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
Well, another fire means yet another post about fire. If you are getting tired of hearing about fire I’m sorry. I can assure you that I’m not all that excited about writing about it, but it is something that takes up a fair amount of our attention.
The Chips fire continues to grow but fortunately (for fishers we know about at least) the fires is mostly moving east. I have included a similar map to the one from my last post showing the change in the fire boundary from last time. For many days now we have choked on the smoke that this fire produces while out trying to collect data on fishers. Working in it is not all that fun, and could pose a health risk, but so far we are dealing with it okay.
The newest fire (smaller but on the related map) started just a few days ago and is known as the Mill fire. It is located in Mill creek on the northern edge of the study site. Currently, the fires is about 1200 acres and about 20% contained. This fire is a bit closer (~1.5 miles) to one of our females that denned this last year (the black crosses on the map). As with the Chips fire it seems to be moving east and away from this female, but as always things can change. Unfortunately, the relative proximity of the fire and the number of fire personnel means we are essentially not tracking this female right now. Though it is interesting and important to know how she responds to the fire we must also take the safety of the crew into account first. Additionally, we would be a nuisance to the fire crews that are fighting the fire and using the same roads that we use. In sum, the fires are affecting our work, thoughtnot shutting us down .
This past winters’ relatively low precipitation levels have made conditions much drier this summer compared to our past two summers. It was clear that fire would be even more of danger this year than in years past. Fortunately (for now), the fires are more nuisance than particularly devastating to the animals we track. With luck, that will remain the case and we will escape any further fires for the rest of the year.
Map of fire locations as of Aug 17, 2012
“Fire! Fire! Ferocious fire!
You restless wall of flame.
Fire! Fire! Roaring higher!
Your fury to never tame.”
– Mark R. Slaughter
Fire is an omnipresent threat to both individuals and populations of fishers. Fires that burn very hot can devastate the over story trees and with them the places where fishers forage, rest, and den. So, we are always aware of the potential effect that a large fire might have on our relatively small population of reintroduced fishers.
In the last week a fire just to the east of our study site (the Chips fire) has been putting up a lot of smoke and growing ever larger. Presently, the fire doesn’t directly threaten any of the fishers we are tracking, but its western boundary is within 5 miles of at least 2 females. Since the fire began on July 29th it has grown to nearly 16,000 acres and is not predicted to be contained for at least another 2 weeks (see the link already provided).
If you examine the included map you can compare the current area of the fire to the area where the majority of our female fishers have been found (blue dots; these data are incomplete and unedited) and where they have denned (black crosses). Though I have not delineated individual females in this figure you can see that a fire of similar area positioned in the middle of the study site would encompass a large number of dens and female home ranges. Additionally, when you consider the fire shown here is relatively small (the largest wildfire can be over 100,000 acres) you can begin to appreciate how easily a single fire event could have dire ramifications for any fisher population in the west (in particular reintroductions).
Hopefully, the Chips fire will have little (preferably no) effect on our reintroduced fishers, but as with most things, we just don’t know what will happen. Fishers are obviously not the only species that are threatened by fires (marten are found in or near this fire), but they are our primary focus in this forum. Eventually, fire will likely have some impact on this incipient population. Those impacts will be related to the population size and spatial distribution of the animals. With luck, the population will grow and expand so that it can withstand perturbations such as wild fires.
Map comparing the area of the Chips Fire to female fisher locations
One of the main things that drew me to fishers was their reputation as a predator. As I mentioned in my last post, fishers are flexible in what they eat and they are extremely skilled at capturing a wide variety of food types. When a fisher kills a squirrel or a woodrat I find it exciting because I know that fisher has helped itself survive for just a little while longer. Yet, fishers are not the only predator out in the woods, and in fact they themselves become the victims of predation (as many of you know).
Research on fishers throughout the western U.S. (including ours) is demonstrating that predators have a significant impact on fishers. In conjunction with our collaborators (IERC and WIL) we can suggest that as much as 60% of our documented mortalities are caused by predation. Interestingly, most of the mortalities we observe occur during the period when animals are actively seeking mates (March – May) or subsequent to the birth of kits when females are actively lactating (April – August).
Distribution of deaths across months for all fishers found dead
It makes sense that animals are susceptible to predation during this period because of the frequency with which they forage as well the energetic demands they may be under. In fact, many studies demonstrate animals foraging in risker ways, or places, under a variety of circumstances (one example).Predators may kill fishers simply to remove potential competition and then simply leave the fisher remains uneaten. Other times they may actually consume the fisher leaving only a few remains.
1F111 found dead
Females and kits are also vulnerable at the den sites as predators such as bobcat (Lynx rufus) often find and climb the den tree. Thus, females are exposed to danger at the den site and while foraging.
Fishers apparently straddle a very fine line between being the hunter and becoming hunted. At present we are still trying to understand the relationships between fisher biology, habitat, and predators that explain the why fishers are more prone do becoming prey for another animal during different times and places.
Bobcat at 20058 den tree
The few remains of females 182F4
I’ve recently been going through some of the pictures that we get from the cameras we place around the dens of females.
20058 sniffs a young tree before going out to forage
We place cameras at these dens to get estimates of how many kits females have, and I think we’ve done a pretty good job doing that (as evidenced by some of the images we have shown in previous posts). One of other benefits though is that we learn (sometimes) about what female fishers are catching to eat and even how often they are foraging.
Two of our females have been particularly informative this year. They live at different elevations, in different vegetation types, and have different litter sizes. One female fisher was captured on camera bringing back a wood rat, a lizard, eggs, and a few other items that we could not identify. The other female returned to her den primarily with squirrels of different varieties. I’ve included a few of those photos in this post. Both these females (released in year 3 of our study) were foraging at all times of the day and very often can be seen leaving the den to go foraging just after brining a food item to their den. Sometimes these two females were returning with prey items 3 times day and these are just the events we capture on cameras. These observations provide support to something we already know about fishers – they are very flexible in the food they eat and they forage often.
20058 returns with a woodrat
20058 returns with egg
2189C returns with squirrel
2189C returning to her den with unknown prey item
Fishers grow quickly in addition to having high metabolic rates. Thus, females must nourish themselves and their young almost constantly. Particularly as the kits get older they need large amounts of energy, and females with large litters are strained even more – a mother’s work is truly never done. The consequence is that females must forage a lot and they expose themselves to risks, like predators (more on this in another post), a higher proportion of their time compared to periods when their energetic needs are not so high. If females can catch large prey items, assuming they are available, then they do not have to forage quite so often and can spend more time at the den with their kits. We still have work to do before we can quantify exactly what all fishers (including females in dens) are eating on Stirling and how this might affect their future success. In the meantime we know that most of our females make it through lactation and that at least some of their kits are also making it. The information we are getting from dens and den cameras is just another important way we better understand how fishers are making a living in the Northern Sierras.