New GPS mini-tracker facilitates investigation into movement of smaller animals

Wednesday, July 4th, 2012

In response to the needs of researchers studying smaller animals, a new GPS mini-tracker weighing 5.8 grams has been developed. Like the older tracker, the new device is capable of measuring GPS location, acceleration and internal temperature of the device, but now within a smaller and lighter package.

The accelerometer has been redesigned with an adjustable sample rate enabling higher resolution acceleration sampling (20 or 50 samples per second). The ability to collect 50 samples per second is vital when studying smaller species with faster movements, like birds with high wing beat frequencies.

Black-tailed Godwit (Limosa limosa) with the new GPS mini-tracker

A Black-tailed Godwit tagged with a GPS mini-tracker

The weight of the device is partly determined by several optional features, such as the addition of strap eyes necessary for using a harness to mount the logger to the animal. The mini-tracker can be glued to the animal thereby eliminating the 0.5-gram strap eyes. Weight increases slightly if an internal chip antenna is selected instead of a flexible external antenna.

Battery choice also influences weight; the user can choose between 10 mAh, 30 mAh or 65 mAh batteries, depending on their research needs. A larger battery is essential for collecting measurements in low-light situations such as during cloudy weather, winter in northern latitudes and nighttime. In contrast, choosing the 10 mAh battery and excluding the strap eyes can result in a device weighing as little as 5.8 grams. The “heaviest” tracker weighs about 7.5 grams. The batteries are charged by two independently controlled solar cells.

The memory of the device is eight times larger than the original GPS loggers (now 32 MB) allowing for the storage of approximately 320,000 fixes before downloading data becomes necessary.

In addition, a three-axis earth magnetic compass sensor is under development which will allow data to be collected on the compass direction and vertical/horizontal orientation of the animal, useful for determining the body angle of birds flying in a crosswind. The device’s design also permits the placement of additional sensors for measuring air humidity and pressure, at the user’s request.

Currently four prototype trackers are flying around. Two trackers were placed on Black-tailed Godwits that were tagged in Friesland (NL) and recently left for Africa. Two other trackers were used on Caspian Terns, tagged in Fagelsundet (a small island west of Sweden). Some more prototypes will be used on Eleanora’s Falcons and on Honey Buzzards later this year. We expect that the trackers will be available for other projects by the end of 2012.

Edwin Baaij of the University of Amsterdam Technology Center working on a GPS mini-tracker

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