Individual study: A review of the success of supplementary feeding of cranes
Davis C. (1998) A review of the success of major crane conservation techniques. Bird Conservation International, 8, 19-29
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Legally protect habitats
A 1998 literature review (Davis 1998) found that 25,500-31,800 cranes (Gruidae) of seven species used 32 nature reserves, established mainly for crane conservation, in China in 1994. This review is also discussed in ‘Use education programmes and local engagement to help reduce pressures on species’, ‘Use legislative regulation to protect wild populations’, ‘Mark power lines to reduce incidental mortality’, ‘Provide supplementary food to increase adult survival’ and ‘Release captive-bred individuals’.
Provide supplementary food for cranes to increase adult survival
A 1998 literature review (Davis 1998) found that supplementary feeding of cranes appeared to increase local populations five, and possibly six species of crane in five sites across the world. These were red-crowned cranes Grus japonensis in Hokkaido, Japan (Masatomi 1991); hooded cranes G. monachus and white-naped cranes G. vipio wintering at Izumi, Japan; common cranes G. grus at Lake Hornborga, Sweden; and demoiselle cranes Anthropoides virgo at Khichan in India. It is also possible that winter feeding of whooping cranes G. americana in 1993-4 may have encouraged population growth. The author recommends that supplementary feeding is viewed as a potential short-term practice, but that the risks from spreading disease and increased human disturbances may make it unsuitable as a long-term strategy.
Use education programmes and local engagement to help reduce persecution or exploitation of species
A 1998 literature review of crane Grus spp. conservation (Davis 1998) describes how whooping cranes G. americana continued to decline in the USA following legal protection, until intensive public education programmes. Before education, fewer than half the recorded whooping crane mortalities were due to natural causes, but between 1968 and 1998, only four whooping cranes are known to have been shot. This review is discussed in more detail in ‘Habitat protection’, ‘Use legislative regulation to protect wild populations’, ‘Mark power lines to reduce incidental mortality’, ‘Provide supplementary food to increase adult survival’ and ‘Release captive-bred individuals’.
Use legislative regulation to protect wild populations
A 1998 literature review of crane Grus spp. conservation (Davis 1998) described how two of four case studies found a positive response of crane populations to legal protection, with one showing partial success and the final study finding that legal protection had no impact. A small population of red-crowned cranes G. japonensis remained stable and increased slightly (from 20 to 35 birds between 1925-52) following legal protection at Kushiro Marsh, Hokkaido, Japan; whilst the American population of migratory sandhill cranes G. canadensis increased dramatically following a ban on hunting. Whooping cranes G. americana continued to decline following protection in 1916, but after public education, only four birds are thought to have been shot (see ‘Use education programmes and local engagement to help reduce pressures on species’). The central Asian population of Siberian cranes G. leucogeranus continued to decline in India, from 200 in 1964-5 to three in 1996-7 despite protection in flyways in Pakistan. This study is also discussed in ‘Habitat protection’, ‘Use education programmes and local engagement to help reduce pressures on species’, ‘Mark power lines to reduce incidental mortality’, ‘Provide supplementary food to increase adult survival’ and ‘Release captive-bred individuals’.
Release captive-bred individuals into the wild to restore or augment wild populations of cranes
A 1998 review (Davis 1998) found that crane Grus spp. reintroduction programmes have had mixed success, with reintroductions of migratory species generally failing when birds were not released into existing flocks. Reintroductions of Siberian cranes G. leucogeranus has not increased wild flock size, with no reintroduced birds being seen after migration and high mortality during rearing, high poaching levels and few wild birds to guide migration. Releases of semi-wild red-crowned cranes G. japonensis and white-naped cranes G. vipio in southeast Russia found that four of ten released birds migrated successfully, and at least two pairs nested, one successfully. At least 84% of 38 greater sandhill cranes G. canadensis tabida survived for a year after release in Michigan, USA, 74% returned after migration and four males nested. Non-migratory releases generally had higher success: first-year survival of non-migratory whooping cranes G. americana has increased from approximately 34% (1993-4) to 71% (1996), although the population remains very small and may rely on continued releases. Captive-reared Mississippi sandhill cranes G. c. pulla had an overall first-year survival of 70%, an adult survival over 91% following release and in 1992 represented 80% of the wild population. In 1996 there were 13 nesting pairs (the most recorded), with 60% of known pairs having at least one captive-reared individuals. The population, however, remains dependent on releases. The author argues that post-release monitoring is vital to identify causes of mortality.
Mark power lines to reduce incidental bird mortality
A literature review (Davis 1998) found three studies, all of which show a reduction in crane Grus spp. mortality, following the marking of power lines. Morkill & Anderson (1991) and Brown & Drewien (1995) are discussed elsewhere. The third study found that marking, burying or removing power lines in Japan reduced the percentage of red-crowned crane Grus japonicus mortalities attributed to power line collisions from 70.9% (1970-4) to 26.8% (1980-4). The rate of population increase rose from 5.9% (1970-4) to 18.9% (1980-4). There was also an increase in the number of breeding pairs and the percentage of juveniles in the population.