Monitoring of bears
The bear is a shy animal that moves over extensive areas. To monitor them we equip them with radio transmitters or GPS-receivers. Until 2003 we used only the traditional VHF technology (i.e. radio transmitters). Since then we have replaced more and more of those with GPS-collars.
The bears that still have regular radio transmitters are currently located one to two times per month during the non-denning season. This low level of monitoring is sufficient to continue the long-term demographic study of the population. It gives us a rough idea of their use of area, documentation of their dispersal, and we can also locate a bear and determine the reason for its death. Mainly female bears are included in this study and we mark their yearlings in the spring, before they have separated from their mother. Thus we can keep track of bears and their kinship through generations. We study the survival of cubs and the time of separation by tracking the radio-marked females with a helicopter to observe them and count their cubs. We count cubs three times per year; 1) in spring after they have left the den, 2) in summer following the mating season, and 3) in fall before they enter the den.
The bears with GPS-collars give us a whole different flow of data, compared to those with radio transmitters. As a standard we have programmed the GPS-receiver to take a position every 30 minutes during spring, summer and fall, and one position per day during winter, while the bears are in the den. The GPS-positioning schedule can be reprogrammed for a more or less frequent positioning, depending on which study the bear is included in. Very frequent and exact positioning enables us to more precisely and on smaller scales than before study aspects of bears’ biology, such as their movements through the landscape, behavior, predation and habitat selection. By having many bears equipped with GPS-collars simultaneously in the same area, we can also study the interactions among bears and how they are effected by gender, kinship, and season.
a) Radio transmitters
With a receiver that picks up VHF radio signals, we manually localize (radio-track) bears with radio transmitters from a distance. By triangulating directions of the signal, we estimate the position of the animal (generally within a few hundred meters accuracy). To receive the transmitter signal from ground, we must be within a few kilometers, or sometimes a few hundred meters, from the bear, depending on terrain. We mainly radio-track from cars, though depending on study and area, we may also radio-track from an airplane. As bears move over extensive areas, it requires a high investment of time and fuel to manually radio-track them. When tracking from a car, the search is restricted to areas with roads and quite often bears are not found. In addition, manual tracking is often restricted to day-time hours and/or certain seasons. Hence one gets a limited amount of positions per each bear during confined periods. The benefits with the traditional radio transmitters are that they are uncomplicated, robust, have a long life span (the battery lasts 4-5 years), and they are relatively cheap.
GPS (Global Positioning System) is a satellite navigation system. By receiving signals from satellites, the GPS receiver calculates its position in longitude, latitude and elevation. The GPS technology has in many aspects revolutionized wildlife research. The GPS-receiver on the animal can take positions very accurately and frequently, without restrictions to specific periods. Hence one will get a very precise picture of the animal’s movements independently of time of day and area. However, each positioning requires battery power, making the positioning frequency a trade-off between how often one needs positions for the study and how long one needs to collect data from that bear. The disadvantage of GPS-collars is that they are technically complicated and not as robust as the radio-collars, and they are very expensive.
In this project we use GPS-collars that, apart from a GPS receiver, also have a GSM-module, radio transmitter, and an activity sensor. All position and activity data are saved in the GPS, and the GSM module sends the latest positons as an sms to a receiving station. The researchers can access all the data by linking to a database that is connected to the receiving station. The radio transmitter is only turned on when we need to track the bear manually. The activity sensor measures the bear’s movements in X and Y axis, and can give us a rough estimation of the bear’s level of activity.
In our Northern study area the GSM coverage is very limited. There, instead of GPS/GSM, we use GPS/Iridium collars that send the bear’s latest positions via satellites to the receiving station.
c) Implant – intraperitoneal radio transmitters
Currently subadult bears and bears with GPS-collars receive a radio transmitter that is surgically implanted into their peritoneal cavity, a so-called implant. The reason for equipping subadult bears with implants is to avoid capturing them every year while they are still growing, which is necessary if they receive a radio-collar. Bears with GPS collars receive an implant as a back-up to find them again, should their GPS-receiver fail. As the GPS-receivers continue to be improved, we hope that soon it will not be necessary for us to use an implant as a back-up.
Studies made within this project have shown that, in some cases, the implants needs to be replaced after 5-6 years, which also is the extent of the battery capacity. Nowadays our routine is to remove the implants after 3-5 years.