Hilton Jr, who has banded almost 46,000 birds at the Hilton
Pond Center, is holding this female robin on her back in his
hand. He is blowing on her tummy feathers to show the brood patch.
When no one is blowing on them, the outer feathers keep the brood
patch hidden. The robin can control her skin muscles to open the
feathers, so she can put the brood patch directly on her eggs for
feathers for insulation — to keep body heat in, and the cold and
rain out. But the same feathers that hold a mother bird's heat in
could keep her body's heat away from her eggs and her babies!
What can she do to share her body warmth when she's incubating eggs? This
lesson tells you about her special adaptation, the brood patch
(also called the incubation patch). Learn how it works and how
banders can look at the brood patch to get information about a bird.
Little Background About Feathers
A bird's outer body feathers, called contour feathers,
are designed to give the bird its shape and to make a barrier between
the bird's inner, insulating feathers (down feathers)
and the outside world. These outer feathers work like a windbreaker jacket.
The inner, down feathers work like the warm sweater under the jacket,
to trap the body's warmth. Birds have down feathers covering much of their
bodies, but we usually can't see those feathers under the contour feathers.
A tiny muscle attaches to each feather, so birds can fluff out their plumage,
or even "part it" in places.
the Brood Patch Develops
Most female birds, and some males, develop a brood patch during the breeding
season. Changes in hormone levels during the nesting season start the
process. Down feathers on the bird's tummy, and even some contour feathers,
suddenly get very loose. In some species, those feathers just fall out.
In other species the mother pulls them out. Ducks pull them out while
building the nest and use them to make the nest soft and extra warm. Gulls
and shorebirds often have three brood patches. Songbirds and hummingbirds
have one that heats all the eggs.
the feathers fall out, other changes happen too. The tissue in the tummy
area swells. The tissues hold more water, and the blood vessels that feed
the skin expand. These changes make the bird's tummy skin almost as hot
as the body's interior.
Parent Develops a Brood Patch?
In most songbirds, only the female develops a brood patch, but
in a few species the male also does. In species such as hummingbirds,
robins, and jays, only the female incubates eggs. In these species only
the female develops a brood patch. In a few species, such as phalaropes,
only the male incubates; he's the only one who develops a brood patch.
In Barn Swallows, males sometimes help with incubation, but not always.
Those male Barn Swallows that do a lot of incubating often develop a brood
the Brood Patch Works
When an incubating parent sits on the eggs, the skin muscles
open up the brood patch. Then the parent sits down and wiggles its body
back and forth a bit. The sensitive skin feels for the eggs so the parent
can settle where the skin makes best contact with the eggs. In this video
clip, watch a mother robin settling on her eggs and see her wiggle to
get them touching her brood patch:
This! Observing and Journaling
- If you
look at photographs or movies of birds incubating, or if you have an
opportunity to watch a live bird nesting, see if you can see how the
incubating parent moves its body to maximize "tummy contact"
with the eggs. Then describe in your journal exactly what you observed.
How do you think it feels to incubate eggs? How does the brood patch
help the babies survive?
Science Education Standards
and animals have life cycles that include being born, developing into
adults, reproducing, and eventually dying.
- Each plant
or animal has different structures that serve different functions in
growth, survival, reproduction.