Download Breeding colonies distribution of White tern Lineage

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Lineage – Scientific methodology
Breeding distribution of White tern lineage
1. A “breeding colony” for New Zealand seabirds is defined as “any location
where breeding has been reported and is considered by the expert
compiling the species account to have occurred at that location at least
until 2002”.
2. An “occasional breeding colony” for New Zealand seabirds is defined as
“any location where breeding has been reported, but not necessarily
continuously nor during consecutive breeding seasons, and is considered
by the expert compiling the species account to have occurred at that
location during the last 30 years”.
3. Literature sources were searched for breeding distribution information.
a. Scientific papers, published texts, unpublished reports and
university theses available to the expert who prepared the
distributional layers.
b. Aquatic Sciences and Fisheries Abstracts for 1960-2009.
c. OSNZ News and Southern Bird for 1977–2009.
4. Other sources.
a. Nil.
5. The mapping of the White tern breeding sites at the Norfolk, Lord Howe
and the Kermadec Islands is based on a written description of their
location in Higgins & Davies (1996) and Veitch et al. (2004). The sites
have not been surveyed for mapping purposes, and the mapping
presented is based on the written descriptions of its location.
6. Summary
a. An expert scientist integrated information from the literature and
expert opinion, and produced hand-drawn distributional zones on a
template map. These maps were then digitised and imported into a
GIS software package as layers. The areas of the zones were
calculated, and the layers were linked to attribute and metadata
files.
b. The primary sources of breeding distribution data for White tern
were papers published in refereed journals.
c. The White tern is indigenous in New Zealand, with breeding
colonies on Norfolk Island, Lord Howe Island and Raoul Island, in
the Kermadec Islands, being the only known nesting sites (Higgins
& Davies 1996; Veitch et al. 2004). Elsewhere, it breeds widely on
tropical and subtropical islands in the Indian Ocean, Melanesia,
central tropical Pacific Ocean, and Hawaii (Higgins & Davies 1993;
del Hoyo et al. 1996).
d. Breeding populations were estimated at 2000-2500 pairs on Norfolk
Island in the mid 1980s and 60-100 pairs on Lord Howe Island in
1990 (Higgins & Davies 1996); at Raoul Island less than 10 pairs
bred in 1993-94 (Veitch et al. 2004). More recently, none has been
recorded breeding on Raoul Island, although they have been seen
prospecting for nest sites, and may already nest on steep cliff
faces, since 2004 (Baird 2006). The population is estimated at
more than 100,000 pairs worldwide (del Hoyo et al. 1996).
e. At Raoul Island, the population has probably declined over the past
100 years as a result of predation. White terns nest on relatively
low, near-horizontal branches (Higgins & Davies 1993) and this
habit makes the adults, eggs and chicks vulnerable to predation.
For example, Bell (1912) found as many as eight pairs, eaten by
cats, beneath one tree. In 1913, Iredale reported that the species
bred sparingly around the coast of Raoul Island, but Sorensen
(1964) reported that he found many pairs in the forest behind
Denham Bay during 1944. However, during 1993-94, only three
pairs were seen frequenting the Norfolk Pines near the
Meteorological Station and Low Flat. The maximum numbers of
White terns reported in recent years were up to 20 in flight in
March-May 1973, 16 in October 1974, and 10 flying around the
canopy of Low Flat Gully on 24 March 1994 (Veitch et al. 2004). If
the attempted eradication of cats and rats on Raoul Island during
2002 (Veitch et al. 2004) has been successful, then the population
of White terns should increase.
f. Numbers of breeding pairs on Norfolk Island may not have changed
recently (Higgins & Davies 1996). Breeding was first recorded on
Lord Howe Island in 1943, when 4-5 birds were observed; there
were about 50 birds present 3 years later and numbers have
fluctuated subsequently (Higgins & Davies 1996).
7. References
The following sources provided useful information on the breeding distribution of
this species. This is not an exhaustive list of all references to the species.
Baird, K. (2006). Kermadec Island seabirds. Pp. 13-15 in The state of New
Zealand’s birds 2006. Special report New Zealand’s seabirds. Ornithological
Society of New Zealand, Wellington. 16p.
Bell, R.S. (1912). Breeding habits of white tern (Gygis alba) on Kermadec Group.
Emu
12: 26-30.
del Hoyo, J.; Elliot, A.; Sargatal, J. (1996). Handbook of the birds of the world.
Volume
3, Lynx Edicions, Barcelona. 752p.
Higgins, P.J.; Davies, S.J.J.F. (1993). Handbook of Australian, New Zealand and
Antarctic birds. Volume 3, Oxford University Press, Melbourne. 1028p.
Iredale, T. (1913). Concerning the Kermadec Islands avifauna. Transactions and
Proceedings of the New Zealand Institute 45: 78-92.
Sorensen, J.H. (1964). Birds of the Kermadec Islands. Notornis 11: 69-81.
Taylor, G.A. (2000). Action plan for seabird conservation in New Zealand. Part B:
Non-threatened seabirds. Threatened species occasional publication No.
17, Department of Conservation, Wellington. 200p.
Veitch, C.R.; Miskelly, C.M.; Harper, G.A.; Taylor, G.A.; Tennyson, A.J.D. (2004).
Birds of the Kermadec Islands, south-west Pacific. Notornis 51: 61-90.