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Thursday, February 28, 2013

Counting placental scars

Muskrat on hind legs
(Seneca Falls, NY)

The course outline said we were going to practice estimating flock sizes as part of our non-invasive techniques unit, but a phone call from NYS DEC Biologist Scott Smith sent my Wildlife Field Techniques course in a whole different direction. Scott is a regular guest speaker each fall in my Wetland Mammals class. I think that is what made him think to call me this past Sunday night asking if I had any students that would be interested in assisting him in counting placental scars on muskrats this week. Instead, I pitched the idea that he bring the 'rats to us and do it as a demonstration with my new Wildlife Field Tech (WFT) class. He agreed and we arranged to receive them on Tuesday and start the thawing process.

Skinned muskrats
(Canandaigua, NY 2/13)
The photos just do not do justice to what 162 skinned muskrats look like. Nor do they even hint at what they SMELL like. They arrived frozen. Each five-gallon bucket seemed heavier than the last. I transferred them to Rubbermaid totes and soaked them overnight to be sure they would be ready for class on Wednesday afternoon. What you see here is the result of careful sorting and thawing: a finished product so to speak. The lids of the aforementioned totes made excellent serving trays. I finished the job with about an hour to spare before class. At this point, students were still expecting a brief lecture followed by time in the field. When class started, I informed them all of the last-minute change of plans. If anyone was disappointed, they hid it well. Of course, at this point none of them had yet to see (or smell) the specimens.

I had prepared a Powerpoint to give the students some context regarding the purpose and methodology of the technique of counting placental scars. As you can see, I chose to title this lecture "Muskrat love". I briefly covered some basic natural history of muskrats including their identification, habitat preference and their sign. Then it was on to vocabulary. Although I do not require my students to always use technical terms, they should be able to recognize them when reading journal articles. Any nursing student would have been at home for the next few minutes as we covered postpartum (the time following birth), parturition (the act of giving birth), uterus ("womb"; where fertilization and fetal development occurs) and placenta (the deciduos organ that supplies nourishment to the fetus). A final term, "placental scar" will take a little more explaining.

Basically, the placental scar is exactly what it sounds like: a scar left on the uterus at the point where the placenta attached. After birth, the placenta is shed and tears away some of the endometrium. As the damage heals, red blood cells pool at the site and a dark spot appears. In some (many?) species, this scar fades. But in muskrats at least, the spots seem to last from year to year. I hesitate to say "last forever", but perhaps that is true.

How would a biologist use these placental scars? Well, each placental scar represents a fetus. Each fetus represents a potential offspring. So biologists count placental scars an indirect measure of fecundity or reproductive effort. In a species like the muskrat, you may be measuring the lifetime effort (since the scars do not fade). In other species (like Arctic foxes) the scars fade and one may be only measuring the size of the most recent litter.

Muskrat tail
By now Scott had arrived and provided some additional insights into the process and how the State will use the data we were about to collect. Scott informed us that all of these muskrats came from a single individual whose trap lines were set in the Montezuma National Wildlife Refuge. I was excited to hear that because MNWR is in my hometown of Seneca Falls. The trapper had skinned each one for the prime fur. We were left with the rest. By now the students were visibly at the point where I could no longer expect them to sit still and listen -- they wanted to "do"! We headed to the shop where I covered a little of the anatomy of the muskrats while Scott made his last preparations.

Front foot of a muskrat
I love the tail of muskrats! They are compressed like the body of an eel and have a really scaly surface. Since I have been into tracking for the past few years, I have been paying more attention to the feet of animals, too. Here is a front foot with the five (yes, five) front toes of a muskrat. Look closely for the stunted inner toe (where your thumb is). I told the students that many tracking field guides provide practical information that may end up being technically incorrect. For example, I have often read that muskrats have four front toes. Well, when you closely examine a detailed track, the fifth toe appears as a dot. And in less than perfect substrate, you wont even see that.... Look closely at the photo of the foot and decide whether you are looking at a right or left front :)

I had one last thing to show the students: the cheek muscles. Just look at the massive masseter muscles! These are the muscles responsible for grinding food, so they are particularly well-formed in plant eaters. Specifically, they are to the right of my thumb and there is a superficial slice present (sorry, didn't even notice that when I was taking the photo).
Masseter muscles of a muskrat
Finally, we begin. Here is Scott ready to show us the proper way to open the muskrat and remove the uterus for inspection on a lightboard. But wait, there is a problem: this one is a male.....

Scott Smith, NYS DEC Biologist

A close up of the male shows the testicles and the musk glands that give this particular species of rat its name:
Male muskrat

The arrow is pointing to a testicle. The other bean shaped item in front of the gonad is the musk gland. We cut one open and managed to detect a slight odor.

The first few females were all young ones with no placental scars as they had yet to breed and produce offspring. Muskrats, like many rodents are heavily r-selected. Their population structure is heavily weighted towards young individuals. The strategy is basically to have many young as most will not survive to adulthood.

Scott set out a scar-less uterus on the light board:
 Here it is close up. The uterine horns show no scars.
Uterine horns of muskrat

"Ah, there we go!", was our first indication that Scott had found our first placental scars of the day. Here is a photo of the uterus removed and on the light board:

Placental scars of a muskrat
 Above, Scott uses his gloved hands to point out the features on the two uterine horns. This uterus is shaped very differently than the ones I remember from tenth grade Health class. The theory is that the two "horns" provide ample space for a large litter. Can you make out the scars on the left side of the photo? There are four distinct dots in the tube-like uterus.

Here is what it looks like when the uterus is in situ:
Placental scars of a muskrat

Wow! Notice above the many scars visible in each horn. We removed it for close inspection:
Placental scars of a muskrat
Again, this probably represents the entire reproductive history of this individual. When the scars remain visible over several years, it is difficult to count them as their will be overlap from litter to litter. You can see some of that in this case.

The students seemed to really enjoy the process:

These animals were harvested for their fur and the carcasses were utilized to help monitor the species and make management decisions for the future. My students were exposed to a new technique and learned other muskrat facts along the way. I didn't want the utilization to end there, so as Scott and the students put the muskrats into the "processed" tote, I went in and removed the heads by hand so we could clean the skulls. I have a thing for skulls, so this was grizzly but pleasant work.
A man that loves his work
But there was one last use for these 'rats. Students helped load all 162 carcasses into my pick up and this morning, with the help of my ATV and trailer, I created a new camera trap set. That's just gotta be better than having them take up landfill space..... stay tuned for that blog post :)

Saturday, February 23, 2013

A Valentine's Day tradition

Deer hearts ready for the camera traps
(Seneca Falls, NY 2/13)
My very first post to this blog (here) described the cardiac lesson my wife teaches each year. Part of the lesson involves dissecting deer hearts. Each year she brings the sliced hearts home for camera trap bait and each year "Cardiac Day" happens to fall near Valentine's Day. This year it matched up perfectly. With 14 deer hearts to set out, I knew my two cameras would be busy...

Setting out the hearts

I only set a few hearts at the first set. The first to find them was a gray fox. Note the two photos are a minute apart:
Gray fox taking bait
(Seneca Falls, NY 2/13)
Gray fox taking bait
(Seneca Falls, NY 2/13)
This set was more open than the second one and the only other visitor of note was this red-tailed hawk. Almost missed him!
Red-tailed Hawk in flight
(Seneca Falls, NY 2/13)
The second set is a bit brushier and I put far more hearts in front of that camera. Gray made an appearance here too:
Gray fox
(Seneca Falls, NY 2/13)
The hawk never made an appearance here because it was too brushy, but the crows found the bait straight away. The hearts are too big for the crows to carry, so they chisel out smaller pieces and I end up with massive amounts of photos:
American Crow at bait
(Seneca Falls, NY 2/13)

I also captured a skunk at the second set, but not the first:
Striped skunk taking bait
(Seneca Falls, NY 2/13)

Striped skunk taking bait
(Seneca Falls, NY 2/13)
The deer hearts are now a part of our February tradition. Best. Valentine's. Gift. Ever.

Now, I just gotta figure out what to get her.....

Wednesday, February 6, 2013

Otter, otter everywhere plus a drop of mink

I have a new class this semester, CON 113: Wildlife Field Techniques. Today we visited a river otter latrine in hopes of collecting some scat (see project described here) and checking a camera for a grad student at SUNY ESF. It snowed last night and this morning, so I was certain that any scat we did find would be fresh.

We arrived at Hi Tor WMA in Naples, NY at 2:45 and hit the trail immediately. It was not to be a pleasant stroll but a march with a mission. Tracking was kept to a minimum so we could maximize our time at the site. Will and Micheal, mentioned in my previous otter post, had checked this site on Sunday and Monday with no fresh scat to be found. They were not entirely sure the site was even still in use. I was anxious to have a look myself and see what evidence the camera had recorded as well.
Main latrine site on January 13th
The pond held what looked like fresh slides and tracks at the main latrine site, the one on the beaver lodge. I say fresh, but everything was coated with snow from the morning. We all agreed that the recent wind would have wiped this slate clean over the weekend. So despite striking out on fresh scat, we felt the site was still in use. And the camera confirmed our suspicion.

Elaina had not checked her Reconyx camera trap since mid-January. I pulled the SD card and we previewed enough of the photos to determine that otters have indeed been using the site regularly. We also found evidence of other visitors. Let's have a look (Nearly all photos are uncropped so you can see the date stamps that help tell the story):

January 14th: Will and his Dad glitter old scat

January 15th: Will is back to check for new scat deposited overnight

Jan 16th: Our first otter photos. Although there are only two individuals in this photo, we have multiple images of three otters together. The Reconyx is set to take photos in a burst of three images. Notice the 1/3 on the top of this pic. That means it is the first of three in this series. The camera than takes another burst of three almost immediately. The result is a lot of images (over 1300 in this set) and what amounts to a poor man's video.

I LOVED that otter standing shot. I have never gotten one personally. There are about a dozen shots of otters standing in this data set. Here is just one more (because standing otters are like potato chips --- you can't have just one)

Jan 17: Red fox. And snow.

Jan 25: Wild turkey. In between, we had many more otter pics.

Jan 26: Mink. Like the otter, mink are in the weasel family and like water. Note the obvious size difference though.

If you are not convinced that the otters are much bigger than the mink, here is a composite image of an otter and mink that should do the trick:

Jan 29: Note the time that this coyote showed up to roll in the stinky otter scat.

Jan 30: It didn't take long for the otter to emerge and investigate the new smell themselves

Although most of the otter photos were at night, some were in the day. Since the night pics are shot with infrared, the only way to see color is in the natural light of daytime. This was my favorite daytime photo

Jan 31: "Neither rain nor sleet nor dark of night shall keep these otters from their appointed rounds"

Feb 2: On Groundhog Day, these two coyotes made an appearance. We can assume they did not see their shadows in the IR flash...

Feb 5: The last otter photo taken before we checked the card at about 4pm on Feb 6th.

Clearly the otters are still using the site. So where are they deposting their scat? They don't HAVE to use the latrines, but why would they just stop? Or did they gradually stop and it only seems sudden? We were able to scrape away some snow to collect old scat for a simple diet analysis the class wanted to do as an outside project. Despite the lack of fresh scat, the trip was a success in my eyes. Field work is never a sure thing...