shows signs of failing. Close guarding has been an important component in
restoration programs for the Kakapo, Chatham Island Black Robin, Californian
Condor, and Echo Parakeet. It has enhanced the productivity of focal pairs (e.g.
Butler and Merton 1992; Jones and Duffy 1993; Jones et al. 1998; Merton et al.
1999; Snyder and Snyder 2000; Elliott et al. 2001).
12.4.2Clutch and brood manipulations
The purposes of clutch and brood manipulations are to increase the productivity
of focal pairs, providing the birds concerned will tolerate the intrusion. In most
species of birds, the number of fertile eggs laid is considerably greater than the
number of young that leave the nest. There are losses during incubation and rear-
ing that can often be minimized by careful management, and the eggs or young
can be harvested without increasing the overall loss.
In some species, if eggs are harvested one at a time or as whole clutches, replace-
ment eggs, or clutches are laid, thereby increasing the number of viable eggs
produced. The harvested eggs can then be hatched in other ways, and the young
reared by hand or fostered in other nests. Brood manipulations increase or
decrease the number of young in the nest, but can also involve cross-fostering,
fostering, or supportive care to the chicks and parents.
Harvesting and rescuing eggs
These techniques have been applied to many species to minimize the loss of
viable eggs. The Whooping Crane Grus americananormally lays two eggs but
only one young usually survives. The “surplus” eggs were harvested for captive
rearing. Of 50 eggs harvested from the wild, 41 (82%) hatched and 23 (56%) of
the chicks were reared to at least 6 months old (Kepler 1978). These were used to
establish a captive population to provide eggs and young for reintroduction.
An important egg harvesting study involved Peregrine Falcons in North America.
The falcons had poor breeding success due to DDE contamination (from the
insecticide DDT) that was causing the females to lay thin-shelled eggs. Most
pairs failed because the incubating adults accidentally smashed the eggs, and this
caused populations to decline. In one study, the hatch rate of thin-shelled eggs
under the wild birds was only 7% (Craig et al. 1988). In a sample of 661 har-
vested eggs, 536 were apparently fertile and alive when harvested, 386 (72%)
hatched, and 356 (92%) chicks were reared to fledging. The majority of these
were released by fostering and hacking (Burnham et al. 1988; Walton and
Thelander 1988). The latter is a procedure that allows young to fly naturally
from an artificial nest-site, to which they can return for food until they have
learned to hunt for themselves about a month later.
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