International Conservation News

Evidence of Continuing Worldwide Declines in Bird Populations: Insights from an International Conference in New Zealand

Over the last 400 years, New able to send representatives, making history of avian extinctions is suffi- Zealand and its surrounding islands this the largest attendance at an ciently well documented since have experienced 11 extinctions of ICBP conference. ICBP itself funded about 1600 to provide an estimate bird species. Prior to that time, the the attendance of 50 delegates, of the modern rate of species loss, a most dramatic and tragic of all New many from developing countries. rate that is substantially in excess of Zealand's avian extinctions was the Themes of conference symposia the background rates characteristic loss of the genus Moa a group com- included birds and tourism, manage- of the early Pleistocene (King prised of as many as 24 species and ment methods for recovery of 1985). In addition, strong circum- ranging in size up to 300 kg. In a threatened birds, conservation of bi- stantial evidence links almost all of land historically without terrestrial ological diversity, and bird conser- the modern extinctions directly or mammals, they filled a niche unique vation problems in the South Pacific. indirectly to the effects of humans. among the world's birds. New Many of the offered papers focused Unfortunately, individual case stud- Zealand's conservationists still face on island ecosystems and applied ies presented in the symposium on many challenges, including continu- their conclusions to insular habitats. conservation problems in the South ing habitat destruction and the in- Oceanic islands support only a small Pacific indicated that the rates of creasing number of introduced percentage of the world's avifauna loss are not declining. Several speak- predators. Today, 17 of the bird spe- but disproportionately account for ers pointed out that unless aggres- cies in this area are threatened en- the vast majority of avian extinct- sive recovery and conservation ef- demics, among them some of the tions. The dynamics of island popu- forts are made within the next world's rarest birds. Having always lations provide useful models for in- decade, the almost complete loss of played a special part in New sular populations of birds on endemic and native bird species is Zealand's culture, birds now sym- fragmented continental land masses. assured on many islands and in many bolize the country's emerging con- Island systems and fragmented con- insular systems. servation movement, and despite its tinental landscapes have similar Varying with location, ecosystem problems, New Zealand is becoming characteristics that affect popula- type, and species, the major causes a world leader in biological conser- tions, including "island" size and of avian endangerment and extinct- vation. shape, degree of isolation, sensitivity tion are loss of habitat, predation, With this history, New Zealand to a species' dispersal capabilities overhunting, competition, and dis- provided a poignant setting for last between islands, and the effects of ease (King 1985). For example, the fall's international conference on small population sizes. The study of role of introduced predators, partic- bird conservation sponsored by the the dynamics of island populations ularly rats (Rattus spp. ), in the de- International Council for Bird Preser- thus provides insights into the ef- mise of island populations of vation (ICBP). On 21 November fects of insularization of continental ground-nesting island birds is partic- 1990, 380 conservationists from 56 avifaunas. ularly well documented (Atkinson nations- converged on Hamilton, However, given the degree of 1985) and continues to be a major N.Z., for ICBP's 20th World Confer- threat to island biotas, it is unclear source of loss of island species. One ence. Thanks to generous grants for how much longer islands will of the most tragic examples of pred- from a number of foundations, many serve as natural laboratories for the ator-induced endangerment and ex- countries for the first time were study of the extinction process. The tinction is the precipitous decline of

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Conservation Biology Volume 5, No. 2, June 1991 142 International Conservation New

Guam's native forest birds coinci- in the wild. According to historical natural levels, a consequence of in- dent with the introduction and records, however, the bird was rare direct degradation or direct destruc- range expansion of the brown tree upon its discovery in 1819, probably tion by humans. The following ex- snake (Boiga irregularis) (Savidge due to its dependence upon riverine amples, drawn from conservation 1987). Of 11 native forest birds ex- habitat, which even by 1819 had resolutions and action items of the tant at the time of the snake's intro- been cleared and degraded by graz- ICBP, emphasize the significance of duction, 7 are now extinct and the ing. As in these cases, the proximate species endangerment due to habi- remaining 4 are critically endan- factor that delivers the final blow to tat loss. These examples demon- gered (Haig et al. 1990). Island spe- a species is often quite distinct from strate that habitat loss is a threat to cies not previously exposed to the the ultimate factors that lead to the both temperate and tropical areas, selective pressures of predation lack species' endangerment. affects populations on both oceanic predator avoidance behaviors and The slender-billed curlew (Nume- islands and continental mainlands, is remain extremely vulnerable to in- nius tenuirostris) also suffers from promoted by both Third World and troduced predators, including hu- the synergistic effects of several ad- industrialized nations, and is often mans. The negative effects of human verse factors acting simultaneously. most acute in areas of high avian en- predation are dramatically illus- The proximate threat to the species' demism, that is, regions that histori- trated in the eastern part of the In- persistence is poaching. The species' cally have served as the key source donesian archipelago where recent recovery, however, will require not areas of avian evolution and adaptive declines in some seabird popula- only the control of illegal hunting radiation. tions can be attributed directly to but also protection of breeding, win- The Danube Delta in Romania, human exploitation of birds and tering, and migration habitat one of Europe's most significant eggs (de Korte 1989). throughout Europe and Asia. Many wetlands, supports some of the larg- Most extinctions of species can- stopover areas critical to the cur- est populations of bird species that not be attributed to a single factor, lew's successful migration are only a are generally widespread across Eu- but are a consequence of several fac- fraction of their former size. Habitat rope. Over 160 bird species breed in tors working simultaneously, or se- preserves on the breeding grounds the Danube Delta, among them pop- quentially. For example, Hawaiian in Siberia, wintering sites in Iraq and ulations of pelicans, herons, ibises, bird populations have been sub- Iran, and stopover habitats such as and terns. Direct threats to the Delta jected to waves of extinction- the steppe in Hungary and Yugosla- include reclamation and conversion causing impacts beginning with hab- via and wetlands in Romania, of the wetland to agricultural land. itat destruction, introduced Greece, and Italy are all key compo- In addition, river channelization, predators, and hunting by Polyne- nents of a successful conservation dam construction, pollution, and un- sians prior to European settlement strategy. The conservation problems regulated commodity exploitation of the islands. In the early 1990s, facing the slender-billed curlew il- have degraded the quality of the re- avian malaria was introduced to the lustrate the complexity of conserv- maining habitat. Fortunately, the archipelago. The extinction of many ing species that are long-distance Delta has received at least a tempo- species since the turn of the century migrants and require disparate, geo- rary reprieve; recent presidential de- may have been proximally caused graphically separate habitats for crees have halted for one year all by the malaria epidemic (van Riper breeding, migration, and wintering. agricultural and hydrological devel- et al. 1986 ), but the ultimate histor- Effective conservation requires the opment and have designated the ical impacts on Hawaiian popula- cooperation of many nations with Danube Delta as a Biosphere Re- tions may have weakened them to vastly differing levels of concern for serve. the point at which one more fac- species conservation. Prior to their discovery by the tor-in this case disease--could Though threats to a species often Maoris in the fourteenth century, cause extinction. Several critically involve a complex of factors, the the Chatham Islands, 800 km east of endangered species, for which con- most pervasive and encompassing New Zealand, had about 70 bird spe- servation resolutions were devel- threat to birds and other taxa is loss cies and subspecies. When the is- oped at the ICBP meeting, similarly of habitat. Of course, the amount lands were colonized by Europeans suffer from multifactorial threats. and distribution of suitable habitat in the early nineteenth century, For example, Spix's macaw (Cy- changes as a result of natural pro- there remained only 48 species and anopsitta spixii), a parrot that oc- cesses such as succession or large- subspecies, 20 of which are en- cupies riparian areas in the arid in- scale natural disturbance events. demic. Since that time four species terior of northeast Brazil, has been Many threatened bird species, how- have gone extinct and eight species severely exploited by trappers; by ever, are currently experiencing are currently endangered. Most of 1987 only three birds were known rates of habitat loss far above these extinctions can be attributed

Conservation Biology Volume 5, No. 2, June 1991 International Conservation News 143

to large-scale deforestation, hunting shared vulnerability to demographic mously adopted at the New Zealand pressure, and introduced rats, cats, and environmental uncertainty is meeting. opossums, and livestock. Pressures clear. from continuing deforestation and The weight of current evidence is Barry R Noon predation have restricted many spe- sufficient to compel changes in the U.S. Forest Service Redwood Sciences Laboratory cies to offshore island populations management of habitats threatened 1700 Bayview Drive and continue to threaten critically by reduction and fragmentation. Arcata, CA 95521, USA. endangered species. This level of certainty is justified The Atlantic Forest of southeast- even though most descriptions of Kimberley Young ern Brazil, the third largest distinct extinctions are little more than an- International Council for Bird Preservation biogeographic zone within Brazil, ecdotal accounts of species loss. The c/o World Wildlife Fund-U.S. 1250 24th Street, N.W. originally occupied about 1,000,000 former occurrence of a species on an Washington, D.C. 20037, U.S.A. 2 km . The area is characterized by an island, for example, is usually extremely high level of avian ende- based on a qualitative historical ac- Literature Cited mism: 214 of the 940 species of bird count or, at best, fossil remains. The recorded in the forest are endemic dynamics of the process itself are Atkinson, I. A. E. 1985. The spread of and 80% of these are confined to the seldom documented, nor are the key commensal species of Rattus to oceanic Atlantic Forest. In 1985 the region factors that led to the loss of a spe- islands and their effects on island avifau- held 43% of Brazil's human popula- cies known with certainty. The lack nas. Pages 35-81 in P. J. Moor, editor. tion and the extent of forested land of documented examples is not sur- Conservation of island birds: case stud- had declined to about 10% of its prising given that the extinction ies for the management of threatened is- original area. The costs to avian bio- process can be slow: Unavoidably, land species. ICBP Technical Publication diversity, measured by the associa- extinction "experiments" seldom No. 3. tion between rising human popula- lend themselves to the rigor of sta- tion and declining forest, have been tistical inference if for no other rea- de Korte, J. 1989. Threats to Indonesian extensive. Of the world's 1,029 son than that they cannot be repli- seabird colonies. Conservation Biology threatened bird species, 121 are cated. Those who attempt to dismiss 3:336-337. found in Brazil. Of these 121 spe- the weight of circumstantial evi- cies, 54 occur in the Atlantic Forest dence and ignore the power of in- Haig, S. M., J. D. Ballou, and S. R Derrick- and 36 are confined to that area. ductive inference would assert that son. 1990. Management options for pre- Nearly all of these species are threat- many more "experiments" need to serving genetic diversity: reintroduction ened by habitat loss and fragmenta- be conducted before a cause-effect of Guam Rails to the wild. Conservation tion. relationship between human activi- Biology 4:290-300, 464. The forests of Vietnam are ties and species extinction becomes thought to contain the highest diver- unclear. As scientists we acknowl- King, W. B. 1985. Island birds: will the sity of bird species in Indochina. Yet edge that individual case studies are future repeat the past? Pages 3-15 in P. J. many species are severely threat- seldom, by themselves, compelling; Moor, editor. Conservation of island ened because they exist as small many possible explanations exist for birds: case studies for the management populations isolated by habitat de- the observed outcome. When many of threatened island species. ICBP Tech- struction resulting from the Vietnam case studies suggest similar cause- nical Publication No. 3. wars and by continued deforestation effect relationships, however, their due to logging, fuelwood cutting, collective evidence can support Savidge, J. A. 1987. Extinction of an is- and agriculture. The Vietnamese strong inference. Despite the lack of land forest avifauna by an introduced government has created a protected controlled experimental studies of snake. Ecology 68:660-668. area system, but many of the re- species declines and losses, the col- serves are too small or too isolated lective weight of island case studies van Riper, C., III., S. G. van Riper, M. L to support viable populations of argues strongly that no additional Goff, and M. Laird. 1986. The epizooti- most endangered birds. Meanwhile, replications are needed. Current ev- ology and ecological significance of ma- options to increase the size and idence calls for the immediate im- laria in Hawaiian avifauna. Ecological number of reserves are quickly be- plementation of aggressive interven- Monographs 56:327-344. ing lost as deforestation continues tion, management, and restoration unabated in the surrounding land- policies. This perspective was scape. The parallel between popula- clearly demonstrated by the number tions on such fragmented mainland of resolutions encouraging aggres- reserves and oceanic islands in their sive conservation action unani-

Conservation Biology Volume 5, No. 2, June 1991