Follow by Email

Wednesday, July 30, 2014

Small Mammal Trapping: Techniques for safe capture

If I asked most people to quickly name three mammals, I believe most of them would name larger mammals. Pets like dogs or cats, farm animals like horses or cows and zoo animals like elephants and giraffes would probably be common. Yet this is such a skewed sample of the mammals that currently live on this planet. Although our minds go to the more charismatic examples of mammals, the truth is that over 90% of mammal species are small. Merritt (2010) defines a small mammal as one weighing five kilograms or less. For my students and I, that translates to about 11 pounds. Woodchucks weigh about 11 pounds and are among the largest of the small mammals. This blog entry will focus on the smaller small mammals: Mice, small squirrels like chipmunks and shrews.

I am not currently engaged in any small mammal research (beyond simple inventorying of species) but I teach proper capture and handling techniques in my classes. Let's review the equipment first.
Sherman trap at a forest location
Naples, NY (7/14)
The photo at left shows a type of trap called a Sherman trap. Here is the link to the short entry on these traps in Wikipedia. Note that you can go to the company website from there if you want information on sizes, prices, etc. These traps have become the standard for live trapping as they are light, durable and fairly easy to clean. Importantly, they keep the trapped animal secure inside solid walls rather than a wire mesh cage. This provides the captured critter with more protection from weather and they may feel more secure as the closed trap is similar to a hole or burrow that most small mammals would seek for shelter. The flag serves several purposes. First, it makes the trap easier to locate. And by numbering the flags data collection is simplified. This is deployment #13 on the blue transect. Finally, if animals are not processed at the spot they are collected, a flag allows field workers to return the animal to the exact location it was captured.

Traps such as these require bait to increase the capture rate. I mean, a small mammal could stumble in and investigate, but bait is needed to really make this work. Much has been written regarding various bait effectiveness. We use the following recipe ( I believe credit goes to SUNY ESF???):
Sasha makes this for us but I believe this is a SUNY ESF recipe
A few things about this recipe. It is pretty simple and we have had good success with it. Other popular ingredients include raisins, molasses and nuts. It is difficult to break it into perfect squares, so we usually are faced with a plastic bag full of oddly shaped pieces. I tell the students to use bait about the size of a Starburst candy. There is really no need to use more. Traps are checked frequently and there is no chance the animal would need more food.
We also place cotton balls in the traps along with the bait. Cotton serves several purposes. It acts as insulation against the cold of the bare metal and it also gives the captured animal something to do. In my experience, captured rodents often shred the cotton balls and create a "nest".
Other useful equipment for setting traps includes plastic gloves for handling bait, GPS receiver for marking trap locations and a notebook. Please note that there is a different equipment list for checking traps.

To increase capture rate, we typically pre-bait traps for about a week. This entails setting the traps in their transects, adding cotton balls (I like to use two) and bait and leaving the back door open so any animal that enters the trap is free to leave. This can increase capture rate by getting the animals used to visiting the trap for a reward (bait). We try to re-bait every second or third day. It also gives us a chance to see the activity level in the area. If many traps are being cleaned out, we expect a bigger capture when the traps are finally set. One disadvantage of pre-baiting is that larger animals can also find your traps. We have had problems with raccoons, striped skunks and gray squirrels finding and raiding traps. Here are some examples:

Striped skunk raiding a Sherman trap
Canandaigua, NY (11/13)
Last November, we had several transects set on the main campus at FLCC. One was being raided. We set a camera trap and captured this striped skunk opening the trap and eating the bait. Sherman traps open like this to facilitate cleaning (there is a model that folds that does not open). In this case, pre-baiting allowed this skunk to find our traps and raid them numerous times during the week. To counter this, we used a small rope and two tent stakes to hold down each trap and the skunk was unable to get the bait.
Each May we offer a Conservation Field Camp course and small mammal trapping is part of that. Here, two technicians set and bait a Sherman trap specifically targeting flying squirrels.

This time it was a gray squirrel causing us problems:

A final example is more recent. We had traps set at our East Hill Campus in Naples for the past several weeks and one or more raccoons were hitting two of the four transects. Here, Sasha walks away from a trap after setting it. You can see that the back door is closed. The spring-loaded front door is facing away from the camera.

It only took about five and a half hours for this coon to visit. He found this set during the pre-baiting period. In this photo he is starting to reach into the trap.

It is difficult for him to reach the bait without triggering the trap. By now, I bet this guy has enough experience with these traps to know that if he pulls out his arm without the bait, he won't get a second chance as the door will close.

As mad as I get at them, this picture makes me smile. 

The rock wall transect was getting hit as well. Here is a pre-bait photo. Notice first that you are looking at an open back door. The back door is not spring loaded so animals are free to move in and out. To try to increase the camera trap captures at this photo, Sasha placed some natural bait (hickory nuts and mushrooms) on a rock.

Less than two hours later, an eastern chipmunk enters the trap and presumably takes some of the bait.

As hoped, there were lots photos at this location, including some mice in the genus Peromyscus. Check out this mouse in mid-leap with an open Sherman trap in the background. I thought "What a lucky shot! That'll never happen again." Well.....

... I was almost right. Several nights later, I got a photo of presumably the same mouse JUST ABOUT to make the same leap. So I did not get him mid-leap, but I did capture the same behavior a second time.

And then a third... Here I present them to you in the order they were taken. All were captured on different nights. But when I use these in class, I will be putting them in "order" to make it look like a sequence of three photos of one mouse making one jump :)
But back to marauding raccoons. Here is the last image of the trap with the back door open. Notice the edge of the opening. 

Since the last photo, Sasha has closed the back door, set the spring loaded front door, re-baited the trap and turned it around so that the opening is still in the same direction as it was during the pre-bait week. Can you see how the edge of the opening looks different than in the photo above? The front door opening has a bit of a lip that the door closes against.

Here is the very next photo captured. The door is closed and the mushrooms have been moved. Obviously, the camera missed some things.

Not far behind was this raccoon. When we checked the traps, this one was tossed open and empty. Was there a critter in the trap when the coon opened it? Probably, but we will never know for sure.

Once we capture a small mammal, the handling protocols we use are designed to assure a safe and quick experience. For example, shrews are particularly susceptible to trap-stress, so our protocol calls for processing them first. Students are instructed to keep noise to a minimum. We still talk, but we use our inside voices. Students work in pairs with one wielding the clipboard while the other processes the animal. And as mentioned previously, animals are returned to the exact location of their capture.
Let's start at the beginning. Students check all the traps in a given transect. If there is a small mammal captured in a trap, the trap label is marked with the flag number and color and taken to the processing location. Since the goal of the activity is to teach the students how to participate in all aspects of small mammal trapping and handling, we process the animals in a central location so we can all learn from all captures. You may wish to process animals right at the capture site depending on your research question.

Removing an animal from the trap is not difficult, but does take some practice.
Here, FLCC professor Clinton Krager places a large Ziploc bag over the back door of a Sherman trap. The bag opening is folded over so the animal cannot escape. We use plastic bags for two reasons. It is easier to see the animal in the plastic bag rather than a cloth bag and therefore makes the process go faster. The animals do not spend much time in the plastic bag so they do not run out of air or get too hot.

Sometimes an animal is reluctant to leave a trap even after shaking it a little. A nice trick is to aim the opening up. Often an animal will scoot right out.
Author removing a flying squirrel from a live trap
Photo credit: Alyssa Johnson
When the animal is in the bag, the bag and contents are weighed. Usually, the cotton and some bait are in the bag as well as the animal. Once the animal is removed from the bag, the bag and contents are weighed and subtracted from the total to find the true weight of the animal.

Weighing a mouse with a spring scale
Canandaigua, NY (4/14)

The next step is removing the animal from the bag. Here, Clinton holds the bag against his leg and uses one
hand outside of the bag to hold the animal while sliding his other hand onto the bag to grab the animal by the scruff of the neck. Again, the animal spends a short amount of time in the bag and the researcher can see the animal easily. I have also found that animals will latch on to cloth bags with teeth and claws making them harder to extract. This technique works very well with small small mammals. It does not work well with larger small mammals like gray squirrels. Oh, and flying squirrels have lots of loose skin and can be difficult to hold so that they cannot reach around and bite.

Sasha is holding an eastern chipmunk properly. This was her first chipmunk. They can be bitey, so she was using gloves. The data we collect is pretty basic. I mentioned weight. We record the species, gender, total and tail lengths and age (adult, immature or unknown).

If we are holding an animal for any length of time (to let students observe it), we place it in a jar. The jar
makes it easier to see and most animals calm right down when placed inside. Meadow voles will begin grooming almost immediately when put in a jar.
Finally, we have experimented with different methods of marking small mammals. Ear tags are available in various sizes and easily attached to most critters (not shrews). Since I am not engaged in a research project that requires permanent marking, I do not ear tag. However, we do use non-toxic markers to make an X on the belly. It does not last very long, but it works for a quick mark-recapture study.

Male with enlarged testes and large distance from the
anus to the genital
Naples, NY (7/14)

Monday, April 28, 2014

Northern Short-tailed Shrew Nest, Latrine and Cache

Greetings everyone! I have been slow to blog in 2014 due to a very busy schedule. This weekend's wildlife encounter forced me out of exile and back into the blogosphere. On Friday evening, we hosted the FLCC Student Chapter of The Wildlife Society for a nice spaghetti dinner (thank you Laura!) followed by a woodcock walk on our property. We checked for tracks in muddy spots, looked at muskrat lodges in the wetland, learned a little about native warm-season grasses and tried to find spring peepers in the pond. But one of my highlights is always flipping over some old pieces of siding to see who might be living underneath.
Short-tailed Shrew
Seneca Falls, NY (4/14)
I should explain that I have been a "flipper-over" for a very long time. I saw my very first weasel when I was a teenager by looking under an old sheet of plywood. I found my first Norway rat under an old automobile hood. Childhood successes such as those made me a life-long investigator of all things flip-able. So I was very excited when our first piece of corrugated siding produced a short-tailed shrew. One of my students caught the shrew and I held it for all to see. Sasha (club adviser and FLCC Technician) noticed a nest and we concluded it was the shrew's. It was empty.
On Sunday, my wife and I took a walk to look for antlers and decided we could risk disturbing momma shrew and flipped the siding again. We waited patiently and within a few minutes, the shrew began to nose around at her newly disturbed world.
Molting short-tailed shrew
Seneca Falls, NY (4/14)
In the photo above, you can see a bit more of the shrew and she is clearly molting out of her winter coat. I guess it makes sense, but I honestly never thought of shrews molting before. Notice how small the eye is. Shrews are not known for having good eyesight. She slowly emerged from her tunnel and made her way into the grass...
Northern short-tailed shrew emerging from tunnel
Seneca Falls, NY (4/14)
There is the short tail that gives this species of shrew its common name.
Seneca Falls, NY (4/14)
I decided it was worth it to peek into the nest. I have only ever found one other shrew nest and blogged about it here. But if there were shrews in this nest, they would be less than two days old. We carefully peeled back the dried grasses to find a ball of leaves. And inside the leaves were eight tiny altricial shrews.
Baby shrews in nest
Seneca Falls, NY (4/14)
Look for five digits on the front foot to rule out mice
Seneca Falls, NY (4/14)
Baby short-tailed shrews in nest
Seneca Falls, NY (4/14)
We carefully covered the babies and I quickly snapped a few photos of the other items under the siding. There was a large pile of scat within a foot of the nest. I cannot imagine it was made by any other species (especially given how fresh some of the scat was). However, the diameter seemed rather large when I compare it to published information. Elbroch says up to 3/16 inches in diameter and although I did not measure the scat, it sure seemed larger than that. He also states that when they are feeding on worms or other soft bodied animals, the scats would be "soft squirts". Well, that certainly describes the freshest of the scats. Here is the latrine:
Short-tailed shrew latrine
Seneca Falls, NY (4/14)
Short-tailed shrew latrine. This is the end that was closest to the nest.
Seneca Falls, NY (4/14)
The piece of corrugated siding was about four feet by three feet. Besides the nest and the latrine, I noticed two spots with concentrations of earthworms. Now, this entire area was bare of vegetation, yet the only earthworms to be seen were in two small areas. They were alive but slow moving. I have to believe they were cached by the shrew. Have a look:
Worms cached by short-tailed shrew
Seneca Falls, NY (4/14)
I wonder if the worms had been injected with some of the venom these shrews have in their saliva. That would explain how they could be cached alive. The large one near the top of the photo looks damaged.
I hope I did not disturb her too much but I learned a lot from this encounter. Latrine, cache, nest.... it was all here! I will check again after the young have left the nest and see what else I can find.

Monday, March 10, 2014

Christmas on the Baja Peninsula

I have been away from blogging recently due to a busy schedule and have honestly missed it. It has been
Family portrait on the island of Espiritu Santos, Baja Mexico
good therapy for me to write and I have learned a lot in the process. It is March as I write this but my thoughts have returned to our last family adventure: a Christmas trip to Mexico. We booked our tour through ROW Adventures and enjoyed every bit of it. We hiked, kayaked and snorkeled. We swam with sea lions and whale sharks. It was a true adventure! Five days and four nights of kayaking and camping were complimented with a few nights in a hotel and two nights at a lodge. Here are some of the highlights.

Christmas was on a Wednesday this year. That meant the public school vacation would extend 16 days. We decided to take advantage of that block of time and found a tour that advertised great activities and some interesting wildlife encounters. We left the unusually harsh NY winter on Christmas Eve and flew through Mexico City then connected on to La Paz, Mexico on the Baja Peninsula. That evening, we met our guides "Charo" and Damian, as well as the other family that was on the kayaking portion of the tour. We were fitted with wetsuits and snorkeling gear and given dry bags to pack our gear. We left early Christmas morning by motor boat for the island of Espiritu Santos and four nights of camping.
Laura and Danika, Christmas Day 2013
When we arrived on the island, we were given some additional instructions regarding kayak operation and how to pack it evenly. Each day we paddled only about four hours, giving us enough time to set up camp at each beach and explore the upland areas a bit. We saw rays jumping, dolphins swimming and everywhere there were birds. Gulls, pelicans and frigatebirds were the norm.
Magnificent Frigatebird, male
Baja, Mexico (12/13)

Picture the habitat of southern Arizona, but along the ocean. Once I turned from the ocean, I would swear I was in the Sonoran desert south of Tucson. The cardon cactus looked to me the same as the saguaro I had seen years ago in AZ. However, the fact that we were on an island with very little fresh water in the Sea of Cortez meant a very muted fauna. So although the bird life was abundant, we only saw one species of land mammal (Black-tailed Jackrabbit).

The morning of our final day on the island was spent taking a short motorboat trip to snorkel with sea lions at a small rock jutting up from the ocean. This was one of the highlights of the trip for me. The sea lions ranged from tolerant to outright social with us. If you watch the video here you will see that one of the sea lions even grabbed on to my arm for a moment or two. Warning: That video is about 11 minutes long. I just couldn't bring myself to edit it down any shorter. I won't be offended if you just watch a little :)
Still photo from GoPro camera
Baja, Mexico (12/13)
Whale shark photo with GoPro
After snorkeling, we headed back to camp to pack. Low tides forced us to shuttle our gear through shallow water to the motor boat that came to pick us up. We arrived back in La Paz with plenty of time to unpack, shower and get ready for our group dinner together. The next day, we were driven to the harbor and met Dr. Deni Remeriz for a morning of searching for whale sharks. We had never even seen a whale shark no less swam with one, so the entire Van Niel family was excited for this adventure. Deni was very free with her knowledge of all things whale shark and you can find out more about her and her organization here. For a video of our adventure on YouTube, click here.

Our final two days were spent in Todos Santos, a small town with plenty to offer. We went horseback riding on the beach, took a cooking class, hiked and even got to help release sea turtles. One of our guides (pictured here) was Citlali. Turns our that means "morning star" in Aztec. In turn, we taught her the name of our daughter "Danika" which is morning star in Danish :). Here is a photo from the cliff hike. We had numerous sightings of humpback whales while on this hike.

On our last evening, just before dinner, our guide and driver told us they had a surprise for us. They had talked to the man that coordinates a sea turtle rescue operation and he was confident that there would be freshly hatched sea turtles to release to the ocean. This story deserves an entire entry by itself. But the short version goes like this: The olive ridley sea turtles come to the beach in Todos Santos and lay their eggs. But vehicles are allowed on the beach and would crush the eggs if they were left in place, so volunteers dig them up and re-bury them in an enclosure on the beach. When they hatch, they are collected and brought to the ocean where they must fend for themselves. It takes about 10-15 years for them to reach sexual maturity. There were about a dozen of us there to witness the release and the gentleman in charge picked Danika to carry the turtles to the surf.

All told, this was one of our most memorable trips.
Sunset in Mexico