BIRDS O F M O T U O P A O I S L A N D , N O R T H L A N D , N E W Z E A L A N D

By R J . Pierce and G.R. Parrish Department of Conservation, PO Box 842, Whangarei

S U M M A R Y

A total of 38 species of birds were recorded during 5 visits to Motuopao Island in 1981-92. They comprised 17 species of seabird (including 6 breeding Procellariforme species), 3 shore-frequenting species and 18 land birds.

I N T R O D U C T I O N

Motuopao Island lies 350 m off Cape Maria van Diemen, Northland, at latitude 34°28'S (Fig. 1). The 30 ha island comprises basaltic lava overlain by

Fig. 1. Location map of Motuopao Island.

59 Tane, VoL 34, 1993

slopewash deposits and dune sands rising up to 110 m asl (Fred Brook pers. comm.). The central part of the island is moderate-gentle sloping, but the remainder (apart from the ridges) is steep, with tall cliffs on the western flank.

A broad band of exposed sand extends south-east to north-west across the low central saddle of the island, and a tongue of sand also extends from this band to high on the slopes in the south-west corner of the island (Fig. 1). These sands have scattered patches of vegetation including flax (Phormium tenax), Coprosma acerosa and Spinifex hirsutus. The bare sands give way to densely vegetated sands and slopewash deposits, with buffalo grass (Stenotaphrum secundatum) and flax predominating, the latter supporting small pockets of taupata (Coprosma repens), hangehange (Geniostoma rupestre), kawakawa (Macropiper excelsum) and other species (Forester, 1993).

The island was settled by Europeans operating the lighthouse for over 60 years before being abandoned in about 1940 (Shirley 1985). Some grazing occurred during this period and the vegetation was heavily modified (Forester, 1993).

On 26-27 November 1981 and 26-28 September 1988 general surveys were undertaken by the former Wildlife Service and by DoC respectively, the 1981 visit representing the first ornithological observations on this island. Observations on 1 - 4 February 1990, 14 - 17 November 1990 and 21-23 January 1992 occurred during an eradication programme for kiore (Rattus exulans) begun in October 1989.

M E T H O D S

Methods were approximately similar on all visits and involved day and night observations. Notes were kept of all birds seen ashore and offshore during the day, and their breeding status if known.

Daytime observations included counting of seabird burrows, and establishing a permanent quadrat in the black-winged petrel (Pterodroma nigripennis) colony. Night time observations involved using spotlights and/or torches to help identify the species present and to locate nesting burrows, e.g. by approaching vocalising birds and sites of activity especially when burrows were being cleaned out. Sites were usually revisited in the daytime in order to accurately map their locations. Individuals of three seabird species were weighed and measured.

R E S U L T S

A total of 38 species of birds was recorded on the island and/or offshore. They comprised seabirds (17 species), shore-frequenting birds (3) and land birds (18). The full list comprised:-

60 Tane, VoL 34, 1993

Blue penguin Eudyptula minor

Flesh-footed shearwater Puffinus carneipes

Bullers shearwater P. bulleri

Recorded (and breeding) during all visits with burrows being generally distributed across the island, but concentrated in the better vegetated areas. In November 1990, at least 90 individuals came ashore one night at Sandy Beach, probably the main access point for penguins. Some of the many young present in November 1990 were fully grown. Pair seen copulating September 1988.

Moderate numbers (up to 100 seen per hour) offshore in February 1990, November 1990 and January 1992.

Offshore in large numbers (hundreds seen per hour) in September 1988, February 1990 and January 1992.

Sooty shearwater P. griseus

Fluttering shearwater P. gavia

Offshore in February 1990 and ashore in small numbers in February and November 1990, and January 1992. Fewer than 20 occupied burrows were found high on the southern edge of the island in February 1990, (Fig. 2).

Offshore in large numbers (thousands) in September 1988, February and November 1990, and January 1992. One 128 g nesding found on 16 November 90 in a burrow on the steep open grassy north-eastern slopes of the island, is the only breeding record for Motuopao.

Little shearwater P. assimilis

Fewer than 10 offshore in February 1990.

Diving petrel Pelecanoides urinatrix

Grey-faced petrel Pterodroma macroptera

Ashore and breeding in September 1988 (40+ heard) and November 1990 (estimated 200+ pairs) in scattered colonies. The main breeding area was along the south-western ridge of the island where burrows penetrated dense buffalo grass (Fig. 2). Smaller concentrations were north and south-east of the lighthouse. On 14-17 November 90 chicks were well-grown averaging 183 g, cf. adults 148 g (Table 1). None were found in February 1990 but remains were found on Motuopao and the stack immediately to the north where an estimated 50 unoccupied burrows were present. Several offshore in January 1992.

Recorded ashore in moderate numbers (c 100 pairs November 1990) and breeding during the spring visits. Burrows were found along the southern and eastern edges

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of the island (mainly beneath shrubs) and around the lighthouse (Fig. 2). Young were small to medium sized in November 1990.

Table 1. Seabird weights, Motuopao Island

Species Age Date N Range Mean (g)

Black-winged petrel Adult Feb 1990 20 120-225 166.5

Black-winged petrel Adult Nov 1990 24 147-198 176

Black-winged petrel Adult Jan 1992 50 153-223 182

Diving petrel Adult Nov 1990 18 120-181 148

Diving petrel Pullus Nov 1990 7 145-229 183

White-faced storm petrel Adult Nov 1990 4 38-50 45

Note: A l l birds weighed in November 1990 and January 1992 were banded.

Black-winged petrel P. nigripennis

Breeding in the dune sands of the central part of the island, particularly in the higher altitude areas. In February 1990 the colony held an estimated 800-1000 pairs. A quadrat measuring 40 m x 57 m contained 109 occupied burrows; eggs were being incubated, with only one of 20 nests checked having hatched. In November 1990 500+ pairs were excavating burrows at night, but only 2 birds (both in one burrow) were seen ashore by day, although on all trips birds were occasionally seen flying over the colony by day. In January 1992 the colony had extended north-east to include the eastern ridge of the island but overall fewer occupied nests were found (e.g. the same 40 m x 57 m quadrat contained 77 nests, 71% of the February 1990 total). Many burrows had subsided, probably following heavy rain in the region on 10-11 January. Mean weight of adults captured off nests at night was only 166.5 g in February 1990 compared with 176 g in November 1990, and 182 g in January 1992 (Table 1).

White-faced storm petrel Pelagodroma marina

"Small numbers" were present in November 1981. In November 1990 several were seen and heard ashore in the upper reaches of the black-winged petrel colony and especially on the slopes extending southwards less than 100 m from the lighthouse (Fig. 2). Two one-egg nests

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were found beneath dense Leptocarpus near the lighthouse. From calls, the number of pairs present was estimated to be 20+. In January 1992 fewer than 10 were seen overhead at night in the south-west comer of the black-winged petrel colony.

Australasian gannet Tens to low hundreds seen offshore during all visits. Morus senator

Black shag Phalacrocorax carbo

Few (mainly singles) seen offshore in September 1988 and February and November 1990.

Pied shag P. varius

Few (mainly singles) seen roosting or fishing offshore during all visits.

Reef heron Egretta sacra

Not recorded in 1981 but singles seen on all trips 1988-92; mainly feeding in intertidal pools.

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Paradise shelduck Tadorna variegata

A single pair seen on all visits except January 1992 with breeding confirmed September 1988 (nest with 12 eggs in buffalo grass 20 m south of lighthouse) and November 1990 (one dead downy young).

Australasian harrier Circus approximans

Recorded during all but the 1981 visit. Several individuals (adults and immatures) commuting between the island and mainland. A nest of 4 eggs was found in November 1990. Diet included penguins and black-winged petrels, at least some of which had apparently been incapacitated first (e.g. by being caught in vegetation, broken wing). Over 35 harrier-chewed carcasses of black-winged petrels were seen in November 1990.

Variable oystercatcher Haematopus unicolor

A single pair seen during all but the 1981 visit. No evidence of breeding, although 3 flying birds were briefly seen together in January 1992. Commuting between Motuopao and the mainland was frequently seen.

Banded dotterel Charadrius bicinctus

Recorded during November 1981 only.

Southern black-backed gull Lams dominicanus

Small numbers (up to 10 together) seen during all visits. No evidence of breeding.

Red-billed gull L. novaehollandiae

Tens to hundreds seen per hour offshore during all visits. No evidence of breeding. Feeding mainly along southern shore.

Caspian tern Sterna caspia

Two offshore on 15 November 1990.

White-fronted tern S. striata

Recorded during November 1981 (nearly all adults) and in January 1992 when up to 100 were fishing the channel between the island and Cape Maria van Diemen.

Eastern rosella Platycercus eximus

Two seen briefly on 15 November 1990; not seen to land.

Skylark Alauda arvensis

Several recorded on each visit, breeding November 1990 (nest with 3 eggs).

Welcome swallow Hirundo tahitica

Moderate numbers (possibly up to 20) recorded during each visit.

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NZ pipit Anthus novaeseelandiae

Small numbers recorded (possibly 2-4 pairs) during each visit, breeding November 1990 (nest with 3 eggs).

Dunnock Prunella modularis

Frequently heard during all but the 1981 visit, breeding November 1990 (adult feeding juvenile).

Fantail Rhipidura fuliginosa

One on south side of island 0630 h, 23 January 1992.

Song thrush Turdus philomelos

Small numbers recorded during all but the 1988 visit, nesting January 1992. No anvils were found but the large numbers of Helix aspersa present (Parrish and Sherley, 1993) would provide ample food supplies. Anvils containing large numbers of Helix shells occur at Cape Maria van Diemen.

Blackbird T. merula

A few individuals recorded during all but the 1988 and 1992 visit.

Silvereye Zosterops lateralis

Two seen in November 1990. Common (30+) in January 1992, feeding on taupata berries; breeding suspected (carrying food).

Yellowhammer Embeinza citrinella

Moderate numbers (possibly 5-15 pairs) recorded during all visits. Territorial but no direct evidence of breeding was found.

Chaffinch Fringilla coelebs

Single recorded during September 1988 only.

Greenfinch Carduelis chloris

A pair recorded during November 1990 only.

Goldfinch C. carduelis

Single recorded during September 1988 only.

House sparrow Passer domesticus

Up to 30 recorded during September 1988, November 1990 and January 1992.

Starling Sturnus vulgaris

Up to 10 recorded during September 1988, November 1990 and January 1992.

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Myna Acridotheres tristis

Recorded during all visits, largest flock in November 1990 of 35+ birds.

DISCUSSION

With 6 species of breeding petrels, Motuopao Island has an unusually high diversity of seabirds. A seventh species, fairy prion (Pachyptila turtur) is listed as breeding (Lands and Survey unpub.), but probably stems from a misidentification during the 1981 visit (M Bellingham pers. comm.) The high number of species present is consistent with the known productivity of the Tasman Front which upwells off the northern New Zealand coast. There the cool water which carries concentrations of nutrients (especially phosphorous) leads to an enhanced primary production and high zooplankton biomasses (Bradford and Roberts 1978). Closer to Motuopao Island, tidal rips cause further mixing in the Cape Maria van Diemen-Cape Reinga area. These rich feeding areas attract seabirds from distant nesting areas, e.g. Buller's shearwater (Poor Knights) and flesh-footed shearwater (nearest breeding at Hen and Chickens). The large number of gannets seen offshore probably reflects the rich feeding areas and the proximity of the Three Kings Islands where c 10,000 pairs nest (Wodzicki et al. 1984).

White-fronted terns were seen on only one of the 1988-92 visits. This scarcity of sightings is consistent with recent trends elsewhere around Northland where numbers have declined dramatically in recent years (A Laing and R Pierce unpublished data).

The eradication of rats (kiore) from Motuopao Island in 1989-90 was undertaken primarily to protect Placostylus snails from predation, but it may enhance the island for birds. The smaller species of seabird, eg. white-faced storm petrel and diving petrel, are known to be impacted on by kiore (M J Imber and G A Taylor pers. comms.), so it will be interesting to see i f their breeding numbers increase. Land birds may also benefit through enhanced food supplies. Taupata was fruiting heavily in November 1990 and especially January 1992 when silvereyes were recorded in numbers and their breeding was suspected for the first time. Lizards have also responded positively to reduced predation pressure (Parrish and Pierce, 1993) and their increased biomass may eventually attract other predators e.g. kingfishers (Halcyon sancta), which are common on some northern islands.

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A C K N O W L E D G E M E N T S

Our thanks go to P Anderson, R Anderson, M Aviss, M Bellingham, F Brook, A Davis, D McKenzie, P Miller and T Shaw for helping with bird observations on Motuopao; G Taylor for reviewing the text, T Conaghan for draughting and J Roberts for typing the manuscript.

R E F E R E N C E S

Bradford, J .M. & Roberts P.E. 1978: Distribution of reactive phosphorous and plankton in relation to upwelling and surface circulation around New Zealand. New Zealand Journal of Marine and Freshwater Research 12: 1-15.

Forester, L . 1993: Vascular plants and vegetation of Motuopao Island, Northland, New Zealand. Tone 34: 33-44.

Lands and Survey: Te Paki. Unpublished pamphlet. Parrish, G.R. & Pierce, R.J. 1993: Reptiles of Motuopao Island, Northland, New Zealand. Tone 34:

53-58. Parrish, G.R. & Sherley G . 1993: Invertebrates of Motuopao Island, Northland, New Zealand. Tone

34: 45-52. Shirley, P. 1985: Ghost lighthouses of the Far North. Historic Places, September 1985. Wodzicki, K. , Robertson, C.J.R., Thompson, H.R. & Alderton, C.J.T., 1984: The distribution and

numbers of gannets (Sula serrator) in New Zealand. Notornis 31: 232-261.

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