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Thursday, February 28, 2013

Screech Owls and Blindsnakes: An Unlikely Mutualism

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.

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.

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).

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!


Thanks to Count_Strad, Toby Hibbits, Gary Nafis, and Nate Kley for use of their photos and figures.


Gehlbach, F. and R. Baldridge. 1987. Live blind snakes (Leptotyphlops dulcis) in eastern screech owl (Otus asio) nests: a novel commensalism. Oecologia 71:560-563. <link>

Kley, N. J. 2001. Prey transport mechanisms in blindsnakes and the evolution of unilateral feeding systems in snakes. American Zoologist 41:1321-1337. <link>

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Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.

Thursday, February 7, 2013

Malagasy Leaf-nosed Snakes

Langaha madagascarensis male
Madagascar has been called the "eighth continent" as a result of its large size, unique habitats, and high faunal and floral (not to mention cultural and linguistic) endemism. Of the ninety-six species of snakes inhabiting the island, only two are found anywhere else: one is a sea snake (the widespread Pelamis platura) and the other is a ubiquitous introduced species (the parthenogenetic blindsnake Ramphotyphlops braminus). Most of the rest belong to the subfamily Pseudoxyrhophiinae, and each deserves its own article. But one has to start somewhere, and perhaps the best place to start is with one of the most unique Malagasy snakes, and one of my favorites: Langaha madagascarensis, the Malagasy Leaf-nosed Snake.

Langaha madagascarensis female
Langaha is so unique that it has been placed in its own genus ever since it was described, and was one of only eight1 genera recognized in Bonnaterre's 1790 Ophiologie, a book that covered 224 species of snake. That's right: at a time when snakes as different as wormsnakes, saw-scaled vipers, sea snakes, and blunt-headed tree snakes were being grouped together as "typical snakes" in the genus ColuberLangaha was considered unusual enough to justify its own genus! Today there are three recognized species of Langaha, but the most is known about L. madagascarensis.

Left: Captive juvenile Langaha madagascarensis exhibiting hanging behavior; photo from Krysko 2003
Right: Seed pods of the Ophiocolea floribunda, a Malagasy legume whose genus is Greek for 'hollow snake'
As their name implies, Leaf-nosed Snakes have bizarre nasal appendages. What's more, these structures are sexually dimorphic to a degree unusual among snakes. Female Leaf-nosed Snakes have a more elaborate, serrated nasal appendage, whereas males bear a longer, pointier one. These structures are present at birth, suggesting that they have some function beyond sexual signaling between rival males or potential mates. Often, these snakes are seen hanging from branches with their heads pointing towards the ground - perhaps the structures serve to drain water off the snake? Several Malagasy plants, including some legumes and bignonias, have long pointed seed pods that hang down from the plant, providing possible models that the snake may imitate with its posture and nasal appendage. No one knows for certain.

Male (right) and female
(left) L. madagascarensis 
This is a timely post in that it comes on the heels of newly published research on Malagasy Leaf-nosed Snakes. An article by recent Cornell University graduate Jessica Tingle has just appeared in the journal Herpetological Conservation and Biology documenting novel aspects of the behavioral ecology of this unusual snake. Everything known about the behavior of Langaha to date has been learned from observing captive individuals. Tingle's paper presents the first data collected on the behavior of Langaha in the wild. She observed several of these snakes foraging for and eating lizards, although one sentence in her paper stands out to me as typical of snake behavior studies: "The vast majority of their time (90%) was spent not moving at all." Although this sounds boring, it provides evidence that these snakes are primarily ambush predators, rather than active foragers (although Tingle did observe one Langaha chasing skinks on the ground). Spending months in Madagascar, Tingle was able to observe only a few snakes, and much remains to be learned about their natural history and ecology.

Plate showing a male Langaha madagascarensis from Bonnaterre's 1790 Ophiologie
From observations made on Langaha in captivity by Kenney Krysko of the Florida Museum of Natural Sciences, we know that Leaf-nosed Snakes lay eggs. When they hatch, the nasal appendages of juveniles are folded up so that their egg tooth can be used to break out of the egg. The appendage gains its normal shape after 36 hours. Juveniles exhibit the same vertical 'hanging' behavior as adults, which Krysko also suggests helps them mimic the seed pods of Malagasy plants (and perhaps deter predation, though by what predator is unclear).

Hatchling Langaha madagascarensis, from Krysko 2003
The other two species of Langaha are very poorly known. In Darren's TetZoo article, he states that only female Langaha alluaudi have nasal appendages, but I have been unable to find another source corroborating this fact, although I did find a photo on Flickr purported to be a male L. alluaudi (it looks similar to a male L. madagascarensis, also sometimes called L. nasuta, to me). Female L. alluaudi have longer, straighter nasal appendages than L. madagascarensis, and female L. pseudoalluaudi have shorter, more upturned ones (no word on what male L. pseudoalluaudi might look like). Why these differences? Perhaps differences in microhabitat or sexual preference are the cause. Who can say?

Female (left) and male(?, right) Langaha alluaudi

Female L. pseudoalluaudi

Although Madagascar is unique, it is similar to the rest of the world in at least one sad way: its natural places are disappearing quickly. Most of its forests have already been logged or converted to slash and burn agriculture, and what little remains is dwindling daily. If more effective conservation measures are not taken,  including supporting the human communities that depend on the rich natural resources of this hottest of biodiversity hotspots, we may never find out what Langaha's nose is for.

Male L. madagascarensis consuming Chalarodon madagascariensis
Photo from Herp. Con. Bio. gallery for Tingle 2012

1 Three of these eight genera turned out not to be snakes at all: the limbless lizards Anguis and Amphisbaena, and  the limbless amphibian Caecilia.


Thanks to Dick Bartlett, Jessica Tingle, David d'OBernard DupontRussell Speight, and G.E. Schatz for use of their photos.


Bonnaterre PJ (1790) Ophiologie, in Tableau encyclopédique et méthodique des trois règnes de la nature. Panconoke, Paris <link>

Krysko KL (2003) Reproduction in the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae). African Journal of Herpetology 52:61-68 <link>

Krysko KL (2005) Feeding behaviour of the Madagascar leaf-nosed snake, Langaha madagascariensis (Serpentes: Colubridae: Pseudoxyrhophiinae), with an alternative hypothesis for its bizarre head structure. African Journal of Herpetology 54:195-200 <link>

Tingle JL (2012) Field observations on the behavioral ecology of the Madagascan Leaf-nosed Snake, Langaha madagascariensis. Herpetological Conservation and Biology 7:442-448 <link>

Creative Commons License

Life is Short, but Snakes are Long by Andrew M. Durso is licensed under a Creative Commons Attribution-NonCommercial-NoDerivs 3.0 Unported License.