Notornis, 2003, Vol. 50: 75-82 0029-4470 O The Ornithological Society of New Zealand, Inc. 2003 Breeding biology of bellbirds (Anthornis melanura) on Tiritiri Matangi Island SANDRA H. ANDERSON School of Geography and Environmental Sciences, University of Auckland, Private Bag 92019, Auckland [email protected] JOHN L. CRAIG School of Geography and Environmental Sciences, University of Auckland, Private Bag 92019, Auckland Abstract Bellbird breeding activity was monitored on Tiritiri Matangi Is in 1977 and 1978. The density of bellbirds breeding within the study area was 2.13 pairs ha-'. Resighting of banded adult birds in consecutive years was 69% and less than half the pair bonds were maintained into the following season. Breeding extended from Oct to Jan, with a peak in Nov. Most nests were built in tree ferns, and the mean clutch size was 3.6 eggs. Incubation and nestling periods were c. 12 and 14 days, respectively. The female bellbird was significantly more active than the male in care of the nestlings. Measurements of chick head and wing length were correlated with age. Nest success was 44%, and daily survival rate 97%. Predation, desertion, and exposure contributed to nest failure, and re-nesting was common. The mean number of nests female-' season-' was 1.3, while mean reproductive success was 2 chicks fledged. Young were independent 2 weeks after fledging, and moulted to adult plumage in their 1st year. The dynamics of the Tiritiri Matangi population, when compared with other populations, suggest that breeding behaviour is a flexible response to environ- mental factors, and will vary between populations depending on the level of predation, competition and habitat quality. Anderson, S.H.; Craig, J.L. 2003. Breeding biology of bellbirds (Anthornis melanura) on Tiritiri Matangi Island. Notornis SO(2): 75-82. Keywords bellbird; Anthornis melanura; breeding biology; reproductive success; population dynamics; Tiritiri Matangi Island INTRODUCTION the potential for successful future management of The bellbird (Anthornis melanura) is a small the species. The study characterises the breeding honeyeater (Meliphagidae) endemic to the islands of behaviour of bellbird on Tiritiri Matangi and New Zealand. Bellbirds formerly occurred through- identifies trends in the timing and duration of out New Zealand, including most offshore islands each breeding stage. Aspects of the population from the Three Kings Islands (31%) to the Auckland dynamics are compared with those of bellbirds on Islands (5405), but are now rare north of 3805. All other offshore islands and the mainland of New New Zealand honeyeaters suffered a decline in the Zealand. The role of predators, competitors, and north during the 1860s (Buller 1873; Turbott 1961; habitat quality in the dynamics of bellbird Craig & Douglas 1984). The stitchbird (Notiomystis populations is discussed. The proposal that cincta), which is the most subordinate of the 3 bellbirds on the Poor Knights be classified as a species (Craig et al. 1981b; Craig 1984), was reduced distinct subspecies from bellbirds in the North to a single population on an offshore island. Island (Bartle & Sagar 1987) is also examined. Whereas the largest and most dominant of the 3 species, the tui Prosthemadera novaeseelandiae (Craig METHODS AND STUDY SITE et al. 1981a)has returned to all areas except the Three Study area Kings Is, bellbirds have not re-established in the Bellbirds were studied on Tiritiri Matangi Island, northern mainland. Reasons for the decline are situated in the Hauraki Gulf 25 km north of uncertain, and although a number of attempts have Auckland, New Zealand. At the time of study, the been made to re-establish bellbird into northern bellbird population was c. 150 and much of the forests all transfers have been largely unsuccessful. island's 220 ha was rough pasture, with pockets of In contrast, on even northerly offshore islands, the remnant forest totalling <20 ha. The study bellbird is common and in the absence of introduced was conducted primarily in the largest (4 ha) forest mammalian predators attains high densities relative patch, shortly after grazing had ceased and to the mainland (Bartle & Sagar 1987). the island vegetation had been left to regenerate. The aim of this paper is to expand the baseline The study forest comprised mixed coastal information on bellbird ecology, thereby increasing species, with a canopy including kohekohe (Dysoxylum spectabile), taraire (Beilschmiedia farairi), Received 30 March 2002; 29 August 2002 mahoe (Melicytus ramiflorus), and pohutukawa 76 Anderson & Craig (Metrosideros excelsa). Individual rewarewa estimate and confidence intervals for nest success (Knightia excelsa) and a single puriri (Vitex lucens) of bellbirds on Tiritiri Matangi. To obtain an were important nectar sources. The shrubs indication of population dynamics, the number of Coprosma rhamnoides, C. areolata, and Geniostoma breeding attempts and productivity female-' were ligustrifolium provided a late season fruit source also calculated. Factors contributing to nest failure within the study forest. Bellbird activity in the were identified where possible. coastal and valley areas adjacent to the study forest was also observed. The vegetation of these areas Parental role was dominated by New Zealand flax (Phormium Active nests were observed routinely at a discrete tenax), ti (Cordyline australis), kanuka (Kunzea distance for 1-h periods, to compare activity ericoides), manuka (Leptospermum scoparium), between progressive breeding stages and determine and pohutukawa. the relative role of each parent. The parent was identified at each visit to the nest, and where Distribution possible food items brought to the nest were also The 4 ha study forest was gridded at 15 m identified. The duration of visits to the nest, and time intervals. Adult birds using the study area had intervals between visits, were recorded using a previously been captured in mistnets and individual- stopwatch. Where duration exceeded the 60-min ly colour-banded. Individuals were identified on observation period, the minimum time was sighting and their position plotted to provide an recorded. Eleven nests from 9 pairs were monitored estimate of the range and core area of bellbird pairs. for a total of 140 h over the course of the study. Nest localities were mapped to calculate the density of breeding pairs within the study area. Survivorship RESULTS of individuals, as well as maintenance of pair bonds Distribution into the following season, was monitored. The average range of a bellbird pair was 201m2 (SET = 28, n = 9) centred on the nest. Exclusiveness Breeding of the core area, and size, varied between pairs Bellbird breeding activity was intensively (K = 139 m2, SET = 22, n = 9). During the breeding monitored in Oct-Jan for 2 seasons (1977 and 1978), season, both members of the pair were typically with additional observations made in the found within the core area throughout the day. The preceding 4 years. Information was obtained for 27 range of most pairs overlapped at flowering nests from 17 pairs. Nests were found by observing resources temporarily in demand by other paired birds for signs of breeding activity. These bellbirds. At times when no substantial nectar included carrying nesting material or food, hurried source occurred within the core area, the male feeding and 'twittering' behaviour by the female, defended feeding access within these areas of and worn tail feathers, brood patches, and extrud- resource overlap.-important plant species during ed cloaca in brooding females. Recorded song was the breeding season were flowering flax, rewarewa also used to lure females, and the responding bird and pohutukawa. Kanuka, manuka, ti, mahoe, could then be followed back to a nest. Nests were hangehange, ngaio (Myoporum laetum), mapou described, and where possible monitored daily to (Myrsine australis), and the native jasmine assess building and laying activity. Clutch size and (Parsonsia heterophylla) provided alternative lower the hatching success of eggs were checked while reward nectar resources (Craig 1986; Anderson the parents were absent from the nest, using a 1997; Castro & Robertson 1997). ladder and nest mirror. Head, wing, and tarsus Observations of territorial pairs and nests measurements of the nestlings from a single nest revealed 8 breeding pairs within the 4 ha study were taken daily using vernier calipers to obtain area in Nov 1977 and 9 in Nov 1978 (mean a growth pattern. Nestlings were fitted with density 2.13 pairs ha-1). Numerous single birds also individual colour band combinations before fledg- regularly used or resided in the same area, ing. Fledglings were monitored to independence, resulting in a higher density of individual birds. and the fate of juveniles recorded where possible. Tui held breeding territories in the study area at a similar density and competed for the same nectar Reproductive success resources (Stewart 1980). Dominance over the core To allow some comparison with the Poor Knights area decreased after fledglings were independent population, survival was calculated in the same and nesting had ceased. Although each pair manner as Sagar (1985). To obtain a true measure remained largely site-attached throughout the of nest success, while accounting for bias because year, they spent varying amounts of time away of incomplete breeding records, Stanley's (2000) ' from the core area depending on food availability. method was used to estimate stage-specific daily All but one of the 16 paired adults on Tiritiri survival probabilities, and to calculate a point Matangi in 1977 were banded, and of these 11 were Bellbird breeding on Tiritiri Matangi 77 resighted the following year. Although the fate of the unbanded bird could not be certain, it was not observed with its banded mate the following year and so was presumed dead. Three of the 8 pairs remained intact and defended the same area in 1978, 1 was not observed again and the defended area taken over by neighbours, and 3 lost 1 bird of the pair. A single pair separated, each to take a new mate and become neighbouring pairs.