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| Adult Eastern Screech Owl at a nest box |
In the 1970s and 80s, a pair of biologists at Baylor University in Waco, Texas,
Fred Gehlbach and
Robert Baldridge,
were studying screech owl nesting ecology. These small owls nest in
tree cavities and eat a variety of small animals, from insects to mice.
Like most raptorial birds, Eastern Screech Owls usually kill their prey
before bringing it home to feed to their nestlings. Gehlbach and
Baldridge observed some of the screech owls in their study carrying live
Texas Blindsnakes (
Rena [formerly Leptotyphlops] dulcis)
to their nests in experimental nest boxes like those used by wood ducks
and bluebirds (pictured at right). When they checked the nests the next
day, they found, to their surprise, between one and fifteen live
blindsnakes living among the owl chicks in fourteen different nests! In
some cases, the snakes lived with the baby owls for at least a week!
Many of the blindsnakes bore scars from adult owl beaks, but few had
been killed.
If you're not familiar with blindsnakes (aka scolecophidians), don't
worry; few people are. There are about 400 species of these 'seriously
strange serpents',
as Darren Naish calls them over at TetZoo,
distributed chiefly in the world's tropical regions (the Texas
Blindsnake is one of the few temperate exceptions). Most have small eyes
(or none at all, as their name suggests),
smooth round scales,
and eat invertebrates. Their jaw architecture is entirely unique: their
jaws act like little scoops to effectively shovel ant and termite
larvae and pupae into their mouths. Check out the video from BBC's Life
in Cold Blood below, or visit
the homepage of blindsnake biologist Nate Kley at Stony Brook University.
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| Almost as cute as baby snakes |
How does this help baby screech owls? Gehlbach and Baldridge wanted to
find out, so they measured the diversity and abundance of invertebrates
in the owl nests with and without live blindsnakes, as well as the
health and survival of the baby owls (which they were already
measuring). They found that nests with blindsnakes had significantly
fewer mites, insects, and arachnids, and that baby owls from these nests
were 25% more likely to survive and grew as much as 50% faster; in
other words, the presence of the blindsnakes improved the health of the
baby owls and the fitness of the adults. The effects were more
pronounced for the youngest owl babies, which hatch as many as six days
later than their oldest sibling. As the nail in the coffin, Gehlbach and
Baldridge tested whether or not the blindsnakes actually ate the
invertebrates they found in the owl nests, and sure enough, they chowed
down on the soft-bodied fly larvae that kill baby owls in nearly 30% of
nests.
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| Texas Blindsnake (Rena dulcis) |
They also noticed that blindsnakes were more likely to be found in nests
after it rained, probably because the mother owls had an easier time of
finding the blindsnakes when they were crawling around on the surface,
which many fossorial snakes tend to do when rainwater fills their
burrows. Gehlbach and Baldridge also found that blindsnakes could only
survive about two weeks in owl nest boxes that did not contain baby
owls, suggesting that they were dependent on insect larvae that entered
the nest inside food brought by the mother owl. These snakes can climb
trees, so presumably it isn't too challenging for them to climb down out
of a nest box after it is vacated by owls; one gravid female blindsnake
was found in a nest box, so it is possible that they lay their eggs
there before leaving. Some nests contained dead blindsnakes, which
Gehlbach and Baldridge hypothesized had been eaten by the baby owls
after their food supply had run out. In feeding experiments, baby
screech owls readily consumed dead blindsnakes as well as other snakes
of similar size, such as Rough Earthsnakes (
Virginia striatula).
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| Skull architecture of Rena dulcis |
The skulls of blindsnakes are just amazing, and it's thanks to the research efforts of
blindsnake anatomist Nate Kley of Stony Brook University
that we know so much about them. Kley has characterized the feeding
behavior of two families of blindsnakes, the Leptotyphlopidae, which use
scooping motions of the lower jaw known as
mandibular raking, and the Typhlopidae, which use similar motions of the upper jaws, called
maxillary raking.
It's remarkable how similar the two strategies are given that the
snakes are using entirely different parts of their bodies to employ them
and that they are
separated by about 110 million years of evolution. High-resolution CT scans of the skill of
Rena dulcis are also available from
the good people at UT Austin's DigiMorph project.
The jaws (upper in typhlopids, lower in leptotyphlopids) move about
independently of the skull to a remarkable degree. You can get a really
good idea of that motion by watching videos of leptotyphlopids
here,
here, and
here, and of typhlopids
here and
here.
As soon as they're in the mouth, those larvae are goners! These snakes
are unlike all others in that they eat huge numbers of prey items very
quickly, thanks to their unique jaw architecture. One Blackish
Blindsnake (
Austrotyphlops nigrescens)
from Australia was recorded to have eaten over 1,431 ant larvae/pupae
in one sitting! Some blindsnakes have cloacal secretions that aid in
repelling attacking ants or chemically camouflaging the blindsnakes,
which live inside ant mounds. The list of amazing attributes goes on and
on - and there is much more for scientists to find out!
ACKNOWLEDGMENTS
Thanks to
Count_Strad, Toby Hibbits, Gary Nafis, and Nate Kley for use of their photos and figures.
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