A lot of what we talk about and report on is our female fishers. I suppose there are a lot of reasons for that but a major one is that we usually track our females and most of our males wear Argos transmitters produced for us by Sirtrack. The great thing about these transmitters is that we don’t have go out and do the tracking. The location is estimated through overhead satellites that transfer the data to a processing center that then sends it to us in our email – what some have dubbed “armchair biology”. One of the really important reasons we put these on males is because they allow us to track fishers over long distances.
Male fishers have big home ranges compared to females and they seem to cover a lot of area. Here, I have included a figure that shows data that we have collected on 4 males from the last 3 months (not all our males are included here). You can see from the points that they do a pretty good job of staying away from home ranges of other males even when when they share a common border and have some overlap. Just for fun I included a visual representation of a Kernel Density Estimator for female fishers. Basically, the darker colors are where female fishers are found the most. As you might expect there is a some overlap between males and females, but some males are somewhat off by themselves. It makes sense the the biggest most dominant males have home ranges that include more female’s home ranges, but we are still testing this hypothesis.
Yesterday Kevin described the frustration of not being able to find animals that “disappear”. The information we are getting from our Argos collars have been really informative with regards to showing us the fishers sometimes do seem to just go exploring. Just recently we have had two males that have seemed to wander away from their usual haunts. Had we been tracking these animals with regular VHF telemetry it is likely we would have just “lost” an animal for awhile until it eventually showed up again. We know females take these same types of trips, but I suspect we catch them in the act far less frequently.
If you look below at the two other figures I’ve included you can see male 1 and male 4 have each recently taken petty significant jaunts. Male 1 only recently set out toward the east. He has covered about 10 miles in the space of about a week. The other male made about a 20 miles round trip over the course of about a month. Notice that he wandered right through the middle of one of those dark red areas – the home range of one of our females released in year 2.
What do these trips represent for a male fisher? Well, that is another thing we are still thinking about. Maybe they are checking out locations of females. Particularly with the breeding season fast approaching it may be useful for males to keep track of potential mates. Perhaps they are simply looking for an area that has higher concentrations of prey or maybe, like ourselves, they just want to see some place new once in a while.