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Weighed down by my camera gear and clearly not as fit as the pika crew farther up the trail, I stopped to catch my breath and wonder why I had agreed to go in search of plague in Lassen Volcanic National Park.

That's right, plague. The word normally conjures images of the Black Death of the mid-1300s, or maybe rats on a ship. You don't normally think of small, cute, furry mammals that can contract and spread the deadly disease in a national park. It would never have occurred to me that plague could be found within the confines of this national park in Northern California, but it is here.

That's why on a mid-October morning I had agreed to join Jonathan Bowser, a biological technician working as a contractor for the U.S. Geological Survey and the National Park Service, and his “pika crew” to learn about their research and field methods to study plague’s existence and effect in the park, with particular attention to its effect on pika.

Yersinia pestis, the bacterium responsible for plague, is a “vector-borne disease” carried by fleas. While rare in humans, the National Park Service reports plague is “naturally occurring” among small mammals at both high and low elevations within Lassen. Plague’s deadly cascading effect impacts not only small mammal populations, but also the larger carnivores that eat the small mammals.

“There is lots of variation between species and individuals of species,” according to Bowser, so plague doesn’t have quite as much effect in foxes, wolves, or bears. Regarding people, Bowser said that “generally, humans are safe from plague even if they spend a lot of time outdoors. Keeping a respectful distance from wildlife is best for the sake of the animals as well as the human’s health, [and] it is just good practice. The most common ways plague spreads are from flea bites or handling dead carcasses. It [plague] cannot be spread from an animal bite … cases of plague in humans in the U.S. … are very rare [and] if caught early is easily treated with antibiotics…”

In other words, don’t let plague keep you from enjoying Lassen or any park unit. Just keep a safe distance from the wildlife, including those cute little critters looking for a tasty handout.

Regarding plague in the park, why study pika in particular? According to the NPS, American pika are a “charismatic indicator species” whose population numbers reflect various environmental conditions. In addition to being “interested in how active plague is in Lassen Park on a landscape level and what animals are affected by it, pika is one species of interest because their numbers have been declining and part of it is due to climate change, but there is something else causing pika numbers to decline, and we suspect it could be plague,” states Bowser.

Unloading the study gear, Lassen Volcanic National Park / Rebecca Latson

Hitting the trail for a morning of field research, Lassen Volcanic National Park / Rebecca Latson

My morning in the field with the pika crew of Bowser, Hannah, Joe, Kat, and Megan began early – 6 a.m. In a couple of vehicles, we headed out toward the Bumpass Hell trailhead area. I remember standing on the trail at one point with my camera aimed in their direction, panting from the effort of trying to keep up with the crew as they hiked to their trap transects carrying not only their backpacks but also equipment for processing any small mammal they might catch in their live traps. 

A Sherman trap setup, Lassen Volcanic National Park / Rebecca Latson

Early mornings are for stuffing those traps with treats smaller mammals like pika (and chipmunks, squirrels, and deer mice) might find tempting: sweet oats, peanuts, apple bits, and molasses. For empirical purposes, I even smelled the container of goodies and got a whiff of stale peanuts (I’m pretty sure the wildlife is not as discerning as we humans regarding freshness).

Along with cotton padding, handfuls of those goodies are thrown into either one of two trap types: Sherman (the smaller solid metal traps) or Tomahawk (the wire mesh traps that look more like cages). These traps are set in spots a small creature might frequent, sometimes camouflaged with talus rocks, and marked with little yellow flags. The traps are left open and enticing to whatever might come along (including much larger animals that can’t fit into those traps but do leave tooth mark and saliva calling cards).

During their July – October research season at Lassen, the pika crew set 6,000 traps in more than 15 different areas, both at high and low elevations.

Traps in the talus: a Tomahawk cage on the left, and a Sherman trap on the right, Lassen Volcanic National Park / Rebecca Latson

Once the traps are filled with food, it’s time to wait a couple of hours, give or take, before the traps are checked. This wait time was a good opportunity for me to talk to everybody, not to mention enjoy the stunning park scenery bathed in golden light by the morning sun.

Lassen landscape, Lassen Volcanic National Park / Rebecca Latson

Bowser told me the idea of studying pikas for plague started a couple of years ago with a pilot study. The Dixie Fire (2021) shut down the second season, making this year the first full season of field work. There’s funding for two more seasons, which is a good thing, since as much data as possible will enable park staff and scientists to understand “the dynamics of plague [in Lassen] and eventually contribute to a plague management plan for the National Park Service that will help manage outbreak of plague and species conservation related to plague.”

Although possessing varying backgrounds, Hannah, Joe, Kat, and Megan are united in their love of working outdoors and their strong interest in the plague aspect of the research they help Bowser conduct. They told me about themselves, and I told them about my work with the Traveler. Kat, a botany technologist also helping with another research project out in the park, took time to patiently answer my plant-related questions (for a future National Parks Quiz and Trivia piece, folks).

Upon completion of the wait time, traps were checked. While no pikas were captured on this day, several chipmunks and a golden-mantled ground squirrel awaited the processing station set away from the trail and out of sight of hikers. Why out of sight? Well, hikers are curious and would want to know what’s going on. The morning tasks the crew performs are time-sensitive, and while they will answer hikers' questions, it’s important they conduct their field efforts within a specific timeframe. That, plus they don’t want anybody coming along to grab-and-go with research equipment like the extra traps, extra marker flags, or even the table on which processing occurs.

Setting up the processing station, Lassen Volcanic National Park / Rebecca Latson

Again, all this processing is done within the space of a minute. The crew works quickly, efficiently, and carefully so as not to injure the animal. In the accompanying images, you’ll notice they hold the chipmunk gently but firmly, with fingers around the back of the neck (rather than the front, which would cut off air flow) while the rest of the hand supports the animal’s bottom end.

The animals were processed then released, data collected, and prior to noon, we all headed down the trail back to the parked vehicles. As Bowser drove us back to the Lassen's park headquarters, he stressed the importance of a good crew and how pleased he is with his own crew. These interns, paid a nominal daily stipend, give up a portion of their normal lives to live and work under sometimes less-than-optimal conditions. From my own observations, I could see how easily they got along with each other and how dedicated they were to the fieldwork. I know it takes a cohesive group of people to successfully conduct any sort of research, and I think this pika crew fits the bill.

With only a few days to spend in any park, I must usually pick and choose from my bucket list of things I want to do  and places I want to go. Once I accomplish those goals, anything after that is a bonus. For me, that morning out in the field with the pika crew was the cherry on top of a great stay at Lassen, providing insight into some of the fascinating ongoing research within that national park.

The Pika Crew: Megan, Hannah, Joe, Jonathan, Kat, Lassen Volcanic National Park / Rebecca Latson

The Pika Crew: Megan, Hannah, Joe, Jonathan, Kat, Lassen Volcanic National Park / Rebecca Latson

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Where might one find the analysis of the fleas?


A. Johnson, While I do not know for certain, it seems logical that flea analyses would be sent to Jonathan Bowser, since he is conducting the research.


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Testing For Plague

Collaring a tiny cousin of your typical rabbit for biological samples is easier than you might imagine.

A major portion of this plague study necessitates gathering data from the animals trapped and requires several steps that are rather quickly done.

Step 1: weighing the chipmunk, Lassen Volcanic National Park / Rebecca Latson

Step 1: weighing the chipmunk, Lassen Volcanic National Park / Rebecca Latson

The animal – in the case of the accompanying photos, a chipmunk – is removed from the cage and placed into either a zip loc bag or what looks to me like a pillowcase to be weighed in grams. Several scales with differing weight allowances (all in grams) are available depending upon the size of the animal.

Once the animal is weighed, it is emptied head-first into the container used for anesthesia. While I did not ask, it seems to me the head-first approach keeps the animal from biting the technician and/or easily escaping the anesthesia chamber (which, in this case, looked similar to an empty Costco jar of mixed nuts).

The anesthetizing agent is attached to the jar lid, and holes are placed at the bottom of the container for air flow. The anesthesia doesn’t completely knock out the animal but is enough to keep it still and compliant for one minute of processing before it reawakens.

Sometimes, the animal may need to be placed back in the anesthesia chamber if they wake up prior to process completion. Anesthesia not only means less stress on the animal, but also knocks out the fleas, making them easier to collect.

Step 2: anesthetizing the chipmunk, Lassen Volcanic National Park / Rebecca Latson

The the sex of the anesthetized animal is determined, its ears tagged, and it’s then microchipped (PIT tagged – Passive Integrated Transponder like the chips you may have placed in your pet dog or cat). Once the microchip is inserted, a hand-held scanner reads the chip data.

The 12-digit number on the chip identifies individual animals. All other data is written down on paper, then entered into a database back in the office. They don’t PIT chip deer mice because they are just so tiny, and the crew brings face masks to wear when processing mice because of the possible presence of hantavirus.

An itty bitty ear tag, Lassen Volcanic National Park / Rebecca Latson

Step 3: tagging the chipmunk's ear, Lassen Volcanic National Park / Rebecca Latson

A vaccine or placebo is injected into the animal. According to Bowser, “the vaccine is similar to vaccines in humans. It only protects from future infections. If the animal already has plague, then the vaccine will not be very effective, but could offer some protection.”

The idea with the vaccine is that if enough animals are protected, then “it slows the outbreak of plague over a small area. The vaccine will protect for a while, but we do not know if it is lifetime protection,” he said.

Step 4: injecting the vaccine or placebo, Lassen Volcanic National Park / Rebecca Latson

The animal is combed for fleas (which can measure 1 – 3 mm long). If fleas are found, they are picked up with tweezers, deposited in a small tube, and sent off for analysis, which might take up to two months for results.

Bowser and his team “are still trying to understand the dynamics of plague and what conditions cause it to go from low mortality rate to high mortality rate. Fleas could come back positive for plague, but that doesn’t mean the disease is very active. The best way to determine how active plague is in an area is by comparing survival rates of vaccinated with unvaccinated like in this study.”

Step 5: combing for fleas, Lassen Volcanic National Park / Rebecca Latson

The animal is measured: total body length, tail length, foot length, and ear length. Why all these measurements instead of just a single body length? One reason is for identification purposes.

To me, the chipmunks they processed all looked alike, but they really do differ in their dimensions. Another reason for those measurements is to create a health index for the animals similar to BMI – Body Mass Index – in humans.

Step 6: measuring the body length, Lassen Volcanic National Park / Rebecca Latson

Step 6: measurements, Lassen Volcanic National Park / Rebecca Latson

Step 6: measuring the ear, Lassen Volcanic National Park / Rebecca Latson

Upon completion of processing, the animal is returned to the trap and after making a full recovery from the anesthesia, released back at their original trap sites.

How do they know which animal goes where? Those little yellow flags are numbered to correspond with the numbers painted on the traps, so it’s just a matter of matching trap number to flag number.