Individual study: Soft-release of captive-bred greater sandhill cranes Grus canadensis tabida is more successful than cross-fostering in Florida, USA
Nesbitt S.A. & Carpenter J.W. (1993) Survival and Movements of Greater Sandhill Cranes Experimentally Released in Florida. The Journal of Wildlife Management, 57, 673-679
This study is summarised as evidence for the intervention(s) shown on the right. The icon shows which synopsis it is relevant to.
Foster eggs or chicks of cranes with wild non-conspecifics (cross-fostering)
As part of the planning for a whooping crane Grus americana reintroduction programme, a replicated study in Florida, USA, in 1982-7 (Nesbitt & Carpenter 1993) found that 22% of 23 wild Florida sandhill crane G. canadensis pratensis pairs successfully fledged chicks from captive-laid greater sandhill crane G. c. tabida eggs fostered in their nests. A further 35% hatched at least one egg but failed to fledge any chicks, 26% began incubation but then abandoned the substituted eggs and 17% immediately abandoned the eggs. Overall, survival of 34 cross-fostered eggs was 39% (from hatching to leaving the territory), lower than the 56% survival of captive-bred and released cranes, discussed in ‘Release captive-bred individuals’. The eggs came from a combination of wild birds in Idaho, USA, and captive birds from Florida. Greater sandhill cranes are migratory, whilst Florida sandhill cranes are not. Migratory movements of fostered birds were larger than a control group of Florida sandhill cranes, but not significantly so.
Release captive-bred individuals into the wild to restore or augment wild populations of cranes
A replicated study as part of the planning for a whooping crane Grus americana reintroduction programme, a study in Florida, USA, in 1986-7 (Nesbitt & Carpenter 1993) found that greater sandhill cranes Grus canadensis tabida released as sub-adults in a ‘soft release’ programme had higher survival than birds fostered to Florida sandhill cranes G. c. pratensis (56% of 27 birds surviving for one year vs. 39% survival for 34 fostered birds, discussed in ‘Foster eggs or chicks with wild non-conspecifics (cross-fostering)’). The nine to ten month-old cranes were prevented from flying and kept in an open-topped 1.5 ha enclosure for four to six weeks until they were released. Food was provided until the birds no longer returned to the enclosure. Greater sandhill cranes are migratory, whilst Florida sandhill cranes are not. Migratory movements of released birds were larger than a control group of Florida sandhill cranes, but not significantly so.