Background
Western bluebirds and many other cavity-nesting birds are declining in
population and are having difficulty breeding successfully because of
changes in climate and because of increasing interference by non-native
species and predators that reduce their success in cavity nests. For
these reasons, groups such as the California Bluebird Recovery Program
(CBRP) have formed to help cavity-nesting birds recover their numbers
and to stabilize or increase their populations. The photo to the right
shows a male western bluebird near Borges Ranch at the beginning of the
nesting season. |
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Walnut Creek and other communities in central Contra Costa County,
volunteers from CBRP, the Walnut Creek Open Space Foundation and the
Mt. Diablo Audubon Society are working together to install and monitor
cavity nest boxes. These boxes have openings small enough to
exclude some predators while admitting the birds that will benefit from
the nesting sites. The female bluebird shown here has not decided yet
whether to nest in this box in Shell Ridge Open Space. |
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Building a Bluebird Trail
Cavity nest boxes are placed along a route in an open space area. Plans
for the boxes allow the construction of two cavity nest boxes from a
single 1” x 6” x 5’ fence board. The
remains of people’s yard fences can often be recycled when
they rebuild. As an example, we will show the construction of a trail
in the northern section of Lime Ridge North Open Space for the 2009
nesting season. Brian Murphy has devised a hand-truck carrier to hold
eleven nest boxes and tools. |
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nest box is attached to the tree with either nails or deck screws.
Don’t worry, only a very small portion of the bark on the tree
is affected. The box is positioned high enough that cattle or deer
cannot knock into it but low enough for volunteers to see into when
they check for nesting progress. The center of the box is about five
feet above the ground. Boxes are mounted on oak trees that provide at
least partial shade during hot days |
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After
the box is mounted, we record data including the date of installation,
the location and orientation and the distance from the nearest
neighboring nest box. Western bluebirds will not build nests close to
those of other bluebirds. Typically we install nest boxes more than 100
feet away from the nearest neighbor and make sure that birds cannot see
the nearest neighboring box. Boxes place on trees at the edge of
woodlands and near meadows seem to be most successful for bluebird
nesting.
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Monitoring Nest Boxes
Volunteers adopt a particular bluebird trail and monitor it. Beginning
in March, they start visiting the boxes on their bluebird trail and
look for signs of nesting. They carry tools including a screwdriver to
open the door of each box and a tool such as a paint scraper or putty
knife to clean out boxes. It’s a good idea to carry water,
binoculars and a camera as well. Approaching the box we observe whether
cavity nesting birds are in the area. We open the side door and look
for signs of nesting. |
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Nest Types We
Typically Observe
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Oak Titmouse Nest
Some birds leave feathers or small amounts of nesting material such as
twigs of grass to mark the box before they start the nest.
Shown here is an oak titmouse nest made of fresh moss and grass. Note
that the moss on the tree trunk next to nest box. The nest contains
three eggs already but eventually had seven eggs laid over several
days. The titmouse is the earliest nester in the Walnut Creek cavity
nest boxes. Titmice are very protective of their nests! |
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Western Bluebird Nest
Bluebird nests are first observed shortly after those for the titmouse
and bluebirds may nest more than once in a season. The eggs are a
beautiful blue color. We typically find between two and five eggs in a
nest. It is typical for bluebirds to leave a bright blue feather in a
nest box before beginning nest construction. They usually build their
nests entirely from grass, unlike most other cavity nesters. |
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Ash-throated Flycatcher Nest
This bird is very reclusive; you have to be very observant to notice
it. One is more likely to find a nest for these birds in the woods.
Here we see the female on a new nest made with animal fur and moss. She
chatters at me as I look into the box as though demanding that I leave.
Hair from cattle is often observed in these nests. The eggs, shown in
the nest photo are very distinctively striped and easy to distinguish
from those of other species. |
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Violet-green Swallow Nest
These nests are usually made with a grass base and a layer of feathers
of birds from other species. There are six local swallow species; tree
swallows and violet-green swallows sometimes use our boxes for their
nests. Note the pale-pink unspotted eggs. The swallows are very visible
around the nest during construction and throughout the nesting process. |
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White-breasted Nuthatch Nest
These are birds that you often see clutching sideways or upside down on
oak trees as shown in the first photo of a nuthatch outside a nest box.
Like the ash-throated flycatcher, nuthatches may use a variety of
materials in their nests, including grass and animal fur. I do not have
a photo of nuthatch eggs but the shot of the female on the nest was one
of my favorites. She must have been incubating her eggs because she was
not inclined to leave the nest that day. |
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House Wren Nest
These wrens build nest of twigs frantically during nesting season. They
build more nests than they need! The problem is, if you are checking a
nest box with a side door, you cannot easily see what is going on
because they build the nest right up to the roof. It is easier to see
what is happening if the box has a removable top. Note the light pink
eggs are nestled in feathers in the back corner of the box. |
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Finding Young Birds
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Western Bluebirds
Shown here are chicks just after they hatch |
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just before they fledge |
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when they are taking flight lessons from their parents after leaving
the nest |
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Titmouse Chicks
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Ash-throated Flycatcher Male &
Chicks
Male near the nest |
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Chicks
almost ready to fledge
Written by Bob Brittain,
July 2009
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