3.5 Using artificial nests to measure nest success and causes of failure
In recent decades many studies have used artificial nests placed in sites that resemble
the places where real birds put their nests. Frequently, nests are deployedthat
contain eggs from a domesticated bird species or some other readily obtained
type of egg. The artificial nests are then visited at intervals and the fate of the eggs
and the signs left at the nest are recorded as for the real nests of wild birds (see
above). Eggs made from plasticine or modeling clay may be used to aid the iden-
tification of predators from tooth, claw, or bill marks, and cameras that auto-
matically photograph predators can also be used (see Section 3.4). Nest failure
rates can be calculated using the same methods as for real nests. The results are
often interpreted as reflecting differences among years, areas, or habitats in the
risk of egg predation or nest parasitism and the relative importance of different
causes of nest failure of real nests. So many studies of this type have addressed
similar questions that it is now possible to carry out meta-analyses of data from
large numbers of independent studies (Hartley and Hunter 1998).
This approach has several advantages. The most important is that it is easier to
deploy much large numbers of artificial nests than to locate similar numbers of real
nests of many species. This enables powerful tests of hypotheses to be made. The
method also allows some confounding variables, such as nest density and nest site
type, to be manipulated or standardized. However, there are also many disadvan-
tages. Failure rates and causes of failure of artificial nests may not resemble those of
real nests for several reasons. Artificial nest sites may differ from the sites of real nests
in ways that are significant to predators, such as the extent of concealment. Predators
may use different cues, such as observations of parent birds, to find real nests from
those they use to locate artificial nests. Parent birds may be capable of preventing
predation of their nests by attacking or distracting predators, but this does not occur
at artificial nests. Predators may be deterred or attracted by features of the artificial
nests or their eggs that differ from those of real nests and eggs. For example, many
experiments concerned with forest passerine birds in North America have used the
readily available eggs of domesticated Japanese Quail Coturnix japonica, but these
are larger than the eggs of most of the wild species that were the main focus of the
studies (Haskell 1995). Quail eggs were too large for easy consumption by small
rodents, which were important predators of real nests in some areas. Small rodents
were more likely to damage house sparrow Passer domesticuseggs than quail eggs they
encountered (Majer and De Graaf 2000), indicating that the eggs of sparrows or
other small passerines in the experiments would make them more realistic.
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