Environmental Engineering Reference
In-Depth Information
heavy fishing mortality, lack of native gene pools
and complicated political jurisdictions that rarely
work towards a common vision. Meffe (1995) proposes
that a more realistic goal would be rehabilitation, a
movement along the trajectory towards complete
restoration.
Until now, most re-introduction projects involving
amphibians and reptiles have not been very suc-
cessful (Dodd & Seigel 1991), but efforts undertaken
for the natterjack toad (
Bufo calamita
) represent
an interesting exception. The species is endangered
in Britain and has been legally protected since 1975.
This amphibian suffered a major decline during the
first half of the 20th century, due partly to habitat
destruction but mostly to successional changes in its
specialized biotopes and anthropogenic acidification
of breeding sites. Extensive autecological research
over the past 25 years has provided the foundations
for an intensive, 3-year species-recovery programme
funded by statutory nature-conservation organizations.
Management of heath and dune habitats focused on
restoration and maintenance of early stages of serial
succession, initially through physical clearance of
invasive scrub and woodland vegetation, followed by
applying grazing regimes similar to those prevalent
in earlier centuries. In some cases extra breeding
pools were constructed to either increase or stabilize
natterjack toad populations that had become reliant
on one or very few pools at small sites, or to pro-
mote range expansion within large habitat areas. Re-
introductions also had been attempted. At least six out
of 20 re-introductions resulted in the foundation of
expanding new populations, and an additional eight
have shown initial signs of success. Conservation
methods developed for
B. calamita
provided a useful
precedent for long-term conservation of early suc-
cessional habitats and species (Denton
et al.
1997).
(e.g. predation). This has been found, among others, in
whooping cranes (
Grus americana
), hand-reared caper-
caillie (
T. urogallus
), white storks (
Ciconia ciconia
)
and raven (
Corvus corax
). Releasing individuals
straight into the wild (hard release) is not recommended
by Bright and Morris (1994). Most species of birds (and
mammals) rely heavily on individual experience and
learning as juveniles for their survival. They should
be given the opportunity to acquire the necessary
information to enable survival in the wild. Therefore,
soft-release techniques have been developed whereby
the animals are kept in pens or other holding devices
and slowly are made acquainted with their new
environment.
A commonly used soft-release technique for the
introduction of birds of prey is called hacking.
Hacking is the release of free-flying young birds at
a site where food is provided until independence.
Hacking was used in the re-introduction of Montagu's
harrier (
Circus pygargus
; Pomarol 1994). It took place
in an enclosure measuring 3 - 4 m × 2m× 1 m high. The
re-introduced harriers were between 20 and 30 days
of age. After 5 - 8 days the enclosure was opened.
The young birds became independent on average
34 days after their first flight (at 70 days of age). Over
a 5-year period 87 birds were (re-)introduced with a
success rate of 83%. Only three birds had been seen
returning to the area in subsequent years. Hacking
has also been applied very successfully in the many
re-introduction projects of the peregrine falcon
(
Falco peregrinus
). Over the past 25 years more than
1000 birds have been re-introduced in this way in
many parts of the USA.
More than 1670 attempts have been made to estab-
lish several hundred avian species worldwide. Among
them are many raptors. At least six species of owls
and 15 species of diurnal raptors have been established
successfully. Examples of raptors that have been re-
introduced or newly introduced are little owl (
Athene
noctua
) in Britain, eagle owl (
Bubo bubo
) in Sweden
and Germany, goshawk (
A. gentilis
) in Britain, white-
tailed sea eagle (
Haliaeetus albicilla
) in Scotland and
other parts of Europe, bald eagle (
Haliaeetus leuco-
cephalus
) in New York and California, Seychelles
kestrel (
Falco araea
) on Praslin (Seychelles) and the
peregrine falcon (
F. peregrinus
) in the USA, Canada
and Germany. A raptor that almost became extinct is
the Mauritius kestrel (
Falco punctatus
). By 1974, the
7.5.3 Birds
In birds, making use of captive-produced eggs that
are fostered or cross-fostered is a common and viable
re-introduction technique (Derrickson & Carpenter
1983). Sometimes eggs are collected from wild popu-
lations. Fostering has proved to be a much better
technique than the release of hand-reared individuals
as they are much more prone to all sorts of danger
