Posts Tagged With: dispersal

On the Road Again

For much of the spring and early summer, the job of tracking most of the female fishers isn’t all that difficult. Denning females spend a lot of time in their dens, so we usually have a specific point for starting our searches.  When they go out foraging, we know they will need to return to their den eventually, and often aren’t found too far away from these sites.

As we move into June and July, the kits grow quickly and become more mobile. The time spent in any one den becomes shorter, and females are out and about more and more. Keeping track of them starts to become more difficult. Once August rolls around, we often observe some larger movements, many of which take the females outside of the areas we have tracked them over the last many months.

This pattern of females making larger moves around this time is something we notice every year, but the reason is not fully known. Possibly, this has to do with them depleting the easy food sources closest to their dens, and these moves take them to better hunting grounds.

Another hypothesis for this move is that females are taking their kits to the edges (or outside) of their ranges to let them become familiar with an area for them to “disperse” to. Especially for any juvenile males, it is not advantageous for them to remain near their mom’s home range, so making a move to get the kits away from her range makes sense. Whatever the reason, it’s fun (although often frustrating) to track them in some different areas.

By now, the juveniles should be very close to dispersing (if they haven’t already) and being on their own. We will begin our trapping efforts in a few weeks, and it will be exciting to see if we can capture some of these youngsters, especially in the areas that we are seeing the adult females traveling to.


2015 VHF locations for 69940, a two year old denning female. Blue stars indicate locations from January until the middle of August.  At that point she took off to the southwest. Green stars show her locations from middle of August into the middle of September.

Juvenile fisher from the end of August. Getting big!

Photo of a juvenile fisher taken at the end of August. Getting big!

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The Grass Is Always Greener

One of the pleasant surprises during the fall trapping was recapturing an adult female, 1E003.  She wasn’t captured the previous fall, so it was the first chance we had to examine her since her release nearly two years ago.  Over the course of her time here, she has been a particularly challenging fisher to follow.  A brief history of this fishers’ time on the Stirling district:

During the spring of 2011, three months after being translocated, she denned and had kits over in the far eastern portion of our study area (at the time further east than any other females we were tracking).  This is a remote area of the district, and where she settled had fewer access roads than other areas.  We failed to capture her during the fall of 2011, but were able to catch a juvenile in her home range.  Through this past spring, we were still tracking her near her usual haunts on the eastern side of the district.  We found her in trees within 100m of each other on several days and believed she was about to den.  Then in mid-April, she vanished.  Her collars’ batteries were due to expire at any time, so we figured that was what had happened.  Thinking she had established a stable home range and would stay there, we weren’t expecting her to make any large movements.


Area covered during 1E003’s move from the east to the west.

Much to our surprise, during a June 2012 flight, we heard her signal again!  This time however, she was on the complete other side of the district. Given the distance from where we normally heard this signal, we were skeptical that this was indeed our fisher.  Instead, we thought it might be the transmitter of some other species associated with a project unknown to us.  For much of June and July we continued to track and estimate the locations of the animal, but we could never confirm that it was a fisher by visually identifying it. Shortly thereafter, the collar disappeared from the airwaves again and we were left wondering if this was actually her or not.  As mentioned above, we captured her during the trapping effort in November, indicating that she had probably been living in this new area, on the west side, since June.  Sometime between April and June she made a 25km trek (as the crow flies) across the district and set up shop in a new area.

IE003 denning area near burn

IE003 denning area near burn

Naturally, we were left wondering why an animal would make a huge move such as this.  Immediately after being released, translocated fishers often roam around for a couple of months before they settle in an area. Often, juveniles and adult males make large movements as well, but this is more uncommon for an adult female.

This eastern side of the district is much rockier than other areas of the study area, and was hit by a large fire a few years ago.  I remember being surprised the first time I went out there to look for her den that a fisher would settle in this area (you can see in the map the differences in the sides of the district).  It is possible that the pressure of denning and giving birth made her pick and stick to a place that wasn’t ideal.  Since she was released in January, she only had a couple of months to find a good place to den. She may have not had ample time to find the best possible place, and simply chose the best in the area she happened to be in.


1E003’s tracks from a few days ago.

The fact that she was able to survive, and likely raise kits, meant that she was getting enough food and other resources in the area.  However, it could be that with kits reaching adulthood there wasn’t enough to go around.  Possibly there was sufficient food, but maybe there was a paucity of mate choices (few males were known to frequent this area).  Fact is, we will probably never know exactly why she decided to pick up and leave an area she had occupied for over a year, or why she made such a long move instead of finding an area much closer.

Today, I was able to find her in a rest tree, about a mile from where she was re-trapped.  Since we captured her, we have been tracking her faithfully, and are starting to get a feel for the new areas she is using.  We know there are a few other female fishers right around her, so it will be interesting to see how she fits in.

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Fishers of the North Country

Well since I talked about female fishers yesterday I though it was only fair to give the males a little play today. Fortunately, one male in particular has given us some new and interesting things to talk about. First, a little background is in order.

As some of you might know in the first year of the translocation we had a male that almost immediately after release bolted north about 50 km near the town of Manton. He stayed in that area until his transmitter failed in June of 2010. Some recent photos from that area, just north of Shingletown, CA, indicate that this male is still in the area – though we have yet to recapture this animal to confirm. We grew to call this the “Manton male” for reasons that are hopefully apparent.

In year 2, the first male we released roamed quite a bit. As a matter of fact his satellite transmitter indicated that he was all the way into the central valley (not what we think of as typical fisher habitat) on at least one occasion in January of 2011. Unfortunately, we lost track of this fellow sometime in mid 2011 and we did not know where he had gone until the fall when we captured him near Manton (while we were trying to recapture the original Manton male). In the time since his capture he had not wandered that far from the capture area, and so it appear that this is now a big portion, if not the core, of his home range. So, in two years we had two males that found there way to roughly the same area. By the way, we have no indication that other fishers live in the area.

Okay, so now we are in year 3 of the translocation. Several new males have been released and they all stayed roughly in the areas where we released them. Well, until about 2 weeks ago anyway. On March 12 male 24315 suddenly moved about 15 km north. He then moved further north, you guessed it, to right around the Manton area. In the last several days he has moved another 15 km north of Manton! So, now we have three “Manton males”. I’ve included a couple of maps showing locations for all three of the males I’ve described. The first map is a larger scaled view and shows a good cross section of where we have located all three males. The second map is a closer view of just the northern locations and roughly centered on the Manton area. The second map also shows an approximate time line for male 24315 during the last 2 weeks.

The movements of these males are curious to me because they all went north and stopped or slowed down in the same area. We have had no males travel, and stay, south or east of their release locations though we might predict that we would observe this if males were striking off in random directions. So, why are are we seeing this apparent pattern of males traveling north? The short answer is “I don’t know”. Unfortunately, we still just don’t know enough about what sort of directional or environmental cues males might be using to guide them. Moreover, what resources or restrictions cause them to end up in the same general area is also unknown. The most logical answer is that there are female fishers in the area, but camera surveys in the area – conducted over the last two years – simply do not detect other non-collared fishers. It is possible that male 24315 will come back south. This is after all the breeding season and males have been known to travel a long way to find females. For now, I suppose why these males have traveled north will remain a mystery. So, “if you’re traveling in the north country fare” keep your eyes open and maybe you’ll be lucky enough to spot one of these males in their many travels.

Locations of three male fishers

Time series of male 24315's movements from March 12- March 28, 2012

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On The Road Again

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.

The locations for 4 selected males

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.

Male 1 recent movements

Male 4 recent movements

Categories: Updates | Tags: , , , , , , , , | 2 Comments

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