Posts Tagged With: trapping

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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Spot Trapping

At the end of our Fisher Frenzy last fall, most of us were pretty satisfied with the fruits of our labor. We had captured more fishers than in any of the previous years’ efforts, affixed all of our available VHF collars on females, caught a good crop of juveniles, and all of the fishers we examined seemed to be in pretty good health. What else could we ask for?

Well, there was one question that I couldn’t get out of my head – Where are all of the adult males? We only captured three, and knew of a 4th that was on the air but never captured. This is in contrast to 17 adult females caught during the same time period. Of course, we expect to find fewer males due to their larger home ranges, but only capturing three adults? Something seemed wrong here.

After we finished up our main Fisher Frenzy, the team here continued to run a small number of traps, attempting to target particular fishers that avoided capture. For most of December and January, we didn’t have much success. We kept recapturing fishers that we had caught during the Fisher Frenzy, but the target fishers wouldn’t enter our traps.

However, to our delight a couple of weeks ago, we caught a fisher that we had never seen before. It ended up being a large 4.8 kg male!  He was in excellent condition, and we put a collar on him. He was in an area that we aren’t currently tracking any other adult males (but we did have plenty of traps in this area during the Fisher Frenzy).

Starting to wake up.

Starting to wake up.

Dustin and Pierce monitoring the first male captured.

Dustin and Pierce monitoring the first male captured.

Fast forward three days later. In the exact same trap, another unmarked fisher was captured. Once again, it was an adult male! This guy was slightly smaller than the first (4.3kg), but was also in really good condition. We put a collar on him as well, and let him go.

Capturing these males was important for a variety of reasons. First off, it will allow us to gather some location data on them so we can see what areas they occupy. Secondly, it reinforces to me that there are fishers out there that can go undetected for years, and that we aren’t catching all the animals that are out on the landscape. We won’t know the exact age of these males for a while, but based on their size and developed sagittal crests, both of these guys were probably older than two. This means they avoided capture during the Fisher Frenzy 2013 and 2014, and possibly even 2012. Of course, is could be simply that they spend most of their time outside of the main Stirling tract, and were just now passing through the area for some reason (perhaps scoping things out as we get nearer to breeding season). We don’t have the resources to trap many of the areas adjacent to Stirling, so any fishers occupying those lands might go undetected. Hopefully their collars will give us many good locations over the next year.

Personally, it eased my fears of something more serious going on with the males. It’s hard not to go through all the doomsday scenarios after not catching very many. Possibly they simply aren’t as prone to entering traps as females, or maybe many males are partially occupying areas we don’t end up trapping. Whatever the reason, it was a welcome relief to capture these two guys.

Sean babysitting as he was starting to wake up.

Sean babysitting male #2 as he was starting to wake up.

Andria, Roger, and myself waiting for the drug to take effect.

Andria, Roger, and myself waiting for the drug to take effect.


First male captured.

Getting a weight.

Getting a weight.

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Fisher Frenzy 2014

We recently wrapped up our month-long fall trapping event (aka Fisher Frenzy).  This is the 4th year we have conducted this large scale trapping event, and 2014 proved to be our most successful to date.  Over the course of the month, we were able to capture 32 individual fishers!

We conduct this trapping effort for a variety of reasons.  First and foremost, it allows us to affix radio-collars on fishers.  Most of our collar’s batteries tend to last a little over a year, and thus the collars we put out in 2013 do not have very much life left.  The new collars we put out should last us until next year at this time and allow us to track the fishers throughout the year.  We also learn a lot by examining the fishers we do catch.  We can get an idea of overall condition, age, past reproduction, parasite load, and old or new wounds.  Sometimes, we even get the shock of seeing something completely unexpected, like imbedded porcupine quills!

On a more personal note, trapping is the time of year that we actually get to see fishers (as well as some of the other forest mesocarnivores) up close and personal. This is immensely enjoyable to me, as most of the year it’s rare even to get a glimpse of the fishers we are tracking on a daily basis.

As in previous years, we spent the first two weeks trapping the east side of the district before moving to the west side for another two weeks.  On the east side, we totaled 36 fisher captures of 24 individuals (18Female:6Male).  11 of these were fishers that we had never captured before (6F:5M).  Our success slowed down on the west side of the district, but we did manage 17 total fisher captures of 8 individuals (5F:3M).  Of these, 4 were fishers who had not been caught before (3F:1M).

In total, we ran over 2,700 trap nights!  We recaptured 17 fishers from previous years (14F, 3M), as well as picked up 15 fishers (9F:6M) that we had never caught before.  Our overall trapping success rate for fishers was 1.9%.  Besides fishers, we also capture quite a number of other animals in our traps.  We managed to catch 45 spotted skunks, 32 ringtails, 15 grey foxes, 3 striped skunks, 2 raccoons, and even 1 bear cub (luckily mom didn’t seem to be around).

Every year, there are a few wise fishers that manage to evade our traps.  At the end of trapping, we had 4 known on-air fishers that we did not catch.  Adding those animals to the number of fishers we did catch gives us a “minimum known alive” population size of 36 individuals.  Of course, it’s likely we are not capturing all the fishers that are out on the landscape (we are also not able to trap every area we would like to because it’s not logistically feasible).

In order to run trapping at such a large scale (~100 traps open per night), we require a large amount of personnel, time, and effort.  This year, we had over 25 people come out to help us with our daily trap checks and examinations! All of the project cooperators (California Fish and Wildlife, North Carolina State University, Sierra Pacific Industries, US Fish and Wildlife Service, and Wildlife Conservation Society), made large contributions to help pull this event off.  A HUGE thank you to everyone who gave their time and effort to help make this year’s trapping a success!

Here are a few pictures from this year:

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A Single Hair

It might not look like much. In fact, you might not notice it at all. But a single hair is all Jesse Hogg needs to help tell an important story. Jesse is working with the U.S. Fish and Wildlife Service and other project collaborators as a Klamath Basin Tribal Intern. Jesse began his work with us on the Eastern Klamath Study Area (EKSA) which straddles the California/Oregon border. The EKSA is one of several locations where project biologists captured and relocated fishers to the Stirling District of Sierra Pacific Industries. We are using non-invasive methods to monitor the fisher population of the EKSA to evaluate if the removal of the fishers we relocated was detrimental to the population. Jesse set, checked, and collected hair samples he found in devices designed to snag hair from local fishers. The genetic material stored in the root of hair can reveal an animal’s species and sex and characteristics used to identify unique individuals. After wrapping up a successful season, Jesse is now working in Stirling to help monitor radio-marked fishers.

The Klamath Basin Tribal Internship Program seeks to inspire young native community members to develop the technical skills required to monitor and manage species and habitats, to pursue college-level educational opportunities, and to succeed in conservation-focused careers. The program provides employment and professional development opportunities for members of six native communities of the Klamath Basin of northwestern California and southwestern Oregon.

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Tracks, Hairs, and Bears, Oh My!

Tracking fishers using VHF telemetry is an extremely useful method for obtaining lots of different information about the animals, it’s also pretty fun! However, in order to implement this method, fishers must be trapped, handled, and fitted with a collar. As biologists, we love having the opportunity to work so closely with a species, but we also love the idea of gathering quality data without ever having to touch an animal. We call this type of data collection “non-invasive”, and it is the eventual goal of this project to use only non-invasive methods to monitor the fishers here on Stirling. In order to reach that goal, we recently ran a pilot study to test how well non-invasive techniques would work in collecting the information we need.

In mid-September, I ran this six week pilot study using track plate boxes fitted with hair snares (see “Field Methods” tab), as well as remote cameras. I placed 45 boxes and 15 cameras in the woods, spread throughout the western half of our district. I checked each box once every 6 to 8 days, collecting tracks, hair and photos that were left behind during that time. The baited boxes attracted lots of different visitors! Bears were especially fond of them; I commonly found the boxes ripped open and dragged away from where I placed them. Gray fox, squirrel, wood rat, ringtail, spotted skunk and even mountain lion are some of the other species I detected.

The most important visitors were the fishers, of course. Adult and juvenile animals, both male and female, investigated my boxes regularly. It appears the non-invasive methods will be a very useful tool for monitoring the fisher population here, and we plan on continuing the pilot study later this year. We are very excited to see what the data will tell us!

Below is a slideshow of images I captured using remote cameras during the study.

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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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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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Fisher Frenzy

Fall brings about a good time to try and trap fishers, and we have been very busy over the past month doing just that.  This intensive trapping effort of the Stirling district, dubbed “Fisher Frenzy”, finally concluded this past week.  The trapping that we conduct here serves many purposes (some of which will be discussed in future posts).  Importantly, it allows us to examine the condition of both juveniles and adults, and affix radio-collars on selected fishers so we can track them in the future.  This year, we split the trapping effort between two different sides of the study area, running the first 14 nights of trapping on the eastern portion of the study area, and the last 14 nights on the western side.  When we talk about different sides of the study area, we are using the north-south running Butte Creek as the divider.  This split has more to do with logistics than actual geography.  The sides are accessed from different highways (and getting across the creek is time consuming).

The beginning of this years’ event coincided with the first major storm of the fall, which soaked the lower elevations and left 1-2 feet of snow up in the higher areas of the study area.  This made for a challenging couple of days, and closed many of the traps temporarily.  Luckily, a dry spell followed which allowed us to get nearly everything re-opened, and over the two week period we were successful in capturing quite a number of animals.

On the east side, 16 individual fishers were trapped.  We captured a good mix of both adults and juveniles, males and females.  Total number of fisher captures on this side was 26, with a few animals being trapped more than once.  In addition to the fishers, we caught a variety of other mesocarnivores in the traps.

After the first two weeks we left our comfortable accommodations (the former SPI office in Stirling City) to camp out on western side of the study area.  Again we got a fair amount of rain and a bit of snow, but caught a good number of fishers on this side as well.  Over the final 14 days, we were able to capture 13 individual fishers (17 total).

In addition to only looking at fishers, this year some of the folks from the CDFG Wildlife Investigation Lab and the Integral Ecology Research Center came out to do examinations of some of the other animals that we catch.  Spotted skunks, ringtails, and grey foxes were processed, with the general purpose to look at disease exposure in fishers and these other forest mesocarnivores.

Overall, we are pretty pleased with the way things went.  Between both sides, we caught a total of 29 individual fishers during 28 days.  We know that we failed to capture a few animals (those with collars which are still working), but that is expected.  Some of the animals are in areas that were hard to get to (especially after the first snow), and some seem to just be very trap shy.  Now we have the task of keeping track of all these new animals, and it will be interesting to find out where some of these younger animals will end up living.

Over the entire month, we ran somewhere in the neighborhood of 2500 trap nights.  This was a massive effort that could not have been done without the help of many people.  Specifically, we got some much needed labor from Sierra Pacific Industries, as well as the use of the old Stirling City office so we didn’t have to completely rough it for a month.  US Fish and Wildlife provided many helping hands, as well as a life-saving wall tent and stove in the latter parts of trapping.  Among many other things, Fish and Game provided the mobile lab which made processing fishers less stressful than working them up out in the field. A huge thank you to everyone who came out to lend a hand!

Here are some pictures of the event.  Enjoy!

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Curiosity killed the cat (sometimes)

Now that we can see the other side of summer we begin preparing for the fall. Last fall we had an extensive trapping session on Stirling where we recaptured a number of our reintroduced fishers as well as several kits. To effectively use our traps we need to have as much information as we can get about where fishers are or where they might be. A big part of getting that information is using our cameras to detect fishers in areas that we might not trap otherwise.

In the last few weeks we have begun deploying our cameras to different parts of Stirling. We will sample an areas for about 4 weeks and them move on to a new area. Cameras are checked once a week and the station is re-baited with chicken (held in a bait sock) and gusto. While going through some of these photos I noticed a black  bear visiting one of the stations. No surprise there since bears come to bait stations quite often, and in fact we find them something of  a burden when they destroy cameras. In this sequence, however, I noticed something else. A black shadow off in the background of the picture -with eyes. Closer inspection shows it to be just an ordinary black cat, but what it was doing at a bait station while a bear was there is a real mystery. It almost appears that the cat is just watching the bear almost contemplating pouncing upon it? Eventually, the bear notices the cat and it kind of wanders away, but never very far.

In this case curiosity didn’t kill the cat (that we can tell), but it demonstrates the interesting, and sometimes weird, things that go on out in the woods. No, its not the find of the century, but its puzzling and a for me kind of amusing. I’d be interested to know what the cat was thinking. Maybe the whole incident was just coincidence.

A cat (red circle in background) watches a bear at a baited camera station


Bear sees a cat a bait station

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The Depths of Despair

Fisher in Box (photo: Tati Gettleman)

Today Rob and I went and checked some traps that Kevin set and opened several days ago. Sadly, we caught nothing! We have adopted a philosophy on the project relating to failure and trapping. Essentially it states that if you display any optimism that you will capture a fisher then you are certainly doomed to failure – you’ll capture nothing. If this goes on for much time at all then you inevitably develop a deep malaise that  can easily transition into despair. About the time that you feel your endeavors are completely pointless and futile is generally about the time that you begin catching fishers.

Male fisher about to enter Trap

This is a peculiar phenomenon that has been observed independently by multiple biologists. Scott Yaeger (our good friend and collaborator from the US Fish and Wildlife Service) initially made me aware of this concept several years back when he noted that he was having good success capturing foxes, but that once he believed he would catch foxes he was unable to ever catch another. Another day while Richard Callas (again friend and collaborator from Cal Fish and Game) and I were trying to catch fisher for the 1st year of the translocation effort, without success, he commented that he has also made similar observations relating the optimism of the researcher to the likelihood of success. In fact, it was during his description that he initially mentioned that we would need to sink into the “Depths of Despair” before we might have any success. Moreover, as Richard noted, the despair must be genuine. If you invoke the depths of despair with secret belief that it will bring success then you will always be disappointed. This is why you always capture animals on the last trap of a long line that produced no other animals, or on the very first trap that you feel was placed in poor habitat and could never catch an animal.

Shelly with sedated male fisher

No work as been done on how many, or if all, the biologists contributing to a project must be in the depths. Perhaps it is neccessary for only 1 truly caring individual to fall into this strange abyss of perceived failure? Maybe more importantly no one has established a statistical link between disposition and captures success, and it stands to reason that no one ever shall. In any case, tonight we sit. Perhaps not quite to the point of despair, but certainly with little hope that our traps, which did so poorly the last few days, will redeem themselves or us.  I include some photos from a happier time when traps were full of fishers and our moods more salubrious.

Fisher in Trap

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