Vegetation composition and phenology of Mokoia Island, and ... · Abstract: Hihi (or stitchbird,...

19PERROTT, ARMSTRONG: VEGETATION OF MOKOIA ISLAND

New Zealand Journal of Ecology (2000) 24(1): 19-30 ©New Zealand Ecological Society

Vegetation composition and phenology of Mokoia Island,and implications for the reintroduced hihi population

John K. Perrott and Doug P. ArmstrongInstitute of Natural Resources, Ecology Group, Massey University, Private Bag 11222, Palmerston North,New Zealand (E-mail: [email protected])

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Abstract: Hihi (or stitchbird, Notiomystis cincta) is a rare honeyeater endemic to the North Island of New Zealand.Hihi were translocated from Little Barrier Island to Mokoia Island, Lake Rotorua, in 1994. Mokoia is a small(135 ha) island with secondary vegetation, so there was some doubt as to whether the island had sufficient diversityof fruit and nectar sources to support a hihi population. This paper reports data collected in the year after thetranslocation on the density, distribution and phenology of plants likely to be used by hihi. We address thefollowing questions. (1) How many hihi food plant species are on Mokoia? (2) How are the food plant speciesdistributed over the island? (3) Are there periods when flower and fruit sources are scarce and/or spatiallyconfined? (4) How might the availability of fruit and nectar change with succession or additional planting?There was always a minimum of 2-3 species providing nectar or fruit used by hihi. Most (16/21) of the speciesproviding nectar flowered during the hihi breeding period, from October-February, and most (9/16) of these werecanopy tree species. The greatest diversity of fruit sources was from March-May. August-September stood outas the period with the lowest diversity of fruit and flower sources, followed by June-July. While there was no timeof year when hihi clearly suffered from shortage of fruit and nectar, we suggest that they may be susceptible toshortages in future years at times when diversity of food sources is low. We recommend further planting that couldmake the island more suitable for hihi in the long term.__________________________________________________________________________________________________________________________________

Keywords: Food availability; hihi; Mokoia Island; New Zealand; Notiomystis cincta; phenology; vegetation.

Mokoia is in Lake Rotorua in the North Island(38°06'S, 174°55'E). With an area of 135 ha, it is thelargest island in a lake in New Zealand. However, it isthe smallest island where hihi have been released. It hassecondary forest, which has been regenerating forabout 50 years. Given the small size of the island, andthe youth of the vegetation, there was particular concernabout whether Mokoia had a sufficient diversity of fruitand nectar sources to support a hihi population. Mokoiahas a long history of Maori occupation. Maori grewcrops in the fertile soil for hundreds of years, and mostof the island was fired, cleared and terraced (Andrews,1992). Cultivation had stopped on Mokoia by about1950, and the island was made a Wildlife Refuge underthe Wildlife Act (1953).

Maori also modified Mokoia by deliberateintroduction of many native trees such as karaka(Cordynocarpus laevigatus2), whau (Enteleaarborescens), totara (Podocarpus totara), puriri (Vitexlucens), kowhai (Sophora spp.) and southern beech(Nothofagus spp.).

Introduction

Hihi (Notiomystis cincta1) were originally foundthroughout the North Island of New Zealand, and onat least the larger offshore islands. However, hihivanished from the North Island following Europeancolonisation, and survived only on Little Barrier Island(Oliver, 1955). There were several translocations ofhihi to Hen, Cuvier, and Kapiti islands from 1980-92,but these failed to establish self-sustaining populations(Rasch et al., 1996). The main hypothesis for thesefailures was insufficient year round supply of nectarand fruit, in conjunction with competition fromother more dominant honeyeaters, bellbirds(Anthornis melanura) and tui (Prosthemaderanovaeseelandiae).

______________________________________________________________1Nomenclature of birds follows Turbott (1990).2Nomenclature of plants follows Allan (1961), Moore andEdgar (1970), Connor and Edgar (1987), and Webb, Sykesand Garnock-Jones (1988).

20 NEW ZEALAND JOURNAL OF ECOLOGY, VOL. 24, NO. 1, 2000

Europeans arrived on Mokoia not long after 1830(Andrews, 1992). European missionaries planted exotictree species like pine (Pinus radiata), poplar (Populusspp.) and a variety of fruit trees. Europeans alsointroduced cattle (Bos taurus3 ), goats (Capra hircus),sheep (Ovis aries), horses (Equus calballus), pigs (Susscrofa), and cats (Felis catus). Norway rats (Rattusnorvegicus) and mice (Mus musculus) were introducedaccidentally, and were abundant on Mokoia by 1840(King, 1984). There are no reports of possums(Trichosurus vulpecula) or mustelids ever being presenton Mokoia. Pheasants (Phusianus colchicus) werefarmed as a commercial venture from 1952-56, andgrain fed to pheasants probably encouraged irruptionsof the rat and mouse populations (Beveridge and Daniel,1965). Weka (Gallirallus australis) were translocatedto Mokoia sometime in the 1950s, and are still there. Itis not clear when the Australian crested wattle trees(Albizia lophantha) were planted. These are notabundant, but provide an important nectar source forhihi in winter.

Goats were introduced in 1985 to control blackberry(Rubus fruticosus) on the eastern flat, which was fencedoff. However, the goats escaped into the bush andbegan browsing the regenerating forest. By 1989 theunderstory was open with no further regeneration ofcanopy species taking place. During 1989-90 theDepartment of Conservation successfully eradicatedrats and goats from Mokoia. An attempt to eradicatemice in September 1996 was unsuccessful.

Since the rats and goats were eradicated, toutouwaior North Island robin, (Petroica australis), and tieke orsaddleback, (Philesturnus carunculatus), and hihi haveall been introduced to Mokoia. Nine other native birdspecies are present, having either survived humanoccupation or naturally re-colonised the island. Lizardswere thought to be absent, but speckled skinks(Oligosoma infrapunctatum4 ) were discovered on theisland in 1993.

The first restoration attempts, in the mid 1960s,involved planting thousands of native tree saplings andferns. Most of these were probably eaten by rats, andthe planting had negligible effect on the presentvegetation (Wallace, 1993). The island’s vegetation isnow composed largely of understory species such asfive-finger (Pseudopanax arboreus), kawakawa(Macropiper excelsum), mahoe (Melicytus ramiflorus)and rangiora (Brachyglottis repanda). The vegetationis low and scrubby on the ridges, particularly near thesummit, but there is a closed canopy with an open forestfloor in gullies and near the lake shore. The canopyspecies are largest in gullies and bush edges, where

mahoe, kohuhu (Pittosporum tenuifolium) and treefern(Cyathea spp.) dominate. On the south-facing slopesmamaku (Cyathea medullaris) is the dominant canopyspecies. Amongst the patches of bracken (Pteridiumaquilinum) and blackberry on the north-facing slopesthe dominant species are cabbage tree (Cordylineaustralis) and five-finger.

When hihi were translocated to Mokoia Island in1994 (Armstrong et al., 1999), we developed aprogramme to directly test whether this new populationwas limited by nectar and fruit availability, and if so,whether this was due to competition from tui (there areno bellbirds on Mokoia). We collected data in threecategories during each of the first 14 months after hihiwere released. (1) We did supplementation experimentsto determine what times of year, if any, that condition,survival or reproduction of hihi was limited bycarbohydrate availability (Perrott 1997; Armstronget al., 1997). (2) We collected data on vegetationcomposition, fruiting phenology and floweringphenology to determine if times of food limitation werecorrelated with abundance or diversity of fruits andflowers (reported in this paper). (3) We collected dataon energetic quality of fruits and flowers, foraging byhihi, and interactions with tui, to determine if theenergy intake rates achieved by hihi closely matchedseasonal changes in abundance and diversity of flowersand fruits.

As well as addressing the question of food shortagein the year after release, the data in this paper also allowus to predict how seasonal patterns of nectar and fruitavailability may change with succession. These dataprovide a detailed case study of the vegetationcomposition and phenology of an island undergoingnatural revegetation, and provide a comparison forfuture vegetation studies on Mokoia.

Methods

Vegetation Surveys

We surveyed the distribution and density of all plantspecies likely to be used by hihi. Initially we surveyed24 target species by noting all species hihi had beenseen using on Little Barrier and Kapiti Islands (Godley,1979; Angehr, 1984; Castro 1995), and comparing thisto the list of plant species recorded on Mokoia (Beadleand Ecroyd, 1990). We recorded the phenology ofthese 24 species throughout the study. During theproject we also saw hihi feeding on kawakawa fruits,deadly knightshade (Solanum nigrum) fruits, and akeake(Dodonaea viscosa) flowers. We added these to ourtarget species, making 27 in total.

The island was divided into 28 grid squares (200m x 200 m each). Grid points were determined with a

______________________________________________________________3Nomenclature of mammals follows King (1990)4Nomenclature of lizards follows Gill and Whitaker (1996)


Table 1. Plant species known or likely to be used by hihi (from Godley, 1979; Angehr, 1984; Castro, 1995, and observationsduring this study). Species found on Mokoia and species included in the vegetation survey are indicated. The species not includedin surveys were either discovered to be used by hihi late in the project, or or are so rare that flowering and/or fruiting individualswere not found.__________________________________________________________________________________________________________________________________

(a) Nectar taken Found Surveyed (b) Fruits taken Found Surveyed__________________________________________________________________________________________________________________________________

Albizia lophantha X X Alseuosmia macrophyllaAlectryon excelsus Aristotelia serrata X XAlseuosmia macrophylla Ascarina lucidaAristotelia serrata X X Astelia spp. X XAstelia spp. X X Coprosma dodonaeifoliaBeilschmiedia tawa Coprosma grandifolia X XCarpodetus serratus Coprosma lucida.Chamaecytisus palmensis Coprosma macrocarpaClematis vitalba X Coprosma repensClianthus spp. Coprosma rhamnoidesCordyline australis X X Coprosma robusta X XCoriaria arborea X X Coriaria arborea X XCorynocarpus laevigatus X X Cyathodes fasciculataCyathodes spp. Cyathodes juniperinaDodonaea vicosa X X Freycinetia bauerianaDracophyllum spp. Fuchsia excoticata X XDysoxylum spectabile X X Gahnia setifoliaEarina autumnalis X X Geniostoma rupestre X XElaeocarpus dentatus Griselineia littoralis XEntelea arborescens X Ixerba brexioidesFuchsia excorticata X X Macropiper excelsum XGeniostoma rupestre X X Melicytus ramiflorus X XGriselinea littoralis Muehlenbeckia australis X XHebe spp. X Myoporum laetumHedycarya arborea Myrsine australis X XHoheria populnea Myrsine salicinaKnightia excelsa X X Nestegis lanceolataLaurelia novaezelandiae Passiflora tetrandraMelicytus ramiflorus X X Pennantia corymbosaMetrosideros excelsa X X Phytolacca octandraMetrosideros fulgens Pseudopanax arboreus X XMetrosideros perforata Pseudopanax crassifoliusMetrosideros robusta X X Pseudopanax discolorMetrosideros white flower X X Pseudopanax edgerleyiMetrosideros umbellata Pseudopanax lessoniiMida salicifolia Pseudowintera axillarisMyoporum laetum Ripogonum scandensMyrsine australis X X Rubus cissoides X XMyrsine salicina Schefflera digitata X XNestegis lanceolata Solanum nigrum X XPseudopanax arboreus X XPassiflora tetrandraPeraxilia spp.Toronis toruPhormium tenax X XPittosporum crassifoliumPittosporum eugenioidesPittosporum tenuifolium X XPittosporum umbellatumPrumnopitys ferrugineaPseudopanax crassifoliusRhabdothamhus solandriRhopalostylis sapidaRipogonum scandens XRubus cissoides X XSchefflera digitata X XSophora spp.Syzgium maireVitex lucensWeinmannia racemosa X XLupinus luteus X

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compass and measuring tape, and the centre of eachgrid marked with flagging tape. Some grids werepartially in the lake. If the central point was in the lakethe flagging tape was placed on the nearest point on theshoreline. Each month, from September 1994 (whenhihi were released) until November 1995, we selecteda random sample point within each grid. The samplepoint in each grid was determined by measuring aspecific distance from the central grid point at a specificcompass bearing. If the random point was in the lake,we disregarded that sample. Therefore, there was nobias for or against lake-edge habitat.

Once the sample point was established, a samplearea of 3 m radius was measured out using measuringtape and a telescopic pointer. During this study157 points were sampled, each 28.3 m2, giving a totalsampled area of 4443 m2. In each sample area wecounted the number of individuals of each plant specieson the target list. A ramet was considered to define anindividual plant, i.e., we counted the number of trunksnot joined above the ground. Plants were counted onlyif the trunk was within the sample area at ground level.Plants too small to be flowering were not counted(below about 2 m height for most species).

Sample areas were classified into one of fivehabitat types based on topography: (1) gully, (2) slope,(3) ridge top, (4) within 5 m of track, and (5) within12 m of the shore. This allowed us to comparespecies composition and densities among these habitattypes.

Measuring fruiting and flowering phenologies

The number of fruits or flowers was estimated for eachtarget plant in the sample area every two weeks, anddata was pooled on a monthly basis. Different estimationmethods were used, depending on the species andsituation:

If the plant had less than about 300 flowers orfruits, then all were counted. If the plant had abundantflowers and/or fruits distributed around the peripheryof the plant, a 16 cm x 16 cm sampling quadrat wasused. All fruits or flowers were counted in one quadrat,and the surface area of the plant estimated from itsheight and width. To estimate the total number of fruitsand/or flowers, we multiplied the count by the plant’stotal surface area divided by the surface area of thequadrats sampled. Species in this category includedMuehlenbeckia australis and white rata (Metrosideroswhite flower spp.).

If fruits and flowers were not confined to theperiphery, the plant was divided into branches ofequivalent area, and five branches selected at random.The fruits or flowers were counted for each selectedbranch unit or estimated with the quadrat. The average

per branch was calculated, and multiplied by the totalnumber of branches. Species in this category includedmahoe, Coprosma spp., and wineberry (Aristoteliaserrata).

If the species had fruits or flowers in inflorescences,we counted the number of inflorescences per tree.Individual flowers or fruits were counted on fiverandomly chosen inflorescences. The mean number offlowers or fruits per inflorescence was then multipliedby the total inflorescence count to estimate the numberof flowers or fruits on the tree. Species in this categoryincluded pohutukawa (Metrosideros excelsa), five-finger and, pate (Schefflera digitata).

Only open flowers were counted, and not buds.Old flowers not producing nectar were not counted,and were removed by shaking the branch. All fruitswere recorded, ripe fruit being given as a proportion ofthe total count. For dioecious species such as mahoeand five-finger, we recorded genders of all individualswhenever possible. Sexing was not possible for plantswithout flowers or fruits.

Figure 1. Number of individuals per hectare for plant speciesproducing fruit or nectar likely to be used by hihi on Mokoia.Calculations are from 157 random sample areas of 28.3 m2.


Results

Vegetation density, distributionand successional effects

Most species used by hihi are trees or shrubs, which canbe divided into three successional categories: canopytrees, sub-canopy hardwood trees/shrubs, and sub-canopy softwood trees/shrubs (Tables 1, 2). Hihi alsoused some epiphytes, which occur only under closedcanopy, and flax, which only occurs in open areas in afew patches on Mokoia. However, almost all hihiforaging observed on Mokoia was on the trees andshrubs (Perrott, 1997). Of the 27 species surveyed, sub-canopy species such as mahoe, kawakawa, five finger,pate, and Coprosma spp. are clearly the most abundantspecies (Fig. 1). The distributions and relativeproportions of plant species in the three successionalcategories are described below.

Canopy trees

Canopy trees are larger than sub-canopy trees/shrubs,and this partially accounts for their lower abundance(Table 2, Fig. 2). Most of the fruiting and floweringindividuals of these species were quite large. There arealso abundant seedlings and saplings of most of thesespecies, but few of intermediate size, i.e., 2-3 m tall.Most provide nectar used by hihi.

Mahoe is not normally thought of as a canopyspecies. However, it is a common canopy species on allparts of Mokoia and is therefore considered a canopyspecies here. Mahoe makes up 49% of all canopy treescounted. Without mahoe in this category, the canopyspecies make up only 13.6 % of all plants countedduring this study. The large mahoe trees are found ingullies, track areas and near the shoreline, and producerelatively few flowers and fruits (Fig. 2).

Table 2. Plant species used by hihi on Mokoia, divided into successional and size categories. The percentages show the overallrelative abundances of each species in terms of individuals per hectare (see Figure 1). The totals give the combined percentabundance for all species in each category.__________________________________________________________________________________________________________________________________

Category Species % Part used__________________________________________________________________________________________________________________________________

Canopy trees Melicytus ramiflorus 13.0 FruitPittosporum tenuifolium 5.8 FlowersCordyline australis 3.6 FlowersWeinmannia racemosa 1.3 FlowersMeterosideros excelsa 1.1 FlowersCorynocarpus laevigatus 1.0 FlowersDysoxylum spectabile 0.5 FlowersMeterosideros robusta 0.2 FlowersKnightia excelsa 0.1 FlowersTotal 26.6

Sub-canopy hardwood Aristotelia serrata 3.0 Flowers, Fruittrees/shrubs Fuchsia excorticata 1.8 Flowers

Myrsine australis 0.9 Flowers, FruitAlbizia lophantha 0.4 FlowersLeptospermum ericoides 0.1 FlowersTotal 6.2

Sub-canopy softwood Macropiper excelsum 27.4 Fruittrees/shrubs Pseudopanax arboreus 15.0 Flowers, Fruit

Schefflera digitata 8.1 FruitCoprosma spp. 8.0 FruitGeniostoma rupestre 5.0 Flowers, FruitDodonaea viscosa 1.0 FlowersCoriaria arborea 0.9 FruitTotal 65.4

Monocots and epiphytes Muehlenbeckia australis 1.0 FruitPhormium tenax 0.4 FlowersRubus cissoides 0.2 Flowers, FruitAstelia spp. 0.2 Flowers, FruitEarina autumnalis 0.1 FlowersMeterosideros white flower 0.1 FlowersTotal 1.8

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Figure 2. Distribution and the proportional abundance of 25 plant species shown in Table 2. Kawakawa and rewarewa areexcluded to make the graphs easier to read. Kawakawa is a superabundant species found in all localities, while rewarewa is rarewith only two individuals recorded. Plant species have been grouped into five successional categories, canopy trees, sub-canopyhardwood tree/shrubs, sub-canopy softwood tree/shrubs, and monocotyledons, epiphytes and lianes. Plant species proportionswithin these categories are compared among five habitat types. Cabbage tree and mahoe are placed in the canopy tree categorybecause these are major emergent tree species on Mokoia.


Kohuhu is the second most abundant canopy treespecies on Mokoia, and is an important nectar source inspring. Kohuhu is found all over Mokoia, but especiallyin gullies, particularly in the west and northwest portionsof the island. However, many large kohuhu have diedand fallen over.

Pohutukawa is a key nectar source in summer. It isconfined to a narrow strip around the shore, particularlyin the northwest, west and southwest where the shoreis rocky and steep. Most trees are 10-12 m and haveover 100,000 flowers at their peak. However, becausepohutukawa are few and far between, the total flowercounts for December and January are lower thanFebruary (Figs. 1, 3).

Kohekohe is confined to an area of about 5 ha at thesouth of the island, and may be a key nectar source inwinter. The ‘kohekohe-karaka forest’ in this area isprobably the most mature vegetation type on the island(Wallace, 1993). There are many seedlings and saplings,but most of the flowering kohekohe are 8-10 m tall.Cabbage trees are found mainly on the north-facingslopes. However, the larger trees are found away fromthe north-facing slopes, around the lower gully areas.There are many dead trees, but recruitment of cabbagetree juveniles appears quite high. Rewarewa are rare,and only one was counted in the vegetation surveys.There are trees on the upper slopes and the south sideof the island, and some seedlings and juveniles.

Sub-canopy hardwood trees/shrubs

This category contains the lowest number of species,but has species that may be important for both nectarand fruit. Wineberry is the most abundant, and its fruitsprovide the richest packets of energy on Mokoia (Perrott,1997). However, the fruits are not abundant because

most trees produce few fruits. Most are spindlyjuveniles, and these are found all over much of theisland. There are a few very large trees, some of whichhad thousands of fruit.

Fuchsia is a widespread species on Mokoia, and isan important nectar source in spring. Most are smalltrees or shrubs. There are mature trees exceeding 12 min some gullies, but these large trees tend to have fewbranches and produce few flowers. Fuchsia is found inall five habitat types, but are most common in gulliesand least common on the shoreline. Fuchsia is possiblydying off in some locations along with kohuhu. Albiziais not abundant, but is a key nectar source in winter.Albizia trees are scattered in small patches around theisland from shore to ridge top. The largest trees (6-9 m)are found along the west side and in the south-easternportion.

Sub-canopy softwood trees/shrubs

These are early successional species, and are clearlythe most widespread and abundant hihi food plants.These are important fruit species, and all except akeakeprovide fruit that hihi eat. Five finger and pate alsoprovide flowers. Five-finger is the most widespreadand abundant species, and is a key source of bothflowers and fruit. It is particularly dense around themidline, especially on northern slopes and ridge areas.Five-finger flowers have little nectar per flower, but

Table 3. Comparison of the number of recorded hihi foodplant species in flower and fruit each month on Kapiti Island(Castro, 1995) and Mokoia Island (this study).______________________________________________________________

Kapiti Island Mokoia IslandMonth Flowers Fruits Total Flowers Fruits Total______________________________________________________________

January 5 15 20 15 9 24February 5 12 17 12 11 23March 3 6 9 6 12 18April 2 6 8 6 13 19May 3 2 5 2 10 12June 4 3 7 3 8 11July 6 3 9 3 6 9August 6 2 8 2 5 7September 6 6 12 6 4 10October 7 11 18 12 1 12November 9 13 22 13 3 16December 10 16 26 16 5 21Total 33 17 50 21 13 34______________________________________________________________

Figure 3. Number of hihi food plant species in fruit and flowereach month on okoia (top), and total number of flowers andfruits per hectare for those species (bottom).


Table 4. Plant species that could be planted on Mokoia to increase the diversity of nectar and fruit sources.__________________________________________________________________________________________________________________________________

Species providing nectar Species providing nectar in Species providing fruit inin spring and summer autumn and winter spring and summer__________________________________________________________________________________________________________________________________

Knightia excelsa1 Vitex lucens Myrsine salicinaPennantia corymbosa Syzygium maire Passiflora tetrandraElaeocarpus dentatus Dysoxylum spectabile 1 Hedycarya arboreaSophora microphylla Metrosideros spp. 1 Pseudopanax edgerleyiPittosporum crassifolium Coprosma lucidaDodonaea viscosa 1

Mida salicifoliaToronia toruAlectryon excelsus 2

Alseuosmia macrophylla 3

Pittosporum umbellatum__________________________________________________________________________________________________________________________________

1Found on Mokoia, but neither common nor widespread2Currently one tree near the hotpool3A small number were planted in one part of Mokoia in 1994

compensate through abundance and high flowerdensities (Castro and Robertson, 1997).

Pate is abundant, and an important fruit source. Itis most commonly found as an understory plant ingullies and southern slopes dominated by mamaku, andis least abundant in open areas like ridge tops (Fig. 2).Some large individuals (6-7 m) are found in the lowerregions of the island where the canopy is highest.Coprosma spp. are also abundant, and are an importantfruit source. Coprosma are evenly distributedthroughout all habitat types, but are most abundantaway from gullies. Like wineberry, most Coprosmaplants sampled were young individuals (under 1.5 m)that have probably grown since the goats were eradicatedin 1989-90.

Other species

There are several epiphytes and lianes on Mokoia thatare sometimes used by hihi (Table 1), but the only onelikely to be important to hihi is Muehlenbeckia australis.M. australis is always an edge species, but is commonin several parts of Mokoia. Flax (Phormium tenax) isscattered over a few locations, mostly on ridge tops andalong the shoreline (Fig. 2).

Fruiting and flowering phenology

The number of species in flower was highest betweenOctober and the end of February (Fig. 3), whichcoincided with the hihi breeding season. All but one ofthe 21 nectar-providing species surveyed floweredduring this period (Fig. 4). The number of species infruit was highest from March-May. Wineberry, pate,kawakawa, five-finger, cabbage tree, hangehange(Geniostoma rupestre),Muehlenbeckia, tutu (Coriariaarborea), and most Coprosma had fruit during this

period. August and September were the months withthe fewest species in fruit or flower.

While the number of species flowering peaked inDecember-January, the total number of flowers did notpeak until February. There are two reasons for this.First, during summer most flowering species providemany flowers per tree, but occur in low density and/orare confined to particular habitats such as gullies or thelakeshore (Fig. 1). These species include karaka,pohutukawa, kamahi (Weinmannia racemosa) andrewarewa (Knightia excelsa). Secondly, widelydistributed sub-canopy species such as mahoe and patereached peak flowering in February.

Flower counts dropped dramatically after summer,and most species stopped flowering in March or April.There were twice as many species providing fruits thanflowers in March and April, and five times as many byMay. There were more species fruiting than floweringfor most of the hihi non-breeding season (March-August). However, fruit and flower counts were bothrelatively low in June and July (Fig. 3).

In early winter, only kohekohe (Dysoxylumspectabile) and Albizia were providing useful nectarsources, and neither is abundant on Mokoia. Fuchsiaexcorticata and five-finger start flowering in July, withmale five finger starting before female five finger.During July and August birds had few flowers availableother than five-finger, Albizia and Fuchsia. However,total flower counts were high in August due to fivefinger, which had a high density of flowers all overMokoia during August-September.

The Albizia/five-finger flowering period finishedin spring. Fuchsia and kohuhu then provided most ofthe available nectar, but their flowers were less abundantthan five-finger. While the number of species in flowerincreased in October and November, there was a largedrop in the total number of both flowers and fruits(Fig. 3).


Figure 4. Fruiting and flowering phenologies for most plant species likely to used by hihi on Mokoia. Four plant species in thevegetation survey were excluded from the phenology study: manuka, bushlawyer, rata, and deadly knightshade. These specieswere either discovered to be used by hihi after the start of the phenology study, or are so rare that flowering and/or fruitingindividuals were not found.


In October five finger was the only remainingspecies in fruit, while there were 11 species flowering.October was a crossover period, when most specieseither started flowering (e.g., karaka, kohuhu, rewarewa,hangehange Geniostoma rupestre) or finished fruiting(e.g., pate, Coprosma, tutu, and Muehlenbeckia). AfterOctober the flower count per hectare increased sharply.

Discussion

Our supplementary food experiment showed that thecondition and survival of hihi were not limited bycarbohydrate availability from January-October(Armstrong and Perrott, 2000). It is possible thatreproduction (from October-February) was limited bycarbohydrate availability, but the results are variableand unclear. While there is no clear evidence ofcarbohydrate shortage in the period studied, there weretimes when hihi probably relied on one or two plantspecies. August-September was the period with thelowest diversity of nectar and fruit sources, suggestingthat five-finger (which has peak flowering in August-September) is a key species. Kohekohe and Albiziawere also important nectar sources, being the only twoavailable in early winter. Fuchsia may also have beenimportant during October, when most species were juststarting to produce flowers. Pate and Coprosma spp.provided fruit through winter and early spring, andwere key fruit sources.

There can be great variation in phenology fromyear-to-year (Castro, 1995). The timing of flowering,abundance of flowers, and degree of synchrony amongspecies will be different on Mokoia in subsequentyears, and it is likely that there will be some years with“crunch” periods when food is particularly scarce.Such crunches may be relatively rare, but can be keyevents in the ecology of honeyeater populations (Ford,1991). By identifying periods when hihi may bedependent on one or a few species, we can predict theperiods when crunch periods are most likely to happen.

Crunch periods may be more common and/orpronounced on small islands such as Mokoia. Incomparison to Mokoia, Little Barrier Island (3076 ha)has a much wider range of habitats. Due to the higheraltitude on Little Barrier, there may also be someseasonal variation between low-altitude and high-altitude habitats that birds can exploit.

Of the 102 plant species used by hihi on LittleBarrier, hihi take nectar from 27 species and fruit from34 species (Angehr, 1984; 1986). Kapiti Island has 75of these species, with hihi taking nectar from 33 speciesand fruit from 17 (Castro, 1995). This is more thantwice the species available on Mokoia (27), but likeKapiti hihi, Mokoia hihi take nectar from more species(21) than fruit (14) (Perrott, 1997). Castro (1995) noted

that preferred fruiting species may be rare or absent onKapiti, forcing hihi to forage more on invertebrates andlow-grade nectar sources. In comparison to Kapiti,Mokoia has about twice the number of fruit sourcesfrom March-July, the months when hihi mostly takefruit on Little Barrier (Table 3) (Angehr, 1984; Raschand Craig, 1988). Kapiti shows a drop in fruitingspecies during these months, but has more fruit sourcesavailable in spring and summer compared to Mokoia.

Castro (1995) noted that 13 flowering specieswere available on Kapiti during the hihi breedingperiod, but that most were rare, confined or of lowquality, e.g., pohutukawa and Fuchsia. On Mokoiathere were a total of 16 nectar sources available duringthis time. While half of these species are rare, eight ofthem are reasonably abundant including pohutukawaand Fuchsia.

The vegetation on Mokoia Island is regenerating,another contrast between it and Little Barrier is thatseasonal patterns of fruit and nectar availability willchange with succession. At present, most of the nectarsources for hihi are canopy species or hardwood sub-canopy species. In contrast, most of the fruit sourcesare softwood subcanopy species which are the earliestsuccessional species. A shift toward later successionalstages may decrease fruit availability. However, this iscomplex and will certainly not happen in the nearfuture.

The immediate future will mainly see a maturationof subcanopy species, rather than a shift to canopyspecies. In addition, fruit production of some specieswill change with succession. Both pate and mahoemostly produce fruit in closed-canopy environments.Therefore, the total fruit production of these species islikely to increase even if their abundance decreases. Incontrast, most Coprosma spp. produce more fruit inhigh light environments, so may decrease their totalfruit production with succession.

Table 4 lists 20 species that could be planted, someof which are already found on Mokoia in low numbers.These species are all found in the Rotorua area, andthey are all suitable for lowland forest.

Planting recommendations

It is possible that Mokoia may be less suitable for hihiif it were a climax habitat. This would occur if thealready existing canopy species, such as seral mahoe,were to succeed much of the area presently occupied bysubcanopy species such as five-finger.

Without additional planting, species abundanceand/or diversity on Mokoia may decrease with time asthe forest matures. If the early successional species(e.g., Albizia and five-finger) are replaced by speciesthat fruit or flower at different times then crunchperiods could become more pronounced for the birds.


The diversity of habitats may also decrease. Therefore,problems associated with small islands may becomemore pronounced with succession to climax forest.This could partly explain why hihi were only recordedhistorically on the mainland and larger offshore islands.

Unlike Tiritiri Matangi, Mana, and Motutapuislands, there is currently no planting programme forMokoia. However, planting is being considered as partof the management plan for the island being developed.Like planting programmes on the other islands, plantingon Mokoia is likely to be oriented towards providingfruits and flowers for birds. Further research would beneeded to confirm if species were previously found onMokoia, and to select genetic stock for planting.

The species selected would diversify the supply offruit and nectar sources on Mokoia to prevent a naturaldecrease in diversity with succession. It may also beimportant to monitor key species that are rare or spatiallyconfined, such as kohekohe. Albizia also falls in thiscategory. However, it is being removed from the islandbecause it is an exotic, and this is probably reducing thequality of the island for hihi. If the main goal of plantingwere to conserve hihi, the best strategy would probablybe to conserve Albizia and plant more exotics such asEucalyptus spp. and Acacia spp. However, any plantingmust fit the overall cultural and restoration objectivesfor Mokoia. The objectives are being developed by theMokoia Island Trust Board, which represents thetraditional Maori land owners.

Acknowledgements

We are grateful to Ed Minot, Alastair Robertson, IsabelCastro, Alan Perrott and Kimberley Perrott for theiradvice and instruction. Thank you to Peter Koole, JonRoygard, Ben Hagglund, John Ewen, Martin Aldridge,Ian Watson, Halema Flannagan, Jay Jury, Bill Hansby,Brooklyn and Carolyn Povy, and Dino and Weavil forhelp in the field. Ngaroto Cruises helped by storing ourvehicles and running several errands for us. Our researchwas done with permission from the Mokoia IslandTrust Board and the Department of Conservation.Financial support was provided by the World WideFund for Nature and the Todd Foundation.

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