Migratory Bird Tracking

Story in the news today about the British Trust for Ornithology (BTO)
installing satellite trackers on cuckoos, the first 2 of which have
arrived in North Africa.

http://www.independent.co.uk/environ...a-2314566.html

They aren't using GPS due to weight restrictions. Rather, they use
Doppler histories over a satellite pass, like the Navy's former
Transit system.

http://www.bto.org/

http://www.bto.org/science/migration...uckoo-tracking

http://www.bto.org/science/migration...ing-technology

"Tags using GPS technology are still too large and power hungry to be
suitable for tracking small flying animals such as many birds. The
latest Platform Transmitter Terminals (PTTs) operating using more
traditional technology are, however, small enough to allow birds down
to almost 100g to be tracked. For the Cuckoo tracking project, we have
used PTTs weighing just under 5g that have been supplied by Microwave
Telemetry Inc. . These operate via the Argos satellite system. . . .

The PTTs transmit basic data about their functioning that is picked up
by the Argos satellites as they pass overhead. Due to the Doppler
effect, a shift in wavelength of these radio transmissions occurs as
the satellite passes overhead and this allows the ground-based part of
the satellite system to calculate the positions of the PTT and the
bird carrying it. This is not as accurate as GPS – typically the best
locations are accurate to within 500m, whereas GPS has an accuracy of
a few metres. It is, however, very accurate on a global and regional
scale and provides a far more reliable and detailed track than other,
slightly smaller, tracking devices such as geolocators."

A story on the BBC web site last month incorrectly stated that the
trackers used GPS:

http://www.bbc.co.uk/nature/13559202

"Scientists from the British Trust for Ornithology are planning to
attach tiny satellite trackers to cuckoos to study their migration
patterns.

.. . . The team will tag five male birds with trackers like tiny
backpacks that weigh just five grams.

The tags have soft straps which fit around the cuckoos' wings.

.. . . The GPS trackers will communicate their whereabouts via a
satellite-based system called Argos, which was specifically developed
to collect environmental data and has been adopted for several
wildlife tracking studies.

.. . . They have caught 10 cuckoos in order to find five that were
large and heavy enough to carry the tags.

'To make absolutely certain we're not harming the birds, we only tag
males that weigh more than 115g,' explained Dr Hewson."

The manufacturer of the trackers used on the cuckoos:

http://www.microwavetelemetry.com/bird/

"In 1991 we introduced our first Doppler PTT, the 95g PTT-100. . . .
By 2001 we were able to reduce the size of the Argos PTT to the point
where a GPS unit could be added to it and still have a PTT light
enough for a bird to carry."

The company's lightest Argos/GPS tracker is 22 grams (~ 3/4 ounce):

http://www.microwavetelemetry.com/bi...gosGPS_22g.cfm

"Internal sixteen channel GPS receiver
GPS accuracy ± 18 m"

http://www.microwavetelemetry.com/bi...ifications.cfm

A US company that makes GPS bird trackers as light as 2 grams:

http://www.telemetrysolutions.com/tr...-for-birds.php

http://www.telemetrysolutions.com/sp...ata-logger.pdf

http://www.telemetrysolutions.com/sp...ata-logger.pdf

Note that the battery life drives the weights. The lighter units
wouldn't be suitable for long duration migrations. Also, these are
mostly data loggers that would require recapturing the test subjects
in order to recover the data. A data transmitter would further reduce
battery life.

Aerodynamic drag is also a non-trivial issue for bird trackers.

Nevertheless, the extremely small size and low weight of these devices
is amazing.