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NEW ZEALAND ECOLOGY |
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FRUIT - EATING BIRDS |
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The silvereye Zosterops lateralis lateralis is also known as waxeye or white-eye, and to Maori as tauhou. The Zosterops genus containing 75 species belongs to the Zosteropidae family of 16 genera, of the Passeriformes order of perching birds.
The Zosterops lateralis lateralis subspecies is found on Flinders Island, Tasmania; Norfolk Island; and throughout New Zealand including the Chatham Islands.
Zosterops lateralis is spread throughout the South Pacific islands of Lord Howe Island, Loyalty Islands, Vanuatu and Fiji, and Australia and New Caledonia in addition to New Zealand.
The New Zealand subspecies Zosterops lateralis lateralis was first identified by Latham in 1801. It is not known exactly when silvereye first arrived in New Zealand, but first sightings were claimed in Fiordland in 1832. There is no record of them becoming established in Southland at about that time.
Silvereye probably arrived in New Zealand after a trans-Tasman Ocean crossing, or multiple crossings from Australia in prevailing westerly storms. They were observed in large flocks at Waikanai on the Kapiti Coast in 1856. |
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Silvereye assist an essential function in the ecological sustainability and restoration of forests by dispersing seeds and pollinating flowers. |
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They were not seen for two years at a time, and appear to have been restless without remaining in any one location for any long period, possibly migrating between the North and South Islands.
Silvereye were first observed breeding at Te Wairoa in Hawkes Bay in 1862, and thereafter reached Wanganui and Auckland, and further north the Bay of Islands in 1867.
It is often debated whether Zosterops lateralis lateralis is an authentic indigenous New Zealand bird. It arrived by natural migration, and became naturalized, as did so many other native birds. The question is the date of arrival, however, no time limit has been established for native species.
Zosterops lateralis lateralis, which is widespread throughout New Zealand, is listed as 'not threatened' on the New Zealand Threat Classification System. |
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References
Buller WL, A History of the birds of New Zealand, Sir Walter Lawry Buller, London 1888, The New Zealand Electronic Text Centre (Creative Commons Attribution-Share Alike 3.0 New Zealand Licence).
Clout MN, Hay JR, The importance of birds as browsers, pollinators and seed dispersers in New Zealand forests, New Zealand Journal of Ecology, Vol 12 (supplement) 1989.
Kelly D, Ladley JJ, Robertson AW, Anderson SH, Wotton DM, Wiser SK, Mutualisms with the wreckage of an avifauna: The status of bird pollination and fruit-dispersal in New Zealand, New Zealand Journal of Ecology, (2010) 34(1): pp 66-85.
Oliver WRB, New Zealand birds, AH & AW Reed, Wellington 1955. |
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Above - 1st image: Silvereye Zosterops lateralis lateralis enjoying the fruit of the native shrub poroporo Solanum aviculare, photo A. Walmsley, Copyright © Wildfocus.
2nd image: Silvereye in Coprosma, Maud Island, 1981, photo Rod Morris, Crown Copyright © Department of Conservation.
 See more on fruit-eating birds
 Hear the song of silvereye MP3 2,721K 2 min 53 sec.
Crown Copyright © Department of Conservation |
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A seed disperser of native plants ....
About 70 percent of the woody plants in New Zealand forests have fruits suited for vertebrate dispersal and, of these, most are probably dispersed by birds. About 70 percent of New Zealand's forest bird species, including most small insectivores, eat fruits [Clout & Hay 1989].
Across 32 studied species of native fleshy-fruited plants, the majority (84 percent) of fruit dispersal was by four birds - kereru, tui, bellbirds and silvereyes - although another 11 native and 7 introduced bird species took small quantities of fruit [Kelly et al. 2006].
The silvereye is a fruit-eating and nectar feeding bird that assists an essential function in the ecological sustainability, and restoration, of lowland forests by pollinating flowers and dispersing seeds.
It is a very resourceful and diversified feeder, also eating insects, especially after flowering and fruiting periods have ended, but sometimes alternating with fruit during the same meal.
Bellbirds and silvereyes swallow fruit in the 7-10 mm size class [Kelly et al. 2006]. Kohekohe Dysoxylum spectabile, which bears fruit with a diameter of 9mm, is the only known large native forest tree providing fruit for silvereye. It may be swallowed whole or just the flesh may be eaten.
The silvereye's gape, which is the width of the outside of the bill at the base of the upper mandible, is an average of 5.1mm, and a maximum of 6.3mm.
It has been observed swallowing whole supplejack Ripogonum scandens fruit which is 10.5mm in diameter, 4mm larger than it's maximum gape. The silvereye is the smallest of the birds eating whole fruit of a large tree, just 12cm in length and weighing less than 50 grammes.
Later in the summer fruiting season, a range of smaller trees and shrubs are food sources, including various Coprosma species, poroporo, makomako, mingimingi and other plants. |
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An important pollinator of native plants .....
Native birds have been recorded visiting the flowers of 85 native species, representing 5 percent of the total seed-plant flora, and 30 percent of the tree flora [Kelly et al. 2009].
Birds that pollinate the flowers of forest plants throughout New Zealand are the bellbird, stitchbird, red-crowned parakeet, yellow-crowned parakeet, saddleback, kaka, tui and silvereye.
In most of the mainland forests, the only birds that commonly visit flowers are bellbird, tui and silvereye, since stitchbird and saddleback are extinct on the mainland, and kaka and parakeets only rarely occur in large forest tracts.
A change in bird pollination since human arrival is the replacement of stitchbird which is only on a few offshore islands and protected mainland island areas, by the silvereye.
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The silvereye is one of the three principal pollinating birds in mainland native forests. |
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The silvereye is a prolific nectar feeder during the spring and summer flowering period, playing an important role in the pollination of kowhai, pohutukawa, rata, puriri and rewarewa forest trees, and many other native flowering plants.
Favourite sources of nectar for silvereye are flax Phormium cookianum and P. tenax.
Silvereye are widespread and, despite their recent arrival, are important for pollination of smaller flowers and dispersal of smaller fruits [Kelly et al. 2009].
Silvereye perform a valuable service in gardens and orchards, eating insects harmful to produce, including aphids, scale insects, and the diamond back moth.
Their value to the orchardist may be offset by their return during summer fruiting to feed, causing damage to a wide variety of soft fruit.
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