Can you tell me all about satellite collars and why scientists use them?
We can get a good overview of a polar bear population's ecology by following just a few animals intensively.
What are collars made of?
Soft, synthetic belting material that sheds water and ice. It is the same material used in conveyor belts during the processing of frozen foods—it stays flexible in cold temperatures but is strong enough that the bears can't easily tear them off.
What tracking system do you use?
Early collars were followed by aircraft via the VHF radio pulses they emitted. Later collars communicated directly with satellites via UHF. The most recent collars include a GPS–satellite-linked system—the same system your smart phone uses to tell you where you are when you are hiking or driving
At specified intervals each collared bear provides a position that is accurate to at least 10 meters (30 feet). The collar transmits this data to overhead satellites in batches—usually once a day. Some collars also store additional data for download upon retrieval.
How long does the battery in a collar last?
This depends on how much work scientists are asking the collar to do. Early VHF collars and even some of the first satellite collars could last for two years or more depending on how often they transmitted. More recent GPS collars do a lot more work and usually have a theoretical life of about 14 months. This means a collar could last long enough that a collar deployed in one spring capture season could still be operating in the capture season of the following year (most polar bear work is done in the late winter and spring when the ice is solid and the days are long). But collars can also fail and sometimes the bears remove them. So, if they last 12 months, scientists are pretty happy.
How do the collars come off?
Scientists always put collars on bears loosely enough that if a bear really wants to remove it, it can do so by pushing the collar over its head. But, the hope is that scientists will remove the collar when they recapture the bear.
In the last decade, automatic release systems were introduced and have been quickly improving. These allow collars to drop off a bear remotely and are pre-programmed for a set date. Some require line of sight (VHF) and the latest versions can theoretically be released via satellite link.
The basic and most reliable release mechanism has a clock, and scientists can set the day that they want it to drop off. They usually set the timer so that the collar will fall off shortly after the batteries are drained and the collar is no longer transmitting. That way, if they have not recaptured the bear and removed the collar, the bear is not forced to wear a collar that is no longer working. In addition to the timed release mechanism, the collars are attached with steel nuts and brass bolts. In a salt water environment, this system eventually corrodes and the collar will fall off even if the release mechanism fails. Failing that, the collar belting eventually will wear out and then drop off, but this takes longer and scientists try to not have collars on bears after they have stopped providing data.
Once they fall off, a VHF beacon allows researchers to find the collar, refit it with new batteries, and send it out again.
How many bears are collared each year?
This varies according to project goals, how well-funded a project is in a given year, and how successful scientists are in catching adult females. As examples, in 2009 collars were available for deployment in the following regions: 20 in the Beaufort Sea, 14 in Western Hudson Bay, and 16 in Foxe Basin.
What data do scientists collect?
Scientists collect location information, activity rates, and temperature data. Some collars record how much time a bear is spending in the water. Telemetry is one of the few means through which they can follow polar bears for long periods of time and determine their movements, habitat use, fidelity to areas, and the survival of offspring.
Have any bears died as a result of collars?
Scientists have no evidence that life-threatening injuries have occurred due to collaring from studies across the Arctic and over several decades. Researchers have observed hair loss under the collars and, on rare occasions, small to moderate abrasions or cuts behind the ears or on the neck. This has been most problematic in situations where bears become unnaturally obese from feeding on high calorie human-sourced food, like the remains of subsistence-harvested whales. Scientists are constantly vigilant for such problems and working to develop methods to avoid even minor injuries. The advent of collar release mechanisms added an excellent tool to the field kit, and biologists/engineers are continuously looking to improve collar design while also looking at alternative methods.
Scientists have never seen any evidence that collars interfere with natural movements or activities. Nor do data show any effects on reproduction or the survival of cubs. The collars only weigh two kilograms or so and the bears weigh over 200 kilograms, so at one percent of their weight or less, the collars are well below the point where they would have a significant mass.
What information is learned as a result of the collars?
Before we can estimate the size and trend of a population, we need to define the population. Only movement data, like those obtained from telemetry, can provide that definition for us. We can also determine hunting patterns, total distance moved, home range areas, habitat selection, how long bears may remain on land when the sea ice is absent, and when females enter and leave the dens where they have their cubs. We can also monitor the survival of offspring with a mother by locating her at intervals, with the aid of the VHF beacon on the collar.
What is the greatest benefit of the collars?
Scientists deploy collars randomly, and therefore can assume collared animals are representative of the population as a whole. Therefore, they provide a window into the movements and activities of the whole population. Following just a few animals intensively tells us a lot about all of the animals out there. These bears can provide much more information than just catching them once every few years during annual capture seasons. Importantly, as the sea ice declines due to global warming, collared bears show us how their movements and activities may be forced to change with the changing conditions. This may give us important advance information on the population crashes that are going to come if we do not reduce our greenhouse gas emissions—advance information that could serve as alarm bells to wildlife managers and policy makers.
What do you want people to know about the collars?
The collars provide us with a rare glimpse into the life of the bears that is much less invasive than trying to follow them out on the sea ice. There is no other practical means of learning about polar bears in winter when there is 24 hours of darkness.
We are able to gain insights important to understanding what is happening to the bears relative to climate warming, and to warn managers when we may be nearing critical thresholds beyond which could lead to population declines. By following a small number of bears, these animals can help us monitor how the whole population is faring. This data is critical to understanding the future for polar bears throughout the Arctic. By comparing many different areas, we are able to contrast changing ice conditions across the Arctic.
Without collaring and other population level research, we would not know what climate change is doing to the bears and the ecosystems of which they are a part. Without this information, we could easily see the bears start to slip away and only realize the extent of the problem after they are greatly reduced in range and abundance.
Despite the advances in telemetry and other research tools, it is important to remember that research will not protect polar bears unless the information we collect is used to guide managers and policy makers into leading the social changes we all need to make. Without dramatic reductions in our greenhouse gas emissions, telemetry and the detailed population understandings it provides only will allow us to become better polar bear historians.