A group of Jackdaws and some Rooks flying towards a night roost.
In a previous post I told about our new project on Jackdaws and gave some information on the biology of these birds. I also mentioned that we attached GPS-loggers to some birds.

But what are GPS-loggers? How do they work? And why did we attach them to some birds?

A GPS-logger takes GPS-positions at a pre-programed schedule and stores the data. It works like the hand-help GPS device you may use for hiking, the one that is included in your smartphone or the one in your navigation system of your car. When you plot all the points that you collect you can see the route that you took. This is exactly how the GPS-loggers for animals work. The only difference is that the GPS-loggers we use are much smaller and weigh only a few grams. This enables a scientist to attach them to a bird. Birds can carry the loggers without being handicapped. If a bird flies around for some time with such a logger and you later retrieve the data, you can see when and where the bird was. With the help of such little tracking devices biologists can learn a lot about the movement patterns of animals that would otherwise be impossible to unravel.

In the cases of the Jackdaws, the GPS-loggers take very many points. I have programmed them on as much as one GPS-point per 15 minutes. Maybe does not sound that much, but it does this for 24 hours a day, 7 days a week. Over a whole year this makes more than 35.000 data points. This enables us to get a high spatial and temporal resolution of the bird’s movements and we can learn much about where they sleep, where they collect food, where they winter and so on.

Taking that many GPS-points requires a lot of energy. Since batteries of the loggers need to be small to keep the weigh as low as possible, the loggers have small solar panels that charge the battery.

The GPS-loggers we use for the Jackdaws have another very valuable function. Using an antenna one can download the data from the distance! Thus there is no need to recapture the individuals to get access to the data. You “only” need to get close (within about 300m) to the birds and you can download the data to your laptop. This is a very valuable function since recapturing the animals is often a problem.

The Jackdaws are a very convenient bird to download data. In the evenings, often hundreds or even thousands of birds come together to sleep on a communal roost. When I find such a roost, I can go there with my antenna and laptop. If I am lucky “my” birds are on the roost and I can download the data. Recently I have been very lucky and found almost all of the birds carrying GPS-loggers on one roost. Within one evening I downloaded thousands of datapoints. From these data we learned already a lot about what the birds do after the breeding season. For example, even though the Jackdaws do not need their nestbox at the moment, they still visit the colony regularly for a short visit. For most part of the day, however, they are moving around in the surroundings of the colony. The furthest distance to the colony was 21 km so far. It will be exciting to see what happens during the winter. 
Jackdaw with GPS-logger

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