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Mounting a birdhouse on a metal pole and applying
grease to the pole after eggs are laid prevents almost all predators form
reaching the birdhouse.
But, Blue Jays, Starlings, Magpies, Crows and other
larger birds that eat or destroy eggs and young songbirds can easily fly
to the birdhouse, stick their head into the nest and take the eggs and
young.
There are three birdhouse design features and one
monitoring procedure that reduces this risk.
First, the entrance hole should be round with a
diameter of no more than an inch and a half or inch and nine
sixteenths. Any larger and European Starlings, now one of the most
common birds in the United States and an one of the worst threats to birds
that nest in birdhouses, can easily enter the birdhouse and raid the nest.
Second, the distance from the hole to the floor
should be between six and a half and seven and a half inches.
Third, the thickness of the front of the birdhouse
where the entrance hole is should between an inch and a half and two
inches. This extra thickness can be achieved by attaching an extra
square block of wood at the location where the hole is to be
drilled. This block of wood is commonly known as the wooden block
predator guard.
Many times a bluebird will use so much nest material
that the top of the nest is very near the entrance hole. In these
cases the eggs and tiny chicks are easy prey for a predator bird that can
stick its head into the birdhouse and pierce the eggs or chicks with its
long bill. This risk can be greatly reduced by removing nest
material from the bottom of the nest until the eggs are only an inch or so
from the bottom. To make sure the nest is not abandoned by the
bluebirds, this procedure should only be performed after all eggs have
been laid and incubation begun. This procedure should not be
performed after the eggs hatch because the tiny birds can be injured when
manipulating the nest material. |