The snake that decapitates its prey

by Herp News on July 30, 2015

Snakes are impressive predators. They have super-flexible jaws that allow them to capture prey animals of all sizes. And once they do, they usually swallow their prey whole – whether it’s a small rat, or a large deer.

There are some exceptions to this behavior. Some snakes prefer to break their food down into smaller pieces instead of swallowing them whole.

The brahminy blindsnake (Indotyphlops braminus) is one such example. These tiny, worm-like snakes rip their preys’ heads off before swallowing them, a new study published in the Journal of Zoology has found.

Bhraminy blindsnakes are native to Africa and Asia, and live their lives completely underground. Because they have no need for normal eyesight, their eyes have nearly vanished, rendering them almost completely blind. Bhraminy blindsnakes are also distinctive in that the species consists entirely of females that reproduce asexually via a process called “parthenogenesis,” in which embryos develop from unfertilized egg cells.

And now, decapitation has been added to the bhraminy blindsnake’s list of peculiarities.

“I first found this behavior in the blindsnakes about a year ago,” Takafumi Mizuno, lead author of the study from the Kyoto Institute of Technology in Japan, told mongabay.com. “And I was really surprised.”

To investigate this behavior further, Mizuno and his team collected seven blindsnakes from Hachijo-jima Island in Japan. They placed these snakes inside a plastic cage, introduced termites (Reticulitermes speratus) into the cage, and then videoed the snakes’ eating habits.

Generally, snakes swallow the head of their prey first. But Mizuno’s team found that the blindsnakes grasped the termites from behind, instead of the head, and ate them in such a way that the termite heads would stick out of their mouths.

Then, in nearly half of the feeding bouts, the blindsnakes rubbed the termite heads on the base of the plastic cage, and decapitated them. Even in instances that the snakes did swallow the termites whole, some vomited out the partially digested termites, and then beheaded them.

Sequential photos of a feeding event where a blindsnake decapitates a termite: (a) a blindsnake starts ingesting a termite from its abdomen; (b) the termite is transported into the mouth of the blindsnake; (c) the termite abdomen comes to lie in the oral cavity but its head remains outside of the mouth; (d) the blindsnake rubs the termite’s head against the bottom of the cage, which results in decapitation. Scale bar represents 2 mm. Source: Mizuno and Kojima, 2015.

But decapitation probably does not make it any easier for the snakes to swallow their prey, the authors write. This is because, in the experiments, it took the snakes about the same time to finish one termite serving, regardless of whether they swallowed the termites whole or decapitated them.

What advantage does decapitation have then?

The authors have put forward two possible explanations. First, the termite heads might be difficult to digest, they write. Blindsnakes eat a large number of animals during one feeding bout, so the authors speculate removing indigestible parts on the plate might be a smart move.

The second reason why blindsnakes might be decapitating the termites could be because the termite heads contain toxic compounds, according to the authors.

The most likely reason of the two remains unclear. But this unique decapitating behavior puts these blindsnakes in the exclusive company of just a few other prey-tearing snakes.

A blindsnake lies among termites, which have heads…for now. Photo courtesy of Takafumi Mizuno.

Some crab-eating snakes like the crab-eating water snake (Fordonia leucobalia) and cat-eyed watersnake (Gerarda prevostiana), for example, tear apart crabs into smaller bite-sized pieces before eating them.

But blindsnakes and crab-eating snakes are not close relatives. They are in fact far apart on the evolutionary tree. How did they then develop similar behavior?

According to the authors, this trait would have evolved independently in the two groups of snakes. But the common feature that links crab-eating snakes with blindsnakes is that they all feed on arthropods – segmented animals that include insects, spiders and crustaceans.

“The legs of most species of crabs break off quite easily, and for a wide variety of arthropods the bodies of the animals break much more easily at the joints between different parts of the exoskeleton, rather than within a single part of the exoskeleton,” Bruce Jayne, a professor at the University of Cincinnati in the U.S., told mongabay.com. “Such weaknesses appear to be exploited both by blindsnakes in the current study and both species of crab-eating snakes.”

Despite this common feature between the distantly related snakes, their behaviors have some interesting differences, he added.

For example, crab-eating water snakes usually pin down hard-shelled crabs to the mud, break their legs off, and then swallow each leg one by one. For these snakes, the hard-shelled crabs are too large and awkwardly shaped to swallow whole. So it makes sense to eat the crab legs first, since these are easier to break off. On the other hand, blindsnakes are physically capable of swallowing the small termite prey whole. But they choose not to, on most occasions.

The cat-eyed water snake shows another interesting variant, Jayne said. This snake often rips apart the external shell of freshly-molted or soft-shelled crabs in places that do not necessarily correspond to the easily-detachable joints, he added.

But whatever the differences, discovery of blindsnakes’ strange eating habits tells us that there is a whole lot about snakes that we still don’t know.

“This study is a nice example of how much basic natural history we still have to learn,” Jayne said. “Who knows what other fascinating secrets remain to be discovered in the future?”

 

Citation

  • Mizuno, T. and Kojima, Y. (2015), A blindsnake that decapitates its termite prey. Journal of Zoology. doi: 10.1111/jzo.12268

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Build Your Own RFID

by Herp News on July 30, 2015

Jay_feeder_TomSmall

Last month, we highlighted wildlife tracking hardware and software that allows near-real-time monitoring of tagged animals, through frequent GPS location data and spatial algorithms that learn an animal’s typical behavior and alert researchers to a sudden change in movement speed or location.

However valuable such data are, researchers that study the behavior of individual animals often must infer findings from the activity of small study samples due to the high cost of tracking technology. GPS tags also require substantial (i.e. heavy) batteries, limiting their use for birds and other small animals.

As an alternative for researchers on tight budgets, Dr. Eli Bridge at the University of Oklahoma has developed a customizable Radio Frequency Identification (RFID) reader that you can build yourself at a very low cost. RFID reader systems identify and monitor the movement of people, animals, or items bearing tiny tracking tags by checking for the presence of tags at various reading stations, recording the tag’s unique identification number, and logging the data until they are downloaded.

RFID race tag_on runner_rupp.de-WikimediaCommons

An RFID chip worn on a triathlete’s ankle strap at right is read by the receiver on the left to record their start, finish, and passing by of course markers. Photo: rupp.de, Wikimedia Commons

 

Commercial applications of RFID technology have been common since the 80’s – it is found in badges worn by medical or security staff, electronic toll readers, and hotel or office entry key cards. Only recently have scientists begun to apply RFID to wildlife research beyond merely mark-recapture purposes. Bridge has created a website that provides information and instructions to build the reader system, ranging from a list of parts to a complete circuit board design and accompanying instructional videos. The website is directed specifically at animal researchers with limited budgets.

“People are sometimes surprised when I say that I started with no engineering background and figured out how to build an RFID reader by surfing the Internet,” said Bridge. “But that sort of thing is becoming commonplace. I’ve corresponded with several people, also non-engineers who have done the same thing.”

How does the RFID work?
RFID technology requires three main components: a uniquely identifiable tag, a reading device with an antenna, and software. A passive integrated transponder (PIT) tag is activated as it comes into contact with the electromagnetic field created by the antenna. When the tag passes near a reader, it is activated to send its unique alphanumeric code to the reader module that is then stored in a memory chip.

The system uses radio waves to capture data from the tag, so while the tag must be relatively close to the reader to be recognized, it doesn’t need to be in line of sight.

Use in the field
To integrate this technology into a biological study, a researcher attaches the tag to an animal and places the tag reader in a spot that is regularly and reliably visited by tagged individuals, such as a nest, den, or birdfeeder. The researcher sets the amount of time the unit will spend reading (probing the antenna’s range for a tag) and resting (intervals in between read attempts) to best balance the collection effort and energy use. The more time the system spends reading, the more battery it will use. If you are placing the antenna at the entrance to a nesting cavity where birds typically pass by through quickly, intervals will have to be set shorter. If you are looking at tortoise movement through culverts, you will have a little more time!

cheapRFID_in waterproof case_animalmigration dot org

Waterproofing on the cheap: the DIY RFID ready for the field Photo: Eli Bridge, University of Oklahoma

 

Although Bridge and his colleagues designed this do-it-yourself reader with birds in mind, it can be applied to a wide range of taxa. The tag does not require batteries and so is both lightweight and has a theoretically unlimited lifespan. Its biggest constraint comes from the small antenna size (approximately 12 cm) and short reading range (10 cm), though these values are comparable to off-the-shelf models, such as these and these, that would cost between several hundred to several thousand U.S. dollars and are less customizable to situations in the field. Bridge’s system is field-ready, costs about $40 per unit before recurring costs, and can be integrated with a solar panel to reduce battery expenses.

Once installed, the system runs by itself, aside from replacing batteries and downloading data. Depending on the data collection settings and the batteries you use, revisits to the reader can be as infrequent as once a week.

Flamm Owl w-RFID tag_RossCalhoun

Deploying an RFID PIT tag within a standard bird band on a flammulated owl   Photo: Ross Calhoun, Colorado College

After you have installed the system and properly attached the tags to your study subjects (Bridge’s website details the steps required to attach the tag to birds), you can start (autonomously) collecting data on the presence of tagged individuals at your sites of interest that are very easy to analyze with limited field maintenance.

RFID-enabled feeders for bird research
Bridge and colleague David Bonter used these systems with a network of bird feeders in New York and logged a total of 500,000 visits over 5 months. The patterns of these visits indicated some specific-specific movement patterns, as well as variability among individuals (certain individuals visited certain readers frequently, while some traveled relatively long distances between tag readers, suggesting emigration).

The design also offers a range of plug-and-play options, allowing the reader to integrate with various environmental sensors, a camera, or a scale that takes weights autonomously. These allow researchers to compare feeding times and rates with environmental variables.

RFID bird feeder_animalmigration dot org

A bird feeder integrated with an RFID reader strategically deployed below it.  Photo: Eli Bridge, University of Oklahoma

Bridge has used his own design creatively in various studies: in one study, he integrated the technology into a smart bird feeder that fed only certain tagged birds to investigate effects of variable food supplementation within a family group. Bridge’s team attached the PIT tags to nesting individuals within a population of birds and deployed a set of feeders that each had an RFID reader and antenna at the base. When a tagged bird landed on the feeder, the reader would identify the bird from its ID number and then dispense food only to certain family members – males, females, or helpers.

By controlling food availability for these three groups, the research team could infer the respective contributions of birds in these different roles to the rearing of young. When they then assessed nestling condition, they could also deduce which family members contributed most to success with or without the supplemental feeding.

The open-source nature of this device requires some initial effort to build and then troubleshoot in the field, but with RFID technology improving rapidly, these devices hold great potential for broader application. By offering a form of tracking animal movements for researchers on a tight budget, they allow for greater collaboration and therefore impact across studies and institutions.

The Bridge reader has now been used on a wide range of species including wood ducks, hummingbirds and sociable weavers, investigating a myriad of topics. I’m really excited about the ongoing push for STEM education, and I think open-source and inexpensive technology is going to contribute a lot to the next generation of innovators and scientists, says Bridge. I’ve never made any money from the RFID readers, but it’s been really worthwhile to see all of the interesting projects that have emerged as a result of keeping the technology free and open.

 

Citations:
Bonter DN. and Bridge, ES. 2011, Applications of radio frequency identification (RFID) in ornithological research: a review. Journal of Field Ornithology, 82: 1–10. doi: 10.1111/j.1557-9263.2010.00302.x.

Bridge ES and Bonter DN. 2011 A low-cost radio frequency identification device for ornithological research. Journal of Field Ornithology 82, 52–59. doi:10.1111/j.1557-9263.2010.00307.x.

Jay_feeder_TomSmall

A pair of Florida scrub-jays, wearing PIT tags, on a selective bird feeder, or Smartfeeder” Photo courtesy of Tom Small, University of Memphis

 

 

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Build Your Own RFID

July 30, 2015

Last month, we highlighted wildlife tracking hardware and software that allows near-real-time monitoring of tagged animals, through frequent GPS location data and spatial algorithms that learn an animal’s typical behavior and alert researchers to a sudden change in movement speed or location. However valuable such data are, researchers that study the behavior of individual animals [...]

Read the full article →

The snake that decapitates its prey

July 30, 2015

Snakes are impressive predators. They have super-flexible jaws that allow them to capture prey animals of all sizes. And once they do, they usually swallow their prey whole – whether it’s a small rat, or a large deer. There are some exceptions to this behavior. Some snakes prefer to break their food down into smaller [...]

Read the full article →

U.S. to strengthen restrictions elephant ivory

July 30, 2015

In response to growing concerns about elephant poaching, President Obama today announced a new push to limit the ivory trade in the United States. In a joint press conference held with Kenyan President Uhuru Kenyatta, Obama said the U.S. Fish and Wildlife Service is proposing a new regulation that “bans the sale of virtually all [...]

Read the full article →

U.S. to strengthen restrictions elephant ivory

July 30, 2015

In response to growing concerns about elephant poaching, President Obama today announced a new push to limit the ivory trade in the United States. In a joint press conference held with Kenyan President Uhuru Kenyatta, Obama said the U.S. Fish and Wildlife Service is proposing a new regulation that “bans the sale of virtually all [...]

Read the full article →

Nine months in, how has Jokowi fared on the environment?

July 30, 2015

[dropcap]N[/dropcap]ine months into the landmark presidency of Joko “Jokowi” Widodo, Indonesia’s first head of state to emerge from neither the political elite nor the military, the hope that ran to such a fever pitch during his campaign has dimmed somewhat, eroded by his handling of tussles with the police and his political party and by [...]

Read the full article →

Nine months in, how has Jokowi fared on the environment?

July 30, 2015

[dropcap]N[/dropcap]ine months into the landmark presidency of Joko “Jokowi” Widodo, Indonesia’s first head of state to emerge from neither the political elite nor the military, the hope that ran to such a fever pitch during his campaign has dimmed somewhat, eroded by his handling of tussles with the police and his political party and by [...]

Read the full article →

Conservation win in Madagascar: 7 new reserves established

July 30, 2015

Indri Lemur. Photo by David Cook. Good news on the environmental front in Madagascar has been rare and fleeting in recent years, but today the Indian Ocean island’s Prime Minister gave conservationists a bit of hope by officially decreeing seven new reserves that target critical habitats for endangered lemurs, chameleons, and frogs. The seven reserves, [...]

Read the full article →

Conservation win in Madagascar: 7 new reserves established

July 30, 2015

Indri Lemur. Photo by David Cook. Good news on the environmental front in Madagascar has been rare and fleeting in recent years, but today the Indian Ocean island’s Prime Minister gave conservationists a bit of hope by officially decreeing seven new reserves that target critical habitats for endangered lemurs, chameleons, and frogs. The seven reserves, [...]

Read the full article →