become extirpated (IUCN 1998), but can also include the addition of individuals
to an existing population. This latter category of reintroductions is often treated
separately as re-enforcement or supplementation (IUCN 1998), but since both
types of reintroduction are often used in the same project, they are here treated
together.
Reintroductions have received a great deal of attention due to their high profile
nature (Fyfe 1978; Cade 2000). The reintroduction of some species works well
(birds of prey), and others have proven problematic (parrots, hornbills, and some
passerines). Successes are becoming more frequent, as we learn more about the
needs of different species. There are several different release techniques, of which
fostering and cross-fostering of eggs and young have already been described. Other
release processes can be divided into hard or soft releases. The hard release (also
termed abrupt release) is when the bird is released without any preliminary condi-
tioning to the area and is not given any support thereafter, on the assumption that
it will be able to look after itself. Many early reintroductions were of this type and
were characterized by a high failure rate. As a rule, hard releases are best avoided.
In soft release (also called gentle release), the birds are habituated to the area
before release and are provided with some form of support during the release
process. Usually the birds are provisioned after release with food and water, so
that they can become independent of human care gradually. Soft releases are
more successful than hard-releases. For example, post release survival to 1 year
was 12% of 51 Sandhill Cranes that were hard-released, and 68% of 238 cranes
that were soft-released (Nagendran et al. 1996).
The process of a soft release falls into three stages: (1) pre-release training and
conditioning; (2) the release process; and (3) post-release support. Birds intended
for release have to be correctly socialized, with due care taken to ensure that the
stimuli during the early learning stages are appropriate. For most releases, parent
reared, or foster raised birds are to be desired because they will have experienced
normal imprinting and socialization. If hand-raised birds are being used, it is
important that they are raised with siblings to ensure socialization with con-
specifics or, if they are being raised alone, that they are fed with the aid of a pup-
pet that mimics the adult so that the young birds imprint upon an appropriate
image (Wallace 2000). Puppet rearing has been used with Californian Condors,
and Takahe Porphyrio mantelli. For cranes, the rearer wears a full body crane suit.
Attention also needs to be given to early learning of nest-site characteristics, and
all individuals should be provided with opportunities to develop physical and
survival skills (Wallace 2000).
Birds of prey are usually released using a soft release technique called “hacking”
(Sherrod et al. 1981). The birds are placed in an artificial nest-site once they are
homeothermic and are old enough to feed themselves from provisioned food.
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