pairs. Of ten pairs whose first clutch was removed, six relayed; and following
removal of these second clutches, three pairs went on to lay a third time in the one
season. The condors were retained to establish the captive-breeding program for
the species (Snyder and Hamber 1985; Snyder 1986; Toone and Wallace 1994;
Snyder and Snyder 2000).
Double clutching of wild Peregrine Falcons became routine in the Western
United States (see Harvesting and rescuing eggs) (e.g. Burnham et al. 1988, Walton
and Thelander 1988). The clutch was typically removed 7–10 days after comple-
tion. The delay in removal was to allow some natural incubation, which increased
the subsequent hatchability in incubators, compared to eggs in incubators
throughout. In one sample of 13 removed first clutches, all pairs laid a second
clutch, usually after about 12 days. Second clutches were sometimes smaller and
averaged 3.2 eggs, compared to 3.5 eggs in first clutches (Craig et al. 1988).
Double clutching was tried on Echo Parakeets, but with poor success. First
clutches were removed, or lost, from wild pairs on 18 occasions, and in twelve
(67%) of these a second clutch was laid. The second clutch was started 19–21 days
(once about 30 days) after the loss of the first clutch. It was difficult to predict in
Echo Parakeets if a pair would renest, and repeat nesting attempts were not as
successful as first ones. Only 23% of eggs from second clutches resulted in
fledged young ( Jones and Duffy 1993; Jones et al. 1998). In view of this poor
success, double clutching was stopped.
Many species respond to loss of a clutch by moving to another nest-site, so
clutch removal has been used to move Peregrine Falcons from unsuitable nest-sites
to secure ones (Craig et al. 1988) and to move Mauritius Kestrels from cavities
that were accessible to predators to predator-proof nest-boxes.
Because egg quality often declines in replacement clutches, there are tradeoffs
in management that have to be considered. A protocol for the harvesting of eggs
from wild pairs of Mauritius Kestrels was developed, in which no pair was made
to lay more than one extra clutch in a season. Harvested eggs of many species of
wild birds have a better hatchability in artificial incubators if they have received
some natural incubation, yet the birds recycle more readily if the eggs are
harvested soon after the first clutch has been laid. In Mauritius Kestrels, the eggs
were harvested about 5–7 days after clutch completion. Following the removal of
the clutch, Mauritius Kestrels would usually move nest-site, so alternative nest-
boxes were provided. First time breeders were left with their first clutch and not
encouraged to lay additional eggs. It was considered important that young birds
should rear young if they were to become good breeders in future years ( Jones
et al. 1991). Similar protocols have been applied to Peregrine Falcons (Walton
and Thelander 1988).
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