P. 58: Crested Ibis © XI ZHINONG/BP Seychelles Magpie-robin © CATH MULLEN Kirtlands Warbler © DOUG WECHSLER/VIREO P. 59: Clipperton Island © BERNIE TERSHY White-headed Duck © TONY MARTIN/BIRDLIFE
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By definition, Globally Threatened Birds face a high risk of extinction in the wild, but this does not mean that their extinction is inevitable. Species with very small populations face certain particularly acute threats, including genetic and social complications and extreme environmental events. Nevertheless, with sufficient resources, careful management and a sound understanding of their ecology and requirements, even Critically Endangered species can be saved (see box 1), as shown by recent examples such as the Crested Ibis, Mauritius Kestrel and Seychelles Magpie-robin.
Back from the brink: two Critically Endangered species saved from extinction
Black Robin Petroica traversi is endemic to the Chatham Islands (New Zealand). The rescue of this species from its tiny refuge on Little Mangere Island is one of the most remarkable successes in species conservation1,2. Following human settlement of the islands, the species declined rapidly as its forest habitat was lost and degraded, and due to predation by introduced rats and cats. In 1976, when the population had declined to just seven birds, the remaining individuals were relocated to nearby Mangere Island, where thousands of trees had been planted to provide suitable habitat. Nevertheless, by 1980, numbers had fallen to five (three males and two females)the smallest population of any bird species for which precise figures were known. Nest protection, supplementary feeding, and a cross-fostering programme (with the congeneric Tomtit P. macrocephala) were then established, and the population began to recover steadily. Individuals were later introduced to South East Island, and by 1989 the population had topped 100 individuals2, at which point management ceased. The population continued to rise until carrying capacity was reached in the late 1990s, since when it has been stable at around 250 birds3.
Intensive management has led to the recovery of both Black Robin and Rarotonga Monarch Black Robin Rarotonga Monarch
Number of individuals
Species can be saved from extinction, but this requires sound research, careful co-ordination of effort and, in some cases, intensive management.
Even species on the brink of extinction can be saved
Recovery plan initiated
Cross-fostering programme begun
50 0 1970
Rarotonga Monarch (or Kakerori) Pomarea dimidiata is endemic to the Pacific island of Rarotonga (Cook Islands). Although common in the mid1800s, the species subsequently declined rapidly, and following the collection of a few specimens in the early 1900s, was not recorded again until 1973. In 1983, 21 birds were discovered, and a survey in 1987 estimated the population at 38 individuals, but declining4. A recovery plan was prepared in 1988, and implementation began later that year. Intensive control of predators (particularly black rats Rattus rattus) reduced adult mortality from 24% to 9%5, with nesting success increasing from 15% to 63%4. By 2000, the population on Rarotonga had reached 221 individuals (see figure), and between 20012003 30 young birds were transferred to the rat-free island of Atiu (200 km north-east of Rarotonga) in an apparently successful attempt to establish a second insurance population5. SOURCES 1. Aikman et al. (2001) Chatham Islands threatened birds: recovery and management plans. Wellington, New Zealand: Department of Conservation. 2. Butler & Merton (1992) The Black Robin:
saving the world’s most endangered bird. Auckland, New Zealand: Oxford University Press. 3. D. Merton in litt. (2004). 4. Robertson et al. (1994) Conserv. Biol. 8: 1078–1086. 5. H. Robertson & E. Saul in litt. (2004). ACKNOWLEDGEMENTS Information kindly provided by Hilary Aikman, Rod Hitchmough, Don Merton and Hugh Robertson (New Zealand Department of Conservation) and Ed Saul (Takitumu Conservation Area, Cook Islands).
Intensive habitat management has led to a spectacular increase in Kirtlands Warbler
The recent recovery of Kirtlands Warbler Dendroica kirtlandii illustrates the potential of active habitat management in securing populations of threatened species. The warblers exacting requirements for breeding habitatstands of young (523 year old) jack pine Pinus banksiana growing on well-drained soilsmean that its breeding range is confined to a small area in the Lower Peninsula region of Michigan, USA. Counts of singing males in 1951 and 1961 totalled 432 and 502 respectively, but this declined to 201 in 1971. A suite of measures was then put in place to stabilise the population. These included control of Brown-headed Cowbird Molothrus ater (a brood parasite of the warbler), annual population censuses and active management of the speciess jack pine habitats. The population remained relatively stable between 1971 and 1987, with suitable habitat regenerating after wildfires or management action apparently offset by losses due to the increasing over-maturity of many older pine stands. However, following further management action and two large wildfires, the amount of suitably aged habitat doubled between 1987 and 1990, and the warbler As a result of intensive habitat management, the population more than tripled between breeding population of Kirtland’s Warbler more 1990 and 2000 in response (see than tripled between 1990 and 2000 figure). By 2000, the population had reached the maximum 1,200 projected carrying capacity within 1,000 its core breeding range (in 800 Michigans Lower Peninsula), with 600 the number of peripheral breeding records (in the Upper Peninsular 400 region and in Wisconsin) 200 increasing over the same period.
Number of singing males
With appropriate action, species can recover
SOURCE Probst et al. (2003) Oryx 37: 365–373.