Environmental Engineering Reference
In-Depth Information
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
promote range expansion within large habitat areas.
At least six out of 20 experimental reintroductions
have resulted in the foundation of expanding new
populations, and an additional eight have shown initial
signs of success (Denton
et al
. 1997 ).
Translocations of fi sh seem to be more succesful
than those of amphibians with the natterjack toad as
an exception.
cessfully in the many reintroduction projects of the
peregrine falcon (
Falco peregrinus
). Over the past 25
years, more than 1000 birds have been reintroduced
in this way in many parts of the United States.
Many attempts have been made to establish 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 suc-
cessfully. Examples of raptors that have been reintro-
duced or newly introduced are the little owl (
Athene
noctua
) in Britain, eagle owl (
Bubo bubo
) in Sweden and
Germany, goshawk (
Accipiter gentilis
) in Britain, white-
tailed sea eagle (
Haliaeetus albicilla
) in Scotland and
other parts of Europe, bald eagle (
Haliaeetus leucocepha-
lus
) in New York and California, Seychelles kestrel
(
Falco araea
) on Praslin (Seychelles), and peregrine
falcon (
F. peregrinus
) in the United States, Canada and
Germany. A raptor that almost became extinct is the
Mauritius kestrel (
Falco punctatus
). As a result of
habitat loss and pesticide contamination, by 1974 only
four birds were known to exist in the wild, including
one breeding pair. Then, in 1973, a conservation
project was begun, using techniques such as captive
breeding, supplemental feeding of wild birds, provision
of nestboxes, hand rearing and release of captive-bred
and captive-reared birds by hacking, fostering and
predator control (Jones
et al
. 1995). A total of 331
kestrels were released in the 10 years up to the end of
the 1993-1994 breeding season; one-third of these
were captive bred and the rest were derived from eggs
harvested from the wild. By the 1993-1994 season, an
estimated 56-68 pairs had established territories in the
wild with a postbreeding population, including fl oating
birds and independent young, of 222-286. Since the
pesticides responsible for their decline are no longer
used, the number of Mauritius kestrels should con-
tinue to rise through natural recruitment. The distri-
bution of suitable habitat suggests that an eventual
population of 500-600 kestrels on Mauritius is possi-
ble. Due to its outstanding success, the release pro-
gramme for the Mauritius kestrel ended after the
1993-1994 breeding season (Jones
et al
. 1995 ).
8.5.3
Birds
In birds, making use of captive-produced eggs that are
being hatched by common species like chickens is a
common and viable reintroduction technique (Der-
rickson & Carpenter 1983). Sometimes eggs are col-
lected from wild populations. 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 (e.g. predation). This has been found,
among others, in whooping crane (
Grus americana
),
hand - reared capercaillie (
Tetrao urogallus
), white storks
(
Ciconia ciconia
) and common raven (
Corvus corax
).
Releasing individuals straight into the wild - known as
hard - release
- is not recommended by Bright and Morris
(1994). Most species of birds (and mammals) rely
heavily on individual experience and learning as juve-
niles for their survival. They should be given the oppor-
tunity 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
, that is,
the release of free-fl ying young birds at a site where
food is provided until independence. Hacking was used
in the reintroduction of Montagu's harrier (
Circus pyg-
argus
; Pomarol 1994). It took place in an enclosure
measuring 3 - 4 m × 2 m × 1 m high. The reintroduced
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 fi rst
fl ight (at 70 days of age). Over a 5-year period, 87 birds
were reintroduced with a success rate of 83%. Only
three birds had been seen returning to the area in sub-
sequent years. Hacking has also been applied very suc-
8.5.4
Mammals
As with birds, mammals can be taken from wild
source populations or from captive breeding stock.
Catching animals from the wild can be a costly and
time-consuming operation, and is not without risk.
