The Encounternet tag. Image: University of Washington

If
two birds meet deep in the forest, does anybody hear? Until now, nobody
did, unless an intrepid biologist was hiding underneath a bush and
watching their behavior, or the birds happened to meet near a research
monitoring station. But an electronic tag designed at the University of
Washington can for the first time see when birds meet in the wild.

A
new study led by a biologist at Scotland’s University of St. Andrews
used the UW tags to see whether crows might learn to use tools from one
another. The findings, published last week in Current Biology, supported
the theory by showing an unexpected amount of social mobility, with the
crows often spending time near birds outside their immediate family.

The
study looked at crows in New Caledonia, an archipelago of islands in
the South Pacific. The crows are famous for using different tools to
extract prey from deadwood and vegetation. Biologists wondered whether
the birds might learn by watching each other.

The results, as reported by St. Andrews,
revealed “a surprising number of contacts” between non-related crows.
During one week, the technology recorded more than 28,000 interactions
among 34 crows. While core family units of New Caledonian crows contain
only three members, the study found all the birds were connected to the
larger social network.

The new paper is the first published study using the UW tags to record animal social interactions.

“This
is a new type of animal-tracking technology,” said co-author Brian
Otis, a UW associate professor of electrical engineering whose lab
developed the tags. “Ecology is just one of the many fields that will be
transformed with miniaturized, low-power wireless sensors.”

Biologists
normally tag animals with radio transmitters that broadcast at a
particular frequency, and field researchers use a receiver to listen for
that frequency and detect when the animal is present. An encounter
between small animals would only be recorded if the researcher was
nearby.

The UW system, called Encounternet, uses programmable digital tags that can send and receive pulses.

“Encounternet
tags can monitor each other, so you can use them to study interactions
among animals,” said co-author John Burt, a UW affiliate professor of
electrical engineering. “You can’t even start to do that with other
radio-tracking technology.”

Other
research groups are using the UW tags around the world. Researchers at
the University of Windsor in Canada are using them to study mating
behavior in Costa Rican long-tailed manikins; a researcher at Drexel
University is using them to study the interaction between birds and army
ants in Costa Rica; German researchers are putting the tags on sea
lions in the Galapagos Islands to study their behavior as they pull up
on beaches; and researchers in the Netherlands are studying the social
behavior of great tits, a small woodland bird.

“It’s
a big topic right now, the idea that animals have social networks,”
Burt said. He has been working with field biologists for the last three
years to deploy the tags.

“There
are other tags that can do proximity logging, but they’re all very big
and for larger animals. None is as small as Encounternet – or even near
to it.”

.

A study led by St. Andrews University in Scotland tagged New Caledonian crows to learn about their social behavior. Image: C. Rutz, St. Andrews University

The
smallest of the UW tags weighs less than 1 gram (0.035 ounces) and can
be used on animals as light as 20 grams (less than an ounce), about the
weight of a sparrow. Researchers attach the tags to birds with straps
that degrade and harmlessly fall off after the battery dies. The tag
records nearby pulses, and the signal strength gives an estimate of the
other animal’s distance.

A
typical study using the system includes a few dozen tags and between 10
and 100 fixed base stations. When tagged animals pass a base station
the data is transmitted wirelessly from the tag to the base station, and
from there to the Internet. Researchers can also reprogram the tags
remotely – for example, they can look at initial results to see when
there are few encounters happening, and turn the battery off during
those times to conserve power.

Burt
completed his doctorate at the UW in 2000, with a dissertation on
birdsong communication and learning. He wished that there was a way to
automatically monitor bird interactions in the wild, and in 2005 joined
forces with Otis, an expert in small, lightweight, low-power
electronics. Burt managed the project to develop the tags, with funding
from the National Science Foundation, as a research scientist in Otis’
group.

This
fall they founded Encounternet LLC in Portland, Ore., where Burt now
lives. He is working to add a GPS component to record the location of
encounters, and to add an accelerometer and other sensors that could
detect an animal’s behavior.

“People
are excited about this because for the first time, it allows them to
study smaller animal interactions and social networks on an incredibly
fine scale,” Burt said. “Social networks are turning out to be key to
understanding many animal behaviors. People say Encounternet is the only
thing they can find that can collect that information.”

Automated mapping of social networks in wild birds

Source: University of Washington