DO BIRDS BUILD NESTS WITH SNAKE SKINS?
May 19, 2013
My husband was excited recently because he witnessed a robin building
a nest by recycling a shed skin from a snake that lives at the foundation
of our house. We're not sure exactly what kind of snake. He's three
feet long and darkish but is kind of shy and goes back in the hole when
we get close. We both were surprised that a bird would have anything
to do with any part of a snake, living or not. It was amazing how much
skin the bird stuffed in its beak before flying off to the nest, where
it incorporated the shed skin in with twigs and dead grass. Any thoughts
on why a bird would do such a thing? We live in Clarksville, Tenn.
Great question and even greater observation--I am not aware of robins
joining the ranks of birds using snake skins during nest building to
scare off predators, which is the explanation for the phenomenon, but
several bird species are known to do so. The great crested flycatcher
places a shed snake skin in its nest and leaves it there until the young
have fledged. Tufted titmice and blue grosbeaks have been reported to
do the same on occasion. Flycatchers, which nest in tree holes (or bird
boxes), will often drape a snake skin on the outside of the nest cavity,
as well as weaving part of it into the nest itself.
is the response I gave a few years ago to a similar question about birds
using snake skins in their nests. Ornithologists at Arkansas State University
speculated that the snake skin is a deterrent to would-be egg predators
that might themselves become prey to snakes. The scientists conducted
a convincing study that identifies a predatory culprit and suggests
that the use of a snake skin as a greeting card is an effective deterrent.
of animals that encompass most of the geographic nesting range of the
great crested flycatcher are rat snakes and flying squirrels. Flying
squirrels will eat bird eggs, and rat snakes will prey on flying squirrels.
Rat snakes would eat a bird egg, but flying squirrels are probably a
greater threat. The investigators put up 60 nest boxes and placed quail
and simulated eggs of modeling clay in each. They placed one or more
snake skins in the nest in 40 of the boxes; 20 nest boxes had no snake
supported the contention that snake skins deter flying squirrels from
entering a bird nest and eating the eggs. None of the 40 nests with
snake skins were attacked. Flying squirrels ate eggs in 20 percent of
the nests without snake skins.
a doctoral student from the University of Illinois who conducts research
on snake predation on birds at the Savannah River Ecology Laboratory,
has observed what he calls "a sad twist" on bird behavior
that attempts to use snake skins to ward off predators. He says that
"birds, particularly Blue Grosbeaks, on the Savannah River Site
have certainly adopted this strategy [but] we see most of our grosbeaks
incorporating cellophane wrappers, flagging tape, or other bits of litter
into their nests. Perhaps they are fooled by these clear bits of debris
into thinking they are snake skins." One of the goals of Brett's
research is to determine if "blue grosbeaks that successfully incorporate
snake sheds in their nests are more likely to avoid predation"
of their nests. Or will a piece of cellophane fool a nest predator?
the ongoing nationwide interest in bird-watching, many ecological mysteries
about birds remain to be solved. Your observation about the robin adds
to our knowledge of which birds use snake skins. And Brett's research
may provide an example of how human litter is negatively affecting the
natural world. By the way, your snake is probably a rat snake, which
in your part of the country would be very dark or even black in color.
They love to eat flying squirrels.
you have an environmental question or comment, email