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Animals display many remarkable behaviours. To better appreciate their talents, how often have we wished that these creatures could communicate with us? We would love to know where they go during migrations, for example. In recent years however, animal ecologists have developed techniques to allow us to track some of these creatures. As a result, these animals communicate with us simply by doing what comes naturally, during the course of which our little espionage devices report where the animals have gone.

During the 1960s radio tracking of some large animals like grizzly bears was tried near Yellowstone National Park in the western United States. These large animals were ideal in that they were large enough not to be inconvenienced by the extra load of radio transmitters with battery packs. Wildlife managers sought to document bear reactions to livestock grazing, logging and recreational activities. Thus during 1975-76, a number of bears were trapped, fitted with radio transmitters and released. A small plane equipped with rotatable antenna was used to track the bears.  From the data, it was discovered that the bears exhibited a lot of variety in their behaviours . The popular habitat types included thick forest and wet meadows and the size of territory they occupied varied from 26 to over 700 square kilometers.  Of 16 instrumented bears, 14 routinely crossed into and out of the national park. (Judd and Knight. 1980. Ursus 4: 359-367)

Clearly radio tracking had demonstrated that valuable information could be obtained from tagged animals. The trend since then has been to tag and track smaller and smaller animals, many of them in populations whose numbers are threatened, including many migratory birds. In order to mitigate threats to these birds, it would be useful to know their flight paths and destinations.  Nevertheless, at first the devices were too large for really small birds.

Aircraft are clearly out of the question as a means of tracking birds that fly long distances over the sea.  In the 1980s, a device was developed to track elephant seals. The device, called a geolocator, was designed to regularly measure and record ambient light levels. Such recordings over time can be used to calculate latitude and longitude. Once the recording device is recovered from the animal, computers calculate latitude from the day length, and the light level at mid-time between dawn and dusk is used to calculate longitude. The system requires battery power to store the data, but this can last up to five years. The fact that the system does not broadcast to satellites, means that the devices can be lightweight and cheap.

It was a long way from the tracking of elephant seals to the tracking of small birds. Such new uses were pioneered in the 1990s by the British Antarctic Survey which first used geolocators on juvenile wandering albatrosses. By 2007 such devices had been reduced to 1.4 grams, suitable to track small birds like the artic tern, which weighs about 125 grams.

The traditional way to study bird activities has been bird banding. Based on such studies of recovered bird bands, scientists believed that arctic terns were remarkable long distance travellers. During the summer of 2007, a Danish team trapped and attached plastic leg rings (geolocators) to 50 terns on an island near Greenland and 20 birds on an island near Iceland. The following year, after the birds had completed their outward and return migrations, 11 birds with geolocators were trapped again.  Ten of the eleven loggers retrieved, were successfully downloaded, each  providing a full year of migration data.

It transpires that the artic tern has amazing talents!  The average distance travelled by these birds in one round trip was 71,000 km with average distances of 520 km per day. Since Arctic terns often live 30 years, the total distance traveled in a lifetime may exceed 2.4 million km. (Egevang et al. 2009. Proceedings of the National Academy of Sciences 107 #5 pp. 2078- 2081) Not only did the tagged birds travel so far, but they even returned to the same nesting site as the previous year. This is how the Danish team knew where to find the returning birds.

Scientists continue to develop ever smaller tracking devices. Obviously moist frog skins do not provide good anchorage, so scientists in Australia in 2012 surgically implanted tiny devices into three species of tree frog. However when the scientists recaptured the frogs about three weeks later, with the objective to recover the devices, they found that three quarters had entirely lost the devices! Others had the devices now located in the bladder, preparatory to being eliminated in the urine. Subsequent testing revealed that the frogs developed extensions from the bladder that engulfed foreign objects in the body cavity and drew them into the bladder. Who knew research could be so fraught with hazards?

The tracking of young snowy owls was the item which first attracted my attention. These birds were forced by population pressure south from the Arctic into central North America. Some of these animals were then tagged with solar-powered GPS transmitters that sent a data point every half hour to cellphone towers. What the scientists discovered is that these huge predatory birds displayed highly individualized behaviour and food preferences. (Pat Leonard. 2014 Living Bird 33 # 2 pp. 20 – 27)

Biologists hope to recover more interesting data from various animals. The work is never easy or cheap however. Nevertheless the insights that we gain always remind us of the children’s hymn “All things bright and beautiful/All creatures great and small/All things wise and wonderful/The Lord God made them all!”


Margaret Helder
December 2014

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