Author Archives: aaronfacka

Timing is important

I thought I would share a link to our recently published paper in the journal Ecosphere. See the paper at this link.  In this paper we collaborated with the good folks of the Olympic Peninsula  fisher reintroduction to demonstrate that when we release a female is important toward her short term reproductive success.

In addition to showing some interesting biology on fishers I think the paper shows the power of collaborative efforts between projects. Thanks to all the folks from Washington for all their help and support on this paper as well as to Roger and Richard for their help in writing it.


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Hair-raising adventures

Over the past six months I have cleaned and analyzed over 400 samples of fisher scat that had been collected during trapping events, den trees and walkins from 2009 to 2013. While being a scat analyst has not been the most glamorous job, I found the work to be extremely interesting as well as informative.  I completed this work in the Biodiversity Lab at the North Carolina Museum of Natural Science’s Nature Research Center (special thanks to Roland Kays).  Before I was able to start going through the samples, I had to create a reference collection of animals that were likely a part of a fisher’s diet potential prey animals (like porcupines – see picture).


Porcupines – making people happy

This gave me the opportunity to explore the full collection of mammals at the museum and take hair samples from those species. With these samples I made slides that demonstrated the cuticle and medulla for each species.

This allowed me to compare hairs found within the scat samples to hairs from known samples of identified animals.  In order to identify what the fishers had eaten, I first had to clean the samples.  The washing machine in the lab was not able to sufficient to separate and clean the samples so I had to clean each one manually.  The rest of the lab was not very fond of cleaning days; as you can imagine opening and handling scat that had been frozen for a year or longer does not smell like flowers.  I had two metal wash drums with different sized grates and a soft fine mesh lining in a sink with a tube attached to the faucet.  For each sample I would place 90% of the scat onto the first drum and leave the remaining in the bag to be used for hormone analysis.   From there I would run water over the sample to filter it through the grates and clean all the feces off of it.


Washing samples

Remaining particles that couldn’t pass through the drum would be moved onto a plate and I would repeat the process on the second drum and then again on the fine mesh.  Once a sample had been completely cleaned and all the remaining particles were separated onto a labeled plate it was put into a dryer. After about a day the samples would be dry and the analysis began.  Hair identification can be a grueling but fun process. Species within the same family, for example squirrels (Sciuridae), all have very similar medulla and cuticle patterns. Therefore, it is important to be able to identify the small differences.  For instance, normal guard hairs for the western Gray Squirrel (Sciurus griseus) are black with a single white band near the center of the shaft with significant kinks throughout, whereas the hair for the California ground squirrel (Spermophilus beechyi) is black with a single white band slightly closer to the tip and less kinks.  If I was not able to identify a hair by using a dissecting microscope I would create a slide with the unknown hair and place it under the compound microscope to see and compare the cuticle scale pattern and medulla pattern within the hair. Along with hair identification I was able to determine a prey species by remnants of tooth and bone as well as scales, feathers, or exoskeleton.  Most often I found evidence of various species of rodents (especially squirrels), but there were other interesting things fishers ate. For example, one fisher in particular had consumed common wasps (Vespula vulgaris) on multiple occasions.  These samples were very intriguing since the wasps were still in tact.

he data I compiled will be used to continue learning more about the diet of fishers and hopefully identify habitats with available prey.

~Kyra Pruitt currently attends NCSU and serves as one of the many excellent technicians doing great work on the fisher translocation project.





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A better mouse trapper

Fishers, like most mustelids, are predators. Unfortunately, the food available to them versus what they kill and eat are often unknown to researchers. We have dedicated a good chunk of our summer trying to understand better what is available for fishers to eat compared with what they actually select on our study site. This summer we had several folks out trapping and documenting potential prey species for fishers across the Stirling district. Many people were involved but we had three excellent field crew out there doing most of the work. Alex, Erika, and Jesse (see their lovely photos below) were out most days setting and checking traps in diverse types of cover and tree stand types. The point of all this is to attempt to understand where specific types of prey are found on the landscape based on differences in the environment and forest management practices.

We are just starting to examine these data to document and explore specific patterns of occupancy and distribution for different prey species. Nevertheless, we encountered many different species of mammals, birds, and herpetofauna (snakes and lizards mostly) across the landscape thru the summer. We captured deer mice (Peromyscus spp.) just about anywhere we set traps, and woodrats (Neotoma spp) also occupy diverse land covers types. We do not catch them as often as deer mice, but they are still abundant. The crew also captured ground squirrels (Otospermophilus beechyii), Douglas squirrels (Tamiasciurus douglasii), various chipmunks, and even hapless ringtail (Bassariscus astutus). While setting and checking traps they also kept an eye out for lizards and snakes. A few of the snakes were of the venomous variety (rattlesnakes) as well as snakes that are not quite so dangerous but just as cool. Alligator lizards and fence lizards also seem to be in lots of places as well. Other types of potential prey species like gray squirrels, black-tailed jack rabbits and flying squirrels were also noted but seem to be harder to capture in live-traps.

Of course, when you put a lot of fresh peanut butter and oats out in a forest you get other critters that are interested. Bears are a common visitor and they are usually unconcerned with maintaining the integrity of our trapping grids. They move, turnover, often destroy, and at other times even steal traps! Bears are one of our nemeses both when doing this kind of work and just about everything else (they are everywhere). We also see foxes and occasionally we even see a fisher wander across a trapping grid.

The crew is primarily taking data on where we capture specific types of animals. They also document the sex and relative age of each species, measure the weight, examine them for ectoparasites and  give them marks and tags so we can document which individuals we have recaptured. We are also collaborating with Deana Clifford and the Wildlife Investigations Lab to evaluate some captured animals for rodenticides and diseases. All these data are important to future analyses and monitoring.

Vegetation types are also important and we

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collect information on the number of trees and shrubs that occur on each trapping grid. Sometimes the crew accidently document other species of plants. They often don’t’ know this until a day or two later when they realize they have a poison oak rash and then must bear the burden of scratching and itching for several days. It’s a badge of honor. We all wear it proudly at one point or another – except for those people lucky enough not to be affected (we are all looking at you Jesse) – if not without a large degree of annoyance.

Good times were had by all and more importantly we have collected new and interesting information that will help us conserve and manage fishers and fisher forests.

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On this day

Today (December 9th) is a special day for me. Five years ago today I recall walking down a snow covered mountain road holding one end of a wooden box that contained a fisher. Holding the other end of that box was Roger and right beside us walked Richard and Scott – also holding the ends of a box the held a fisher. Our destination was a small clearing in the forest where many of our friends, colleagues, and even members of the media awaited us. More precisely, they waited for the fishers. The two female fishers we carried in those boxes would be the first 2 fishers released as part of our translocation project onto the Stirling district. We placed the boxes near the edge of the clearing and opened the doors and waited, and then we waited a little more. All the humans eagerly waited for the fishers to emerge from those boxes, but the fishers had other ideas. I can’t say I blame them. Having a bunch of beady-eyed humans looking at you can’t be a fun situation for a fisher (or any other creature either I imagine). I suspect we all, especially the members of the media, had a great illusion that the fishers would emerge promptly and slowly, pose for a few pictures, and then saunter away at a leisurely pace while we snapped pictures and looked on in awe. The reality was quite the opposite as both fishers, in their turn, streaked out of their boxes as a flash of brown into this new place they we hoped they could make into a home. Seeing the fishers run off gave a sense of great accomplishment and wonder but also of great responsibility and future hard work. I suppose Scott provided the most sobering perspective of the day (to me anyway) when he simply said “There are now fishers in the northern Sierra”. Yep, there sure were and that meant that we had to keep track of them, study them and also move an additional 38 fishers over the next 2 years.

Hill releasing fisher

Releasing a male fisher in December 2009


Female fisher looking out of release box

Two years later on December 9th I was once again standing in a big circle of people waiting for fishers to come out of wooden boxes. Once again the media (see link for one article and some pictures) was there as well as friends and collaborators of the project. The outcome was much the same as fishers sat in the boxes refusing to leave and when they finally did they fled with extreme expediency. We released 2 females and 1 male, and they would be the last of the fishers translocated to Stirling. Not all the releases were met with media attention or lots of people milling around waiting to take pictures. In fact, most fishers were released with just 1 or 2 people looking on and waiting. Personally, I prefer a small release entourage. In all cases, the releases were the easiest part of the whole process.

It might take me an entire book to write about the tremendous effort that it took to get fishers to Stirling. There are myriad stories about trapping, handling, and transporting fishers. There are just as many about long meetings and phone calls where we considered all the risks and benefits and tried to decide the best course of action, and for each story I have the rest of our team might have 20 more. Yet, all those stories and experiences would only tell a small part of the entire story, because there were literally years of planning and discussion that went into developing and creating the project and the collaborations that made it all work. Most of that happening long before I ever even knew about the project. So, while I consider December 9th the birthday of the project we should always remember that it had a very long gestation as well, and that process went without fanfare or appreciation. The days we released fishers, and how those days came to be, are only one part, and perhaps the least important part, of what our project is all about.


Some of the team handling a fisher before release

transport boxes in truck

Transport boxes full of fishers heading to Stirling

On December 10th, 2009, a day after we released the first fishers, Roger and I set out to find them. It was a mixed bag as we found one female within 1 km of the release point and had no luck finding the other. It took a few days, a few weeks actually, but we eventually found the other female. We tracked both of these females, as well as 7 other released in late December and January of 2010, throughout the spring. Both those two females survived and produced kits the first year as did most of the other females we tracked. Since that day we have spent nearly every day for 5 years looking for fishers to understand the specifics of how and where they live and reproduce. Of course, “we” isn’t Roger and I anymore. “We” is now a large number of folks that work, and have worked, in the field collecting data, and without them the project would not continue. It is also all the people behind the scenes and behind desks and telephones, in front of computers, in laboratories, and in many places and roles that make the project continue to work. The project would have failed a long time ago without all those many people and they all deserve a great deal of gratitude and appreciation. We continue looking for fishers and learning about their lives and ability to survive and reproduce on a landscape managed primarily for timber production. We don’t know everything, obviously, and though we’ve made great strides more information, time, and thinking is needed to fully understand the dynamics that drive fisher populations on Stirling. Nevertheless, five years later we know that there are STILL fishers in the northern Sierra Nevada.

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Getting the Point

Getting the Point            

October is long gone and the shortening days of November signal that fall trapping is coming to a close. Unfortunately, we have not been able to update all of you with the happenings as much as we’d like, but I suspect we’ll be putting out more posts in the coming weeks.

One of the parts of trapping, and handling fishers, that I most anticipate is in the moments after we’ve sedated a fisher and get to physically examine it for the first time. One of the first priorities is to  see if it has any major wounds or ailments that need immediate attention or that give us concern. Recently, while examining a female fisher (captured on Stirling in the fall of 2012) we noticed that there was something odd about the area around her right shoulder and neck. Not coincidentally Roger and Kevin both spotted the same thing when I did and all three of us were looking on at several very large, stiff, and prominent hairs jutting from the fisher. I found myself thinking ‘those don’t look like fisher hairs, and I wonder what they are?”. Kevin and Roger were apparently thinking the same thing and nearly in unison we shouted “PORCUPINE!”. A little further examination confirmed our suspicions. Three porcupine quills were embedded in the young female’s right shoulder suggesting she had an encounter with porcupine in the not too distant past.


Close up of 3 porcupine quills in right shoulder of female fisher captured on Stirling in 2014


Female fisher with porcupine quills in right shoulder

Perhaps you are wondering why such a fuss about a few porcupines quills? Well, there are a few reasons that this got us excited, but mainly it was because we have never found a fisher on Stirling with porcupine quills. The discovery is significant because fishers are one of the few consistent predators on the spike-laden rodents when they occur together. As  you probably know, or can deduce, porcupines have all those spikes as more than just a bold fashion statement – they offer pretty good protection from most predators (view a recent video of an African porcupine vs lions). Fishers are uniquely adapted to capture and kill porcupines and they may have an important role in regulating porcupine populations in some areas. Porcupines are large relative to other prey fishers catch and kill (e.g., squirrels and hares) and they provide a large source of energy to fishers (read this if you want to learn more). We have never documented porcupines on Stirling, since we’ve released fishers, and this suggests that porcupines are rare. Having porcupines and fishers on Stirling at the same time might alter the dynamics of how and where fishers forage, their home ranges size and structure, and even their population dynamics.


Porcupine (Erethizon dorsatum)

We don’t know if our female fisher actually killed a porcupine, but she certainly ran across one and we have a pretty good idea of the places she likes to hang out in. For now, it is only a fun little anecdote about one of the fishers on Stirling. Nevertheless, it is an exciting story and perhaps the first in a series of important observations. Such information is one of the reasons we endure a long trapping season and why we subject animals to the burden and stress of capture. Ultimately, it is all important information about what fishers are doing and how their daily lives translate into their ability to persist.


Depiction of a fisher capturing a porcupine (painted by Consie Powell)


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The Most Wonderful Time of the Year

Yes, I know the saying is generally reserved for a little later in the year, but that only applies to people who haven’t had the pleasure of trapping fishers in the fall. For those of us that have, and are about to again, the fall trapping season really is a marvelous time to be alive and doing field work. October 13th marked the beginning of our annual large-scale trapping and population monitoring effort on the Stirling district. Some have called this hectic rush to capture fishers the ‘fisher-palooza’, the ‘trapping blitz’ and sometimes just ‘fall trapping’, but I’ve always been fond of the term “Fisher Frenzy”. For those of you that have experienced it you’ll understand why I prefer this term — it really is a month-long frenzy. It is extremely enjoyable to set traps, capture and process fishers but it is always a grueling period where everyone is constantly busy and slightly stressed about everything that is going on.

On a daily basis we are deploying, checking, baiting, and hauling over 100 traps scattered across much of the study site. This may not seem all that bad except that it is critical that we check each and every trap once a day, at a minimum, and it takes a lot of thought and planning to make sure that we get this done. Each trap is usually about 1 mile from another and it can take 1 person half a day to check just 20 traps. In addition to fishers we catch foxes, ringtails, opossums, raccoon, and the bears are always investigating, rolling, and sometimes damaging traps too. If it snows or rains then that adds to both our comfort levels (have you ever spent all day checking traps on an ATV in the rain?) as well as the possibility we will not be able to get into our trap sites easily. The field crew (led by the intrepid Kevin Smith) has spent weeks fixing traps, finding locations, getting bait, and organizing routes and people. So, you can imagine they are already a probably a little stressed and maybe even sleep deprived, but they are doing an outstanding job.

I suppose I have’t made the experience sound all that wonderful to this point, but the reality is all the preparation and the daily grind is a very small price to pay for the experience and information we get from the fall trapping effort. Trapping fishers allows us to see, and examine, fishers that have been out on the landscape for the last year (or longer) and evaluate how well they are doing. It also introduces us to new fishers that have been born on Stirling and to get information on their condition, age, reproductive status, parasites as well as genetically identifying them. From the trapping data we can evaluate how much the population has grown, or shrank, and we can collar new animals so we can continue to track them.  So, we learn a lot about the fishers, and the experience is a great time as well. Being out in the woods and setting and checking traps is, at least for me, one of my favorite things about field work and I enjoy the experience immensely. It is also a time when the different members of our team get to be around each other and work together for a common purpose. We learn a lot and generally have a great time. So, as you read this some member of the crew might be leaning over a closed trap and hearing the muffled chuckle that a trapped fishers makes and seeing those lovely green eyes staring back at them from the trap. We should all be so lucky! With luck we’ll be able to keep everyone up to date on our trapping success over the next few weeks.

I’m enjoying myself like a kid at Christmas with a bunch of presents that are sitting out in the woods just waiting to be unwrapped. Indeed, it is the most wonderful time of the year.


Categories: Field Day

Warm winter nights….and happy endings.

When you wake up in the morning, you never really know what the day is going to have in store for you.  We do, after all, carve out our niche in the world by following the daily habits of small furry critters in a predominantly wild landscape.  We often grow attached to our fuzzy wards (how could we not?).  So when something in our data collection portends trouble for one of them, we mobilize to see what we can do.

Males that we capture and deem healthy enough to carry the weight sport ARGOS collars.  These collars communicate with orbiting satellites to determine the collar’s location and the satellites then relay location information via email right to my laptop.

There’s me in the corner!

Armchair biology.  Technology!  While this sounds like a road to obsolescence for field biologists, we still need to track the collar (and fisher) down when the data tells us something is amiss.  The collars are only on during certain times each day, and during this window the collar transmits once a minute to the satellites.  We’ve got a nifty receiver that lets us track it down via strength of the signal and distance from the collar as it transmits.

Male 190 was released in December 2011, and has been with us a little while.  He’s often seen at female den trees during mating season, and all in all, he’s just a sturdy, well built fellow.  It was distressing, therefore, to see some of the data from his collar suggest that he might no longer be with us.  To figure out if 190 was ok Julie and I looked into when the collar transmits and, lucky for us (sarcasm), it transmits from 5PM – 9PM and again from 1AM-5AM.  With the weather being wet as it has been for a time, we knew it was going to be an interesting hunt.  Just what we enjoy, if you can believe it.  We hoped for a dropped collar, and tried not to think about finding a carcass.  It was wet, getting dark, and we were heading into uncertain terrain.

Andria volunteered to go out hunting with me.  With the rain and the wet muddy roads, going in by truck was out of the question. Not to mention our only access was a long and partially closed road that would have required chainsaws, and more time (and daylight) than we could afford.  So ATVs were on the menu.  We knew the area we were headed to, and had a rough route planned (no one had visited this area since the rain, so all routes are tentative).  After dropping the trucks and heading out on the ATVs we began hearing the signal we had hoped for.  We continued on our pre-planned route, as a time or two doing this has taught me that signals broadcast up from a creek bottom can give misleading readings from a ridge top.  Along the way we had to move downed trees and rocks.

After getting all the way down to where our most recent data suggested 190 may be, we could hear no signals from the collar.  This had me daring to think that maybe, just maybe, he’s still alive – but somewhere other than where the recent points told us he might be.  We rushed as best we could back to the top of the ridge and posted up for a few minutes.  Lo and Behold, the signal boomed in to our receiver and continued to change in direction and intensity, quite quickly.  He was not far from where we randomly stopped, doing his thing and probably oblivious to our racket!  

Relief.   Elation.  High fives.  Back to the truck.  We were able to get out there, nose about, and determine that this guy is still hanging around, though probably weathering the worst of the rain in a tree hole somewhere, shielding the collar from reaching the satellites.  A good nights work, and home before 10PM.


UPDATE 2/15/2014:  Activity data from collar came through tonight and shows good readings across the board.  Sweet.

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“What’s past is prologue”

For those of you not aware, our annual fall trapping effort on Stirling has been underway for several weeks now and we are getting lots of exciting results. Probably the most exciting, at least for me, is that we recently captured a female (ID: F8B8D) that we released in year 1 (2009-2010) of the project. Capturing this important for a number of reasons and I’ll explain those reasons a bit better a little further along. First, I wanted to give a little history on this female to give some context for why her recent capture in important.

Fisher F8B8D in the fall of 2013 (top) and the in january of 2010 (bottom). We photograph the undersides of all fishers to describe and identify their unique patterns of markings. If you look closely you can tell this is the same fisher by examining her pattern of white blazes.

Fisher F8B8D in the fall of 2013 (top) and the in january of 2010 (bottom). We photograph the undersides of all fishers to describe and identify their unique patterns of markings. If you look closely you can tell this is the same fisher by examining her pattern of white blazes.

Female F8B8D was captured in January of 2010 north of highway 299 and between Shasta and Trinity lakes. We deemed her a good candidate for translocation to Stirling because she appeared to have reproduced in the past and she was in good physical condition suggesting she was mature and good handle the stresses of being hauled off to a new landscape. Like all females in the first year of the translocation she was implanted with a VHF transmitter so that we could track her movements. After she cleared our disease protocols we translocated her to Stirling on January 10th and released her in a tributary of Butte Creek near where most of our year-1 fishers were released. I can tell you she didn’t stay there for very long and the next day I found her on the east side of the ridge in the West Branch of the Feather River. For the next 6 months we often found her on the ridge between these two drainages (see the map of her 2010 home range). Unfortunately, we could never confirm that she had kits, because she never stayed in a den tree for very long. We suspect this may have something to do with the timing of when she was released, but that is another story. In the middle part of the summer F8B8D started moving south towards Stirling city and in fact the final time we found her signal in 2010 she was just to the east of Stirling city. Unfortunately, we were never able to find her signal again and all indications were that the transmitter had failed in early August of 2010.

on the left is veterinarian extraordinaire Diana Clifford, along with ANF, examining fisher F8B8D prior to surgery to surgically implant a VHF transmitter on the right.

on the left is veterinarian extraordinaire Diana Clifford, along with ANF, examining fisher F8B8D prior to surgery to surgically implant a VHF transmitter on the right.




Estimated home range (black lines) of female F8B8D in 2010 as well as the location of her original release site (red star), last known location in 2010 (blue circle) and both recapture locations in the fall of 2013 (red circles). The green line is the access road used for setting and retrieving those traps.

Estimated home range (black lines) of female F8B8D in 2010 as well as the location of her original release site (red star), last known location in 2010 (blue circle) and both recapture locations in the fall of 2013 (red circles). The green line is the access road used for setting and retrieving those traps.

Since we lost track of F8B8D in 2010 I’ve often wondered about what became of her. Each time we’ve trapped she has been a female that I’ve specifically thought about and tried to places traps in her former home range and in places I thought she might have settled into. We never had any success catching her and frankly we’ve had very poor success trapping any female that we released in that first year. In fact, up until this fall we had only recaptured 1 other female from the year-1 cohort and that was back in the spring of 2011. In truth, I had resigned myself to the idea that those females were all dead or were just of the disposition to never be captured again. Of course, not knowing which of those two possibilities were true was a problem because we it left us without important information.

The recapture of F8B8D helps to answer a few of those questions. Or, at the least it gives us insight into what the truth really is. Most importantly, we know that some (at least one) females that were released in year 1 are still alive. Maybe there are more out there living in places that we released them and hopefully giving birth to new fishers that will help to maintain our young population. Now that F8B8D has been recaptured (twice now actually) and collared we can see what her current home range looks like and how it compares to the areas she was using in 2010. We can also see how other fishers have been responding to her current home range by studying their space-use in relationship to hers even while she went untracked. F8B8D was recaptured not too far from the last place we tracked her and so perhaps she has been living in that same area this entire time. We also learned that the implants that we gave these females can remain in them and have relatively little impact on them. Upon removal the transmitter was still intact and doesn’t appear to have done any internal damage. F8B8D was about the same body mass and condition as when we released her and that suggests that she has been making a reasonable living for herself since we released her. Based on her teat size we also think that F8B8D likely had kits in the past year and this demonstrates that the year-1 females are not only living but also reproducing. Now, it’s possible that this is the only year-1 female still alive, and we just don’t’ know for sure, but it is a positive sign.

The underside of Fisher F8B8D showing large teats, indicative of a female that gave birth in the past year. Note that her belly has been shaved so that the implanted transmitter can be surgically removed.

The underside of Fisher F8B8D showing large teats, indicative of a female that gave birth in the past year. Note that her belly has been shaved so that the implanted transmitter can be surgically removed.





Fisher F8B8D in a transportation box after surgery to remove her implant. She was also fit with a new collar, re-vaccinated for rabies and canine distemper, and her general condition assessed. Fishers can be released back into the wild  within a few hours after surgery without any obvious impacts to their well being or behavior.

Fisher F8B8D in a transportation box after surgery to remove her implant. She was also fit with a new collar, re-vaccinated for rabies and canine distemper, and her general condition assessed. Fishers can be released back into the wild within a few hours after surgery without any obvious impacts to their well being or long-term behavior.


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We Report

Some of you out there may remember when we did blog style posts on the California  Department of Fish and Game (now Fish and Wildlife) website. During that period we called the section “Notes from the Field”. In late 2011 we decided that that an actual blog would be a better way of approaching updating folks about what we were doing, and in general I think that has worked out pretty well. Unfortunately, we then stopped posting regular updates to the departmental website and it quickly became dated. Recently, we decided to just get rid of the “Notes from the Field” (some of you have recently gone looking for it and found out  it doesn’t exist) section and use the departmental website  for holding and sharing documents, presentation, and other more formal information about the project.

We recently posted our 2011 annual report to the site and it can be found in the “Project  Updates” section or simply along the left hand side of the page under “Project Documents”.  You may ask yourself why we are just getting around to posting a 2011 report given that it’s already 2013. Well, the truth is we fell a little behind on this document and we only just finalized it a few weeks ago. In any case it is there now and hopefully it has some interesting and useful information about the project up until the end of 2011. We are currently hard at work on the 2012 annual report and we are committed to getting that finalized within the next month. At which time we’ll post it as well.

In the meantime keep coming to the blog for updates about the daily happenings in fisher land (our portion of it anyway).

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All About The Numbers

How many are there? That may be the most asked question in the history of ecology and wildlife management (at least one of them). Unfortunately, it is not an easy question to answer with any certainty. Animals don’t line up and volunteer to be counted, and thus biologists must find ways to estimate population sizes rather than having absolute and verifiable counts. Many hours of research (link) and multiple volumes (link) have gone into designing and describing ways of estimating populations sizes, and there are still many unsolved problems that are being worked on all the time.

Estimating population size for animals like fishers is difficult because they are relatively rare and spread over large areas that may be difficult to access and survey. Trapping is one method that we can use to make estimates of fisher population sizes using mark-recapture techniques. Additionally, trapping gives us insight into the sexes and ages of the animals what we capture. Because we attempt to survey as much of the area where fishers might live as we can it requires a lot of traps spread out over a big area (see the map below). It’s a busy time and a bit frenzied (hence “Fisher Frenzy”).

Map showing distribution of traps that captured (red dots) and did not capture (blue dots) captures during fall of 2012

Map showing distribution of traps that captured (red dots) and did not capture (blue dots) fishers during fall of 2012

Kevin gave some basic counts of the animals we captured but I thought I would provide a little more detail about the trapping, and some of the implications of the results. Of the 29 fishers we captured 14 were males and 15 were females. The majority of animals we captured were animals that were born on Stirling and that we estimate at 6-19 months old. You can see the percent of animals that we captured from each cohort in the top panel of the figure below. Though we captured more young animals there are still substantial number of adult animals from each of the first 3 years of the translocation. To date, we can confirm that 11 translocated fishers have died, and a minimum of 23 animals were born on Stirling – a net gain of 12. Unfortunately  we do not know the fates of 14 translocated fishers (lost collars etc) meaning that some, or all, could have died. Still, the number of  young fishers we’ve captured is nearly the same as all translocated animals that died or have gone missing.

Percent of fishers captured (top panel) and percent of the known alive population (bottom) by their release or capture cohort

Percent of fishers captured (top panel) and percent of the known alive population (bottom) by their release or capture cohort. Juv 2011 and 2012 are those animals less then 2 years old born on Stirling and capture in those respective years. AdY1, AdY2, and AdY3 are adult animals released onto Stirling in Year 1, Year 2, and Year 3 of the translocation

Another point to consider is that we know we do not capture all fishers in our efforts. In fact, because we radio-track animals, we know of at least 6 fishers that were alive and on the study area that we did not capture. Though we capture a relatively high percentage of the animals that are on our study site, we know we do not get them all – adults or juveniles. Thus, it is very likely there are more young fishers out there than we can document. I have included a secondary figure (bottom panel) that shows the percent of animals in each cohort, and by sex, relative to all animals we can document (captured or otherwise).

So there is still uncertainty to the question of how many fishers exist in the northern Sierra. At a minimum we know that 38 fishers were alive at the beginning of our trapping (those captured + those not captured but known through telemetry). This is 2 fewer than the 40 total we released. Preliminary mark-recapture analyses gives a population estimate of 29-45 fishers, and this seems to make sense given our other information. For now, fishers seem to be doing well enough to survive and reproduce. The spring of 2013 is the first year that we will be tracking female fishers, born on Stirling, that will be able to den. Meaning, next fall is the first year we can capture the progeny of fishers born in the northern Sierra Nevada.Documenting this will be another important milestone and indication of how the population might fair in the future.  Hopefully, we’ll see you all next fall for the Fisher Frenzy.


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