornithological exploration of Vava’u by non- ville, PL 32611, e-mail: [email protected] Tongans began with four pencil drawings of 16091 610 DAVID W. STEADMAN AND HOLLY B. FREIFELD birds from the expedition of Alejandro Malaspi- 26.6”C, respectively, in August. Sixty-seven per- na in 1793 (Sotos Serrano 1982), currently under cent of the 2,312 mm mean annual rainfall oc- study by S. L. Olson. E. H. Layard visited ‘Uta curs from November through April. The wettest Vava‘u in the early 1870s and collected speci- months are March (364 mm, range 126-799) mens now in the British Museum (Natural His- and January (285 mm, range 50-1,009), and the tory) (Layard 1876). C. H. Townsend collected driest are June (105 mm, range 9-393) and Au- birds on ‘Uta Vava‘u on 4-5 December 1899 gust (116 mm, range 12-273). Vava’u lies near (Townsend and Wetmore 1919). The Whitney the northern limit of the South Pacific trade wind South Seas Expedition (WSSE) visited Vava’u zone, with northeast to southeastwinds prevail- in August 1925, yielding the first records of ing about 60-70% of the time, regardlessof sea- birds from several islands other than ‘Uta Va- son. va’u. No comprehensive list of species and is- The human population of Vava’u was about lands was ever published based on the WSSE 16,000 in 1993 (Christopher 1994). Archeolog- data. ical sites on ‘Eua and in the Ha‘apai Group of Studies of birds in Vava‘u since 1925 have Tonga indicate continuous human occupation for been based primarily on sight/sound records. the past 2,800-3,000 years (Burley 1994, Dick- The birds of Vava’u are treated in a general inson et al. 1994, Burley et al. 1995). One con- manner in regional books such as duPont (1976), sequenceof this human occupation is the loss of Watling (1982), and Pratt et al. (1987). In spite most indigenous species of birds (Steadman of accountsof selectedspecies on certain islands 1993, 1995, 1997a). A similar situation is likely (Gill 1988, 1990, Rinke et al. 1992), meaningful to have taken place in Vava’u, although no ar- lists of species (sensu Remsen 1994) were not cheological excavations have taken place there available before our work for any individual is- (Davidson 197 1). land in Vava‘u, nor had the relative abundances Volcanic eruptions of Late and Fonualei dur- of any species been estimated. Ten of the 16 ing the Holocene (last 10,000 years) covered the islands we visited have not been reported pre- islands of Vava‘u with tephra depositsthat have viously in the ornithological literature. weathered into rich soils suitable for cultivation of food plants. The vegetation on most islands METHODS today is thus a mosaic of mature forests (typi- cally covering only the steep land between the STUDY AREA limestone terraces), successional or disturbed The Vava’u Group is the northernmost of three forests, and active (open) or abandoned (wood- main clusters of islands in the Kingdom of Ton- ed) agricultural plantations. In the absence of ga (Fig. l), which is located east of Fiji and human influence, mature forests would be the southwest of Samoa. The volcanic islands of dominant vegetation on each island we sur- Late and Fonualei lie to the west and north and veyed. are separated from Vava’u by deep water. Va- va‘u consists of 58 raised limestone islands on HABITAT CATEGORIES a single submarine platform sloping gently to We divided the terrestrial habitats of Vava’u into the south, so that most emergent land is on the five categories:village, open plantation, wooded north side of the platform (Fig. 2). Lowered sea plantation/early successional forest, submature/ levels during the late Pleistocene glacial interval disturbed mature forest, and mature forest (Table probably united all or nearly all of these islands 2). into one island > 300 km2 in land area. By far 1. Village refers to any human habitation site. the largest island in Vava’u is ‘Uta Vava‘u (Ta- These areas are devoid or nearly so of native ble 1). Eleven other islands in Vava’u have land trees or shrubsexcept coconuts (Cocos nuciferu) areas > 1 km2, five of which we surveyed for but have scatterednon-native trees. There is no birds. regeneration of native vegetation. An irregular The only long-term climate and weather data grid of dirt roads and paths lies among the hous- for Vava’u are from ‘Uta Vava‘u (Thompson es and other buildings. Non-native vertebrates 1986), where the mean daily minimum and max- including dogs, pigs, rats, and chickens are imum temperatures range from 23.5”C and abundant. 30.2”C, respectively, in February to 2O.O”C and 2. Open Plantation refers to active agricultural LANDBIRDS OF VAVAU,‘ TONGA 611 I I I Niuafoou’ @ dTafahi v 6 ’ Niuatoputapu KINGDOM OF TONGA ~Fonualei ’ ’ Toku VAVAU’ GROUP Vavau’ Hunga @ ,%U Pangaimotu o Noa~a~u , ;\ Late Ovaka +,,“R,“,” HAAPAI’ GROUP MO’UtlQtl’One i, Haano’ DKao . >Foa 8 Tofua 1. _,JLifuka .i Uiha.0 Uoleva 20” ..‘ Nomuka FZ3lCOIl P M.WlQO~’ ‘. :-~&,“a . Hunga Hunga Haapai’ Tonga TONGATAPU GROUP wJEuaiki’ Tongatapu Eua‘ a KZllfiU ’ 22” _Ata‘ 0 20 40 R I ” t/“N f 0 20 40 $0 80 k 176 ’ 174O I I I FIGURE 1. The Kingdom of Tonga. 612 DAVID W. STEADMAN AND HOLLY B. FREIFELD Vava’u Island Group 3ELIFUKA VAKkEITU LP,NGITo O-’ $ SISIA @ AVALAU 8 ,E”AKAF*@$J -4 B TOTOKAMAKA @ EUEIKI‘ FUAAMOTU’ b 6% MUOMU’ A’ @3 0 I FANGASITO ~ONUAONE’ ONE’ Q N TAULAb Q MANINlTA 114”W FIGURE 2. Vava‘u Group, Tonga. Islands surveyed are underlined. plots. Crops in Vava‘u are usually grown be- Pandanus spp., and bananas Eumusa spp., Aus- neath an overstory of coconut trees. Most of the tralimusa spp. (sequence and nomenclature fol- cultivars are speciesintroduced or managed pre- low Kirch 1994). Modern crops also include historically in West Polynesia, such as breadfruit species introduced to Polynesia within the past Artocarpus altilis, paper mulberry Broussonetia 200 years, such as mango Mangzfera indica, cit- papyrzfera, Indian mulberry Morinda citrzfolia, rus Citrus spp., maniac Manihot esculenta, pa- kava Piper methysticum,Tahitian chestnut Zno- paya Carica papaya, pineapple Ananas como- carpusfagzfer, sweet potato Zpomoeabatatas, ti sus, and tannia taro Xanthosoma sagittifolium.