The Cranes IUCN

1.6 Threats
The world's cranes face a wide array of existing and potential
threats. The threats and their approximate levels of impact
on the various crane species are summarized in Table 1.3.
Particular threats for each species are discussed within the
species accounts in Section 2. Anthropogenic threats to cranes
can be divided into several categories: habitat loss and degradation;
direct exploitation; poisoning; and other anthropogenic
threats.
1.6.1 Habitat Loss and Degradation
Habitat loss and degradation is the most important class of
threats to the world's cranes (Archibald et al. 1981, Harris
1994a). Declines in habitat availability and quality affect the
distribution, movement, and breeding success of cranes, and
involve all habitat types—breeding grounds, migration
stopover points and staging areas, wintering grounds, resident
habitats, and roosting areas. Major forms of habitat loss and
degradation affecting cranes include the following:
Conversion of wetlands
Conversion of wetlands for agricultural and non-agricultural
purposes (including urban, commercial, and recreational
development, oil exploration, and road construction) is the
most significant factor affecting cranes and their habitats
around the world (see Harris 1994a, Hussain 1994 Zhang
1994),. The process of converting wetlands usually involves
extensive clearing of natural vegetation, draining and other
alterations of hydrological processes, burning, cultivation, and
other activities that render former crane habitats unsuitable for
nesting, feeding, roosting, and stopping during migration. All
of the wetland-dependent crane species have been affected by
this process to a greater or lesser degree.
Over-exploitation of wetland resources
Cranes and people have long coexisted successfully in
many wetland areas, but increasing pressures related to human
population growth and economic constraints have in some
areas overtaxed wetland ecosystems and the resources they
provide. Overexploitation of the plant, animal (especially
fish), and water resources of these wetlands can have negative
impacts upon cranes and other species (e.g., Ma and Su
1991,Wang Q. 1991, Harris 1992a, Su 1992). This problem is
perhaps greatest in areas of Africa and Asia where population
pressures are greatest and wetland resources are used to meet
expanding subsistence needs.
Conversion of grasslands
Agricultural expansion into grasslands has also appropriated
crane breeding and foraging habitat, especially in sub-
Saharan Africa, parts of South Africa, the steppe regions of
Eurasia, and savannas and prairies in North America (Vernon
et al. 1992, Allan and Nuttall 1995, Winter et al. 1995,Allen 1952).
19
Changes in agricultural land use
In areas where cranes have adapted to feeding and breeding
in traditional agricultural lands, changes in the choice of
crops, fallow and rotation schedules, cropping patterns, field
preparation, and cultivation and harvesting practices can have
subtle but important effects (e.g., Bishop 1991, Khachar et al.
1991, Mafabi 1991, Winter et al. 1995).
Other agricultural impacts
In many landscapes, agricultural practices in upland areas
have brought about increased rates of soil erosion. The resulting
sediment loads alter the hydrological processes and vegetation
in downslope wetlands. This has had direct impacts on crane
habitat in Japan, China, Australia, and other areas (Archibald
1987, Li F. and Li M. 1991, A. Haffenden pers. comm.).
Intensified livestock grazing has resulted in the degradation of
crane habitat through disturbance, alterations in wetland hydrology,
and trampling of wetland vegetation (including crane nests
and cover vegetation) (e.g., Duc 1991, Gole 1991a, Urban and
Gichuki 1991, Mustafa and Durbunde 1992). Increased use of
pesticides and fertilizers in agricultural systems impacts cranes
directly through exposure and ingestion and indirectly through
eutrophication and contamination of wetlands, accumulation in
food sources, and changes in the trophic structure of ecosystems
(Gole 1989b, 1991b; Kawamura 1991; Muralidharan 1992).
Dams and water diversion
Construction of dams and irrigation systems has profoundly
altered the hydrological regimes and stream channel characteristics
of river systems and associated wetlands critical to
many crane species. Dam construction and water diversion has
already affected large river and wetland systems such as the
Senegal, Zambezi, Lake Chad, Danube, and Platte, as well as
many smaller streams and wetlands. Other major river systems
that are critically important for cranes—including the
Mekong, Yangtze, and Amur Rivers, the Okavango system,
Agricultural and industrial development threaten wetlands in Vietnam
ICF