Action: Provide supplementary food for cranes to increase adult survival
Key messagesRead our guidance on Key messages before continuing
A before-and-after study from Japan and a global literature review found that local crane populations increased after the provision of supplementary food.
Well-fed animals are likely to be in better physical condition than those with too little food: having greater muscle mass and larger fat supplies to help them survive lean periods. However, it is worth noting that species that forage in groups can have dominance hierarchies, which alter the relationship between weight and fitness. For example Gentle and Gosler (2001) found that, amongst great tits Parus major in Oxfordshire, England, more dominant birds had a lower mass than subdominants, particularly when perceived predation risk was high. Birds with lower masses are better able to take off and therefore escape predators than heavier birds (Krams 2002). However, because of their dominance, they were able to usurp other birds from food resources when hungry. Care should therefore be taken when interpreting results which do not directly examine survival.
Krams, I. (2002) Mass-dependent take-off ability in wintering great tits (Parus major): comparison of top-ranked adult males and subordinate juvenile females. Behavioral Ecology and Sociobiology, 51, 345–349.
Gentle, L.K. & Gosler, A.G. (2001) Fat reserves and perceived predation risk in the great tit, Parus major. Proceedings of the Royal Society of London. Series B: Biological Sciences, 268, 487.
Supporting evidence from individual studies
A before-and-after study of red-crowned cranes Grus japonensis in Hokkaido, Japan, in the mid-20th century (Masatomi 1991) found that a local population increased from 42 individuals in 1952-4 to 161 in 1960-4. This followed the establishment of an artificial feeding station in 1952, and the author attributes the population rise to supplementary food reducing winter mortality, although no data is provided for the use of the feeding station, any reduction in starvation or increase in reproductive productivity. No details are provided about the supplementary food provided.
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.
- Masatomi H. (1991) Population dynamics of red-crowned cranes in Hokkaido since the 1950s. Proceedings of the 1987 International Crane Workshop International Crane Foundation, Baraboo, Wisconsin, USA, 297-299.
- Davis C. (1998) A review of the success of major crane conservation techniques. Bird Conservation International, 8, 19-29