SMALL MAMMAL TRAPPING PROTOCOL
ARIZONA 2008
Updated 2/06/08
Purpose of study The purpose of the small mammal trapping study is to see how large herbivores (Rocky Mountain Elk, Mule Deer, and White-Tail Deer) influence small mammal population dynamics. Because many small mammals are nest predators, changes in small mammal populations may influence nest predation rates. A few studies show that when large herbivores are excluded, small mammal populations may be dramatically influenced. For example, a study in East Africa by Felicia Keesing showed that pouched mouse density was twice as high inside of ungulate exclosures as outside. This last season (2007),after the exclosures had been up for 3 years, we began to observe changes in the small mammal communities: we found higher densities of rats and mice inside of our exclosures, and higher densities of chipmunks outside. We will continue to use the data collected with this study to determine how small mammal populations change with the exclusion of ungulates, and we will also look at whether small mammal survival and habitat occupancy is influenced. Because small mammals are important prey for a diverse group of predators, and because they are important seed predators and dispersers as well as nest predators, understanding how ungulates influence small mammal populations may be one important aspect in determining how large herbivores structure ecological communities. Elk exclosure (E) and control (C) plots There are 3 paired exclosure and control plots. PLOT: 12 (E) & 11 (C) PLOT: E4 (E) & E3 (C) PLOT: 14 (E) & 8 (C) Each pair is in a single canyon, but in separate snowmelt drainages. Because they are relatively close together, (< 1 kilometer apart), we can assume that microclimate conditions (rainfall, cloud-cover, etc.) are similar. General info On each plot there is one small mammal trapping grid ~250 meters long and ~100 meters wide. Entire plots are roughly 9.75 hectares in size (150 m x 650 m), and the small mammal trapping grid is located roughly in the center of the plot. The grid is marked by small plastic pink flagging and in addition there is rebar covered with plastic piping on opposite ends of the drainage to mark the ends of the grid. The grids are centered at the bottom of the drainage (Center of plot, X‟s above), and rise up each side of the drainage towards the ridges. There are 10 Sherman live-traps 10 meters apart from one another
along the 100 meter width, continuing for 25 lines (total of 250 Sherman traps/ grid). On each flag is marked the trap station which is a combination of a letter and number. Down the length of the drainage (25 lines), flags are marked A through Z, and across the width of the drainage, (line of 10 traps) flags are marked 1-10. There are also 26 Tomahawk (Havahart) live-traps set throughout the grid.
650 m
O O O O O O O O O O O O O O O O O O O O O O O O O
150 m
X X X X X X X X X X X X X X X X X X X X X X X X X
O O O O O O O O O O O O O O O O O O O O O O O O O
Graphical X = permanentof a plotmarker representation station with small mammal trapping grid in center. = perimeter of rodent sampling grid (90m x 240 m) O = Transect of vegetation sampling subplots Center of plot
R I D G E
10 m
R I D G E
There are 20 Sherman live-traps on the diagram below, but imagine it continuing on… Small mammals at field site The small mammal species in the study system include gray-collared chipmunk (Eutamias cinereicollis), Mexican wood rat (Neotoma mexicana), Merriam‟s shrew (Sorex merriami), rock squirrel (Spermophilus variegatus), brush mouse (Peromyscus boylii), deer mouse (Peromyscus maniculatus), long-tailed vole (Microtus longicaudus), golden-mantled ground squirrel (Spermophilus lateralis), red squirrel (Tamiasciurus hudsonicus), tassel-eared squirrel (Sciurus aberti), valley pocket gopher (Thomomys
bottae), black-tailed jackrabbit (Lepus californicus), and eastern cottontail (Sylvilagus floridanus). Deer mice, brush mice, woodrats, and chipmunks are captured in traps most often. Voles and shrews are rarely captured, and tassel-eared squirrels, gophers, jackrabbits and cottontails are almost never captured. Sherman traps The Sherman live-traps we use are small and designed to catch deer mice, brush mice, chipmunks, voles, shrews, and small woodrats. When setting up the Sherman traps, insulation foam is attached to a trap with a rubber-band. This prevents the inside of the trap from getting too hot or cold and keeps some rain out. Then, a small hand-full of polyester fiber-fill is placed inside of each trap. This adds insulation and can be used by the rodent to build a nest to keep warm. Traps are placed within a couple feet of the pink trapping flags and are placed either level with the slope, or with the doors facing slightly down hill. If the trapping flag is in direct sunlight in the open the trap are placed in the shade of a rock or plant next to the flag and bark or leaves may be placed on top of the trap to help in shading. If snow is present, it‟s not a problem to set up the traps on top of the snow.
Tomahawk traps The Tomahawk traps are larger and designed to catch large woodrats, red squirrels, rock squirrels, and rabbits. Tomahawk traps are covered with a large piece of insulation foam and this is held on by a large rubber-band. No polyester fill need be placed in these traps. Tomahawk traps are set out every 3rd and 7th station across the width of the drainage, and every other line down the length of the drainage.
Bait
Sherman traps: Rolled oats (bought at a feed store) with a slight peanut butter scent. To properly place bait in a Sherman trap sprinkle a small handful of oats on the front and inside the back of the trap. Tomahawk traps: Use unshelled peanuts. Toss onto trap trigger 5-6 peanuts. Trapping schedule We will have 3 trapping sessions throughout the field season. One will be in May, one in June, and one in July. Paired treatment and control plots are trapped simultaneously. So, for example, we will trap plots 8 (Control) and 14 (Exclosure) simultaneously. Plots are trapped for 4 trapping nights and are checked twice daily, early in the morning around 7am, and then again in late afternoon around 3 or 4pm. Checking traps twice during the day reduces mortality (animals spend less time in traps), and allows processing of both nocturnal and diurnal animals separately. An example of a schedule would be: set out traps on a paired plot on a Monday. Open and bait traps Monday evening. Then, check and process traps on Tuesday, Wednesday, Thursday (4 trap nights), and Friday morning. On Friday morning, as traps are checked they can be closed. After animals on both paired plots are processed, traps can be picked up, cleaned, and transported to the next paired trapping plots. Once all paired plots have been trapped (all six plots), this will be equal to one trapping session (this takes about 3.5 weeks). It takes about 2 days to pick up, clean, and relocate traps. General safety Because both deer mice and brush mice are reservoirs for the Sin Nombre Virus (Hanta virus), the use of respirator masks and latex gloves is mandatory while processing mice. Other safeguards include: holding animals away from the body while processing so that scat and urine do not get on your clothes, spraying gloves with an alcohol – water mixture after each handling and replacing gloves if they are ripped, torn, or get scat, urine, or blood on them, washing hands thoroughly after trapping, and finally, changing clothes at camp and leaving trapping clothes outside the tent in the sunshine. Small mammal trappers should get a “fit test” at Northern Arizona University to make sure the respirator mask fits and works properly before the start of trapping, and masks should be disassembled and cleaned occasionally (every couple of weeks) with soap, water, and/or alcohol swabs, and facial hair should be kept to a minimum throughout the trapping season as it can interfere with the fit of the respirator. Every time the mask is put on the trapper should test the fit of the mask by covering the air filters with both hands and trying to breathe in. A mask that is on properly will not allow breathing with the filters covered. Trapping supplies and equipment that potentially come into contact with mouse feces, urine, or blood should be transported in the back of the truck (not in the cab), and kept outside of the tent. Furthermore, do not eat while trapping! Wait until you have returned to the truck and thoroughly washed your hands with soap and water. A bar of soap and water container with a spigot as well as hand sanitizer should be in the truck at all times. ALWAYS USE GLOVES AND RESPIRATORS WHEN HANDLING THE ANIMALS!
Logistics Because there are two small mammal trappers, it is easiest to divide up drainages into two sections of responsibility: the left half (stations 1-5) and the right half (stations 6-10). Trappers can then walk the trap-line on their side of the drainage (not have to traverse the entire drainage which takes more time) and get to know the trap lines better: if you are consistent then it is easier to find traps as the understory fills out during the summer. There are two-way radios that can be used to maintain contact in case help is needed. As you walk the trap line you will notice Sherman traps with closed entrances. These are either closed with nothing in them (wind, trap was too sensitive, an animal escaped, or an animal kicked it), or have one of the smaller mammals in them. If closed, pick up the trap and look inside by opening the door slightly (not enough for the mammal to escape). You should be able to tell whether the trap is occupied or not, and what the species is. Your choice of equipment for that particular trapping station will depend on what species it is and how large the animal is. Equipment Each time you go trapping you should have the following equipment Backpack containing the following: Respirator mask latex or vinyl gloves (5-6 pairs) (to handle smaller mammals with) work gloves (to handle larger mammals with) plastic bags (to process smaller mammals in) cloth bags (pillow cases) (to process larger mammals in) small metal ear tags: (for use on: deer mice, brush mice, chipmunks, voles, shrews) large metal ear tags: (for use on: woodrats, red squirrels, rock squirrels, rabbits) Small metal ear tagger Large metal ear tagger 3 Pesola Weight scales (one for smaller, one for larger mammals), a 60 g scale, a 100 g scale, and a 300 g scale Bag of oats (for refilling Sherman traps) Bag of unshelled peanuts (for refilling tomahawk traps) A Dozen data sheets for recording data / clipboard Write-in-the-rain Journal (for recording data while it is raining) A work journal (for recording natural history observations) A couple of mechanical pencils A couple of small and large zip-lock bags for mortalities A black sharpie (for writing info on these bags, for rewriting station number on flags where it has worn off) A Two way radio (charged the night before) Small spray-bottle with alcohol-water mix Small bottle hand sanitizer
Extra rubber-bands (large and small) Extra insulation foam pads, Extra polyester fiber-fill Small and large ruler for measuring body length Have in Truck Accessible to bring out to field as needed Large measuring tape (in case flags need to be repositioned if they are kicked by an animal) Extra flags Extra rubber-bands Extra insulation foam Extra polyester fiber-fill Extra Sherman traps & Tomahawk traps (in case they break) Soap, water, and hand sanitizer (to wash hands after trapping) Mice, voles, shrews, and chipmunks (Sherman Traps) If you see that the Sherman trap has an animal in it, close the trap door, put it down, put on gloves and respirator, and lay out the equipment you need. When you look to see if the trap is occupied, try to see if it has an ear tag already. Lay out the new tag, ear tagger, the appropriate scale (Pesola), data sheet and clipboard, and pencil so you are ready. Holding the trap upright (trap-door facing towards the sky), place the plastic bag around the four corners of the outside of the trap around the outside of the trap-door. With the bag in place, open the trap door, then turn the trap upside-down and the animal will fall into the plastic bag. You may have to shake the trap lightly. Close the bag and weigh the bag and animal using the scale (Be sure to weigh the empty bag when done). Then, grab the animal in the plastic bag by the nape of the neck through the plastic bag, and „unwrap‟ the bag from around the animal. Put the ear tag at the base of the ear. (Ear tags placed at the outside edge of the ear may come off and rip the ear). Also, be sure to place tag on right ear. This makes it easier to look for when you slightly open trap to see if it is occupied. Always do the ear-tag first and record the ear tag number of the data sheet for proceeding – if the animal escapes the tag is the most important thing to have done. Woodrats, Squirrels, Rabbits (Tomahawk Traps) If a Tomahawk trap has a woodrat, squirrel, or rabbit inside, approach trap quietly and respectfully (a couple animals may have died in the past because they were overly stressed out). Get out the cotton bag (pillowcase), leather work gloves, large metal tag and large ear-tagger (if new capture), clipboard with data sheets, and pencil. Put on the leather gloves, place the opening of the pillowcase over the trap door, open the door and wait. The animal should come running out of the trap into the pillowcase. Then zip the end of the pillowcase closed and weigh the animal and pillowcase with the scale and record the weight in your journal. (Don‟t forget to weigh the pillowcase afterwards) Then, open a small hole with the zipper; direct the animal towards the small hole where just their head will fit outside. Holding the animal down by the nape, tag the ear, then
flip the animal over, pull back the pillowcase farther, and determine the sex, breeding condition, and presence of scars and parasites. Before you leave the trapping site after you let the animal go, always make sure you pick up all of your equipment! Recording Information Trapping Session (1, 2, or 3) Date (e.g. 5/06/08) Plot (11, 12, E3, E4, 8, 14) Trap Station (letter and number) Trap Kind (Sherman = S, Tomahawk = T) Time of day (AM or PM) Species (DMSE = deer mouse, BMSE = brush mouse, CHP = chipmunk, RAT = woodrat, SHREW = shrew, VOLE = vole, ROCKSQ = Rock Squirrel, REDSQ = Red Squirrel) Tag # (Should have four digits- sometimes part of the ear can cover the 1st digit), if so, reposition. You may have to clean the tag as well. Weight (in grams) Sex (determined by size of genitals and their distance from anus, and presence of mammary glands) Age Class (Based on pelage color, divide into juveniles, sub-adults, and adults) Reproductive Condition (Females: 0 = non-breeding no swelling, 1 = Genitals slightly swollen, 2 = Pronounced swelling in genitals). Also record whether female is lactating (mammary glands not swollen = 0, slightly swollen = 1, swollen = 2, (Males: 0 = nonbreeding, 1 = testes slightly descended, 2 = testes fully descended). Capture Code C = Trap Closed, nothing in it. (Also put C if trap is missing (try to find it! Write down when it disappeared and where you found it (if you did)), or damaged (if damaged, replace trap and bring damaged one back to camp). N = New Capture (Put this if animal has no ear tag. Occasionally animal will have a ripped ear which means that the ear tag may have ripped out. Still put “N” in this case, just record in notes that ear is ripped (record which ear) and you suspect it might be a recap. Then put tag on unripped ear. If you feel that an ear tag in place is about to fall off, put an ear tag in the other ear and record in notes the new number and what ear it is on. R= E= Recapture (If animal already has an ear tag). Escape (Only write escape (E) if you were unable to put an ear tag on the animal and it gets away. If it‟s a recapture but gets away before you have a chance to read the number,
put escape (you can say in notes that it had an ear tag and is a recapture). If you put an ear tag on it (or read the number), record the number and the animal gets away, put either N or R and you can say in notes, for example: escaped before weight was determined, etc. Mortality (Y = Dead, N = Not Dead. If animal is in bad shape- not moving much but still breathing, write N (not dead) but write that it wasn’t doing well in the notes.) Measurements (take in mm: Take body and tail measurements while it is in the bag) Tail length Body length Right Hind Foot Right Ear Distance traveled (Watch where animal goes when you let it go. Estimate how far it travels (in meters) after you let it go before it either disappears from sight (behind a tree), or disappears into a log, tree, brush pile, hole, leaves, etc.) Health (Record whether you see parasites, what kind they are (if you can tell), i.e. ticks, mites, fleas) Scars (Possibilities are ripped ear, end of tail missing, eye damaged, etc.) Weather (Write down the weather and temperature for the 6 hours prior to trapping: so if its morning, try to remember what the weather was the last night (did you notice water puddles on the ground?) Was it really cold when you went to sleep and woke up? Notes (Anything listed above that needs to go here, general observations, etc.) What to do with mortalities If you suspect a trapping mortality, try to make sure the animal is actually dead. Using the precautions listed above (respirator, gloves, etc.), take the animal out of the trap, see if it is cold to the touch (most mortalities are due to hypothermia – which may be the result of being in a cold trap for too long without enough food and the ability to get warm through moving around), if it is stiff, and if its chest rises and falls with each breath or not. If the animal is dead, record all of the information as you would normally. If it‟s a new capture, take a new tag, record the number and then dispose of the tag (don‟t put the tag on the dead animal‟s ear, just crimp it and put in it a small plastic baggie and throw it away when you get back to camp). This way all animals will have a unique capture number which is helpful later in analysis. Put the animal in a zip lock bag and use the sharpie to write on the bag the trap session, date, species, plot, trap station, and ear tag number. Return animal to camp and give it to the trapping supervisor. Sometimes the animals are so cold that they appear to be dead but are still alive. After putting the animal in a bag and recording all the information, check on it periodically – sometimes you will find them breathing heavily in the trap as the oxygen runs out. In this case, find
a warm pocket, fill it with fiber-fill, and try to get the animal to warm up. Sometimes animals revive after spending thirty minutes in a warm pocket. Always return a revived animal to the same trapping point at which it was captured. If an animal sustains a lethal injury it may have to be put to death according the Animal Use and Care protocol (Animal Use and Care Committee, University of Montana). The procedure simply involves putting the animal into a plastic bag with a cotton swab soaked in isoflourene. This will put the animal into a deep sleep. Then, put the animal face down on the ground and sever the spinal cord around the neck by pressing down hard. The trapping supervisor will train you how to do this. Cleaning traps While you are trapping you will find traps that are very dirty from either blood or feces. Take these traps back to camp and replace them with new traps at the station that you took it from. These “dirty” traps will be cleaned after each trapping period (i.e. after all trapping is done at stations E3 and E4) so that they can be used the next trap period. To clean them, traps are soaked in a water-bleach solution, then scrubbed clean with brushes and allowed to dry open in the sun. Broken traps can be cleaned and put in a pile near camp to be taken back to Montana to be fixed. Woodrats will often gum up the trap the most from their feces. If a trap is not that dirty, leave it out in the field. Data entry You will be recording trapping data onto data sheets and then transferring this data onto summary data sheets back at camp. It is important to do this as soon as you can after the trapping is finished! As time goes by you may forget what the small notes that you recorded in the margins of your journal meant. Therefore, try to get all of this data transferred to master data sheets at the end of every day. It does take a little time and you don‟t want to let it build up and then spend half of a day transferring un-entered data. The summary data sheets allow us to get a quick sense of whether we are seeing changes in small mammal populations. The regular data sheets will be entered into program SPSS during the fall or spring. Work Journal You will be given a work journal to record weather and other natural history observations including species interactions, animal diets, strange occurrences, and any and all observations that you think are relevant to understanding how the ecosystem works and how small mammal populations might respond to an ungulate exclosure. While you are in the field you will learn an incredible amount about small mammal ecology and behavior and this will help you understand the behavior and ecology of their predators as well as the ecology of their prey. Write down observations you make about the environment that you think will be useful. For example, if you didn‟t catch very much that morning, but you know that it rained all night long, write this down. If you didn‟t catch very much and you remember that the moon was full the night before, write that down. If you observe any of these mammals doing anything interesting, eating anything
(not oats!), behaving in a peculiar way, or interacting with other individuals or other species in interesting ways, write that down as well. All of this information can be very useful later on (you will be asked to turn in your journal at the end of the season (so think of it as your work journal, have a separate personal journal if you want)). For example, last year I noticed that woodrats love to eat violet. Because we trapped more woodrats on exclosures than controls during the summer of 2006, increasing woodrat populations due to herbivore exclusion may lead to effects on plants. So next summer I will look for the effects of browsing on violet! Research Books There will be a collection of field guides you can look at in one of the work tents. We think we have the species identification completely figured out, but you still may catch an animal we haven‟t seen before. If so, take careful notes and measurements and come back and look it up! The Mammals of Arizona book and Peterson‟s Mammals of North America are both appropriate guides for this kind of thing. Trapping Training Schedule The small mammal trapping supervisor will train you for the first couple weeks of trapping. Because it will take longer to trap while you are being trained, expect an early rise and trapping to begin as soon as it is light enough to see inside of the trap. You will be trained how to do everything that is in this protocol so that you can confidently trap any and all animals you might catch. After the training is over you and your trapping partner will be expected to run the operation and you can report back to the trapping supervisor if you need to back at camp. Also, someone who is familiar with trapping will be able to take your place temporarily if you get sick. Final reminders Trapping is hard work, but fun. I have learned an incredible amount about the natural history of the area through research and careful observation. For example, last year I watched rock squirrels forage on violet seeds only a few feet from me. I noticed that they left a trail of violet seed parts and after examining the pile I began to see them everywhere. So be efficient while you work, but don‟t forget to take a breath, look around you and take in the beauty, and above all have fun!!!