Posts Tagged With: reproduction

Growing Up Fisher

Over the last few months, many of the female fishers on Stirling have been busy raising their litters, and as such, we have been busy trying to keep track of them.  We see females start to den from mid-March to early-April, and try to document how many kits they end up having, along with what kind of structures they are using.  When we find a den, we put a few motion sensor cameras around it with the hope of capturing photos of kits when they move to a different den.  In addition to seeing kits, we sometimes get photos of other cool things like males visiting to breed, different prey being brought back to the dens, and visitation by predators.

Documenting kits is often a lesson in frustration and patience.  Fishers usually have multiple ways to get in/out of their dens, and many do a very good job of evading our cameras.  However, over the course of the summer, our persistence eventually paid off and we were able to document quite a number of kits from most of the known denning females!

From March 18th – July 15th, we documented 57 dens from 17 females.  We were able to confirm kits from 15 of 17 fishers.  Remote cameras placed around the dens picked up a minimum of 30 kits, for an average of 2 kits per female.  Like in previous years, the number of kits ranged from 1-3 per female.  The known rate of denning this year was 89%.

The length of stay in any one den varied greatly between individuals and dens.  We saw the first female move from a natal den on March 27th.  The last holdout stayed in her natal den until May 30th.  In contrast, one female had used 6 different dens before May 30th.

We often see mating behavior from late-March to early-April around dens, and this year was no exception.  Males visited the majority of early den sites, and cameras picked up breeding on multiple occasions.  In once instance, mating occurred over a 2 1/2 hour period!

Raising kits increases the energetic demand of fishers, who now have multiple mouths to feed.  Not surprisingly, we often see an increase in mortalities during the summer months from females raising young.  This summer we have had 3 females die who we knew were denning.  It is always sad when a fisher dies, and knowing that their kits will not make it is especially hard.  I usually reconcile this with the knowledge that we document a far greater number of kits than the number of fishers that die, and assuming many of these youngsters make it to adulthood, they should replace those we lost.

By this point in the summer, the juveniles are getting pretty big.  It won’t be too much longer before they disperse and try and make a living on their own.  Included are some pictures from this years’ denning.  I have tried to put them chronologically, so you can see the changes in kit size as the summer progresses.


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Young of the Year

It’s been nearly 3 months since we found our first dens of 2015, and we’ve been busy continuing to try and track females and get pictures of kits.  It hasn’t always been easy, and many of the females this year managed to move out of their natal dens unseen.  However, our persistence has finally been paying off over the past few weeks.  So far, we have confirmed a total of 19 kits from 11 denning females!  This averages to 1.7 kits per female, which is on par with what we have found in previous years. Mostly we’ve seen fishers with either 1 or 2 kits, although we did confirm a 3-kit litter from one female.

It’s enjoyable to me to see how fast the kits are growing. In just the last couple of weeks we have started to see some of the kits climbing down trees on their own, and playing around outside of dens (with adult supervision).  In some instances, the kits seem to be following mom to the new den instead of her carrying them.  It also appears from the photos that the females are starting to bring back more prey items to the dens.

At this point, it is very difficult to pin new maternal dens down. The females are out foraging the majority of the day, and since the kits are becoming more mobile it is probably easier for her to pack up and move to a new home.  There are still a couple of females from whom I think we have missed seeing a kit or two.  We will continue to opportunistically walk in on everyone to try and get as accurate of count as possible before the juveniles dispersal in the fall.

Below is a slideshow of many of the kits we have confirmed thus far. I have tried to put them chronologically so you can get an idea of just how fast these fishers are growing up. The first picture is from April 3rd, and the latest from June 8th.  Also, a camera from a log den found about a week ago captured hundreds of images of a female eating a squirrel while her kits were around! I put these into a slideshow you can watch HERE.

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All Eyes On Me

Throughout my career in wildlife work, I have had a number of awe-inspiring experiences.  Often, these are times when I’ve managed to catch a rare glimpse into the life of a wild animal.  While tracking fishers, I have had a few awesome encounters (many of which have been written about in previous blog posts).  A couple of weeks ago, I was fortunate enough to have two experiences back-to-back which I know will stick with me for the rest of my life.


A little blurry I know, but that’s 2 fishers!!

The first of these happened during a opportunistic walk in of fisher F8B8D.  This fisher was among the first group of fishers translocated to Stirling back in ’09-’10.  A few months after her release, her transmitter failed, and we were left wondering what happened to her.  To our delight last fall, we re-captured her!  Since that time we have been faithfully tracking her and learning what areas of the study area she has settled down in.

As the VHF signal grew stronger and I knew that I was getting close, I looked around at the nearby trees for any sign of her.  About 30ft up in a Douglas fir, I noticed a nest.  I’ve found fishers resting in nests many times before, so I moved upslope of the tree to get a better look.  Sure enough, I saw the tell-tale silhouette of a fisher head. I got my binoculars out, and to my surprise I found not one, but two fishers returning my stare from the nest!

The very next day I had a similar experience, only this time it was with a different fisher (36A8B, a two-year old).  This time as I got close, I looked up at a nest and again saw two fishers staring back at me.  As I was looking for a collar to try and identify who was who, 36A8B came into view from a higher branch, made her way down the tree, and briefly joined the two kits in the nest.  I was staring at three fishers!

It’s always very exciting to get a glimpse of a fisher.  Even though I often get fairly close to them while conducting radio telemetry, they are very hard to see, and are usually resting in the cavity of a tree or run away when I try to approach.  This is the first (and second) time in my many years of tracking to get to see a mother with her kit(s)!

Besides from just getting an awesome look at five fishers in two days, these two particular cases were also helpful for us. Both of these females were suspected to den this spring, but we were never able to confirm kits from them with remote cameras.  These visuals confirmed that they had reproduced this year, and have raised at least some of their offspring to this point!  By this time the kits are getting to be pretty large, with the juvenile males being about the same size as an adult female.  It won’t be too long now before the kits will disperse and be on their own.

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The Class of 2013

Over the last few weeks we have been observing many of the females moving from their natal dens to maternal ones, and just as we had hoped, some have had kits in tow!

The first fisher kind enough to show her kits this year was 714C2, a year-3 translocate.  This wasn’t too surprising to us on the ground, as this female seemed to constantly move dens last spring.  We recorded photos of her bringing two kits down the natal den tree.

The next three animals to move were all year-2 translocates.  Two of these, 21FB6 and 18871, have denned all three years since their release and we have documented kits from them each year!  93B5A, the oldest of the females we are currently tracking, just turned 8 years old!  This is also the third year she has denned on the Stirling district, and the second we have captured her kits on camera.  All three of these fishers have had a minimum of 2 kits each.

The last fisher that we found had moved from her natal den was 209DD, one of the females who was born on Stirling!  Her kits are the first we’ve confirmed from a fisher native to this district!  It appears she has also had a minimum of 2 kits, however the second picture isn’t as clear as we would like.

We have a couple of females that are still using their natal dens.  The amount of time a fisher will remain in the natal den seems to vary wildly from individual to individual and year to year, so its hard to tell when they will make a move to another den.  As is to be expected, a couple of the females managed to move their kits into maternal dens without being detected by the remote cameras.  Hopefully during their next move we will get some pics of them.  Until then, enjoy some photos of the kits we’ve seen so far!

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Love is in the Air

Okay, so maybe love isn’t the best choice of words.

The other day I was searching for the natal den of one of our trans-located females.  Having narrowed the signal down, I thought I knew where I needed to go in order to find her.  As I was riding on the ATV past an old road, I caught a “fisher log” out of the corner of my eye.  Now I often see fisher shaped rocks and logs, and 99 times out of 100 they are just that.  This time however, as I backed up to get another look, this particular log turned around and loped off!

I quickly grabbed my gear and started walking after the fisher, thinking it was probably the female I was looking for.  As I walked a ways down the road I realized that although I was extremely close to the female, her signal indicated that she was not moving.  Just then, one of the Argos collared males appeared and started to approach me!  He got about 15 feet away, then moved up-slope towards a large tanoak.  After sniffing around the base of the tree for a few seconds he slowly walked off.  Not surprisingly, this turned out to be the tree the female was in!  This was the first time I have personally spotted a male at a den (although it isn’t too uncommon among the field crew, and our cameras detect it frequently).  It was certainly nice of him to lead me to the tree she was in.

The spring denning time coincides with the breeding season for fishers.  For us on the ground, it is probably one of the best opportunities to spot the males out in the woods.  Males are busy seeking out the females, and just like in this case, often end up at their dens.  I put up a camera pointing at the tree, and it caught a cool series of pictures.


The male in the picture is not the male that led me to the den.  He is un-collared, and appears to be quite a bit smaller than the one I saw there.  It wouldn’t surprise me to catch some larger males visiting the den in the next few days.  This particular female has been in the same tree for a few days now, indicating this this is probably her den.  We are starting to see many of the females we are tracking settling into denning behavior, but more on this in a few days!


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To Den Or Not To Den?

That is the question. That time of year is rapidly approaching once again, expectant mothers on and around Stirling will soon have to pick their spot and settle down to the task of raising kits. The den season, particularly the early rush to pinpoint natal dens (those in which a female gives birth as opposed to the maternal dens she will use later in the season) is one of our busiest periods on the ground and from a personal perspective, one of the more rewarding.

This will be the fourth season in which Fishers have denned on Stirling since the reintroduction began and again it offers some potential milestones for the project. We have already seen the birth of the first kits sired on the district, the one to watch out for this season is the potential to confirm the first litters born to females native to the district. Although it is very possible that this happened last year we were not actively tracking any females born on Stirling who were potentially reproductive during the 2012 den season. Currently we are tracking 4 such animals and barring any mishaps we expect to locate natal dens for each of them should they give birth this season.

From the table below you can see that this year we are tracking 11 females which we believe could reproduce. Besides the 4 animals mentioned previously we have 5 year 2 translocates, all of which have produced kits previously and 2 year 3 translocates, only one of which has reproduced before.


Females with the potential to reproduce in 2013

As a point of comparison, ahead of the 2012 season we were tracking 10 potentially reproductive females, consisting of a spread of year 2 and year 3 translocates. Ultimately we confirmed natal dens for each one of these animals.

There is also a slight possibility that some of the 4 females we caught in the fall of 2012 and deemed to have been born that spring were actually born in 2011 and would therefore be able to reproduce this year. So, although we think this unlikely we will have to keep a close eye on what these animals are doing to be sure we don’t miss anything.

Doubtless you will see more from us as we start confirming dens and setting remote cameras. Over the first 3 years we have seen the den season really start to kickoff in late March with our median date of den confirmation (this date can sometimes be a day or 2 later than the kits actual date of birth) being March 30th. The majority of dens are generally found within a week or so around this date although our data shows a spread of about a month for the population as a whole. Our earliest record thus far is March 17th, only 1 week away!

Here is something you’ve seen before to whet your appetites.


Hopefully new pictures will follow in the next month!


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We recently got confirmation of the first kits of 2012, as a couple of female fishers moved their dens!  Although we suspect that nine of the females we are tracking have denned and had kits, it’s nice to get some actual photos of them.

93B5A’s kit.

The first of the year belonged to female 93B5A, who was released in the fall of 2010.  This is exciting because even though she did appear to den last year, we never got any pictures of her kits.  The picture was taken only two weeks after we found her den, and as you can see the kit is pretty small.

The most recent picture of a kit came from fisher 20058, an animal that was released last fall.  This kit appears to be larger, which isn’t surprising as it was moved six weeks after we first suspected she had denned.  It is interesting to see how fast the kits are growing at this stage.

We only captured one kit on camera for each female, but it wouldn’t be at all surprising to learn that they have more.  Although the cameras we use are pretty good, fishers have a habit of getting around without triggering them.  In the case of 93B5A, she returned to the den tree shortly after moving one kit, but the camera didn’t detect her coming back down again.


20058’s kit, another view.

20058’s kit.

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The Secret Lives of Fishers

A couple of our remote cameras captured a rarely seen fisher behavior a few days ago.  Check it out:















They’re a little grainy, but the top two pictures show two fishers coming down the tree, while in the bottom two they appear to be mating at the base. These cameras were pointed at the suspected natal den tree of fisher 18871.  Many of our cameras at den trees have captured males coming and going, but to actually see them mating is pretty rare.



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DENizens of the Trees

In the last 2 weeks we have managed to confirm that at least 5 of our females have settled into patterns consistent with denning behavior. We detected the first on about March 21 and that is the earliest we have detected a female in a den over the last 3 seasons (more on that  later). Three of the females were released in year 2 of the translocation. One of those females did not den last year and 2 did. The other females were those released in year 3. This is positive because it shows that the females from last year found mates and appear to have had kits. We demonstrated this last year with first year animals, but observing it for the second year adds data and understanding to important population processes. Matt observed a male fisher at female 1F111’s den tree already this year. This was a female released in year 3  and the den is about 11 km east of where we released her. I am still amazed that males show up at den trees seemingly right after females establish them, but since that is a male fishers specialty I guess I shouldn’t be surprised at all.

Black oak den tree

The dens are spread across a big swath of the district. From the west side in the Big Chico Creek Drainage to the east side near highway 70. We even have one female denning on the north side of Deer Creek. We still have a lot of females that have yet to den so it should be interesting to see the distribution of their dens when all is said and done.

Den tree (on right) of female 1F111

The first two years of the project  the earliest we ever found a den was March 23 and most were found after April 1. This year we have found 3 dens before March 23 and another 2 before the 26th, One reason for this might be that we have better access to where females are because we have had relatively little snow accumulate over the winter. The last two years we were snowmobiling/snowshoeing into dens through much of April. Alternatively, the relatively mild winter might have simply allowed females to den a little bit earlier (some anyway) because they were in a better condition. At least three of these females appear to have never given birth before (based on past tracking and physical examination), and this could influence their body condition and timing of birth. All of this is speculation of course, and the bulk of females have yet to den so we might just be observing natural variation in timing of births. It will be interesting to see if other studies detect earlier than usual denning behavior.

We’ll be putting cameras on all the den trees we find to document when females move their litters to maternal dens and to make minimum estimates of their litters sizes. More information to come….

A view of the area immediately adjacent to a fisher den

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