Lecture 7: Surveying for small mammals

study design

how should you allocate your sampling in the field? - random? - systematic? - stratified? stratified random(equal vs proportional weighting)

toe clippings

in prairie voles - toe-clipping influenced recapture rate, esp for subadult animals - toe-clipped animals moved more than ear-tagged animals - no influence on rate of change in mass or in disappearance - reduces survival modestly in male meadow voles - survival marginally higher for naked mole rats with toe-clips vs those with implantable transponders - if carefully applied can be without any biologically meaningful effects

Grid trapping

presence/absence = yes abundance = yes (assumes all animals trappable) relative abundance = yes (assumes equal trappability) density = yes (but what is the area covered

Web Trapping

presence/abundance = yes abundance = yes relative abundance = yes density = yes webs: - relaxes strong assumptions of closure in most models - relaxes the need to know capture probabilities however, the ecological community has been slow to adopt webs - novelty and underlying mathematics - variable density of traps - variable impact of people walking - webs likely best in open terrain but less so in meadows, steppe, and other habitats with abundant ground-level vegetation

accumulation curves to determine sampling effort

- # of species documented as a function of... a. # of animals captured b. cumulative sampling effort

Modified Schnabel Method

- also extends L-P to multiple censuses - assumptions as in L-P but more rigorous, as the pop cannot change over a longer time period

other methods of marking small mammals

- hair clippings - UV fluorescent marking: injectable tattoo ink subcutaneously into the tail

trap placement

- how should you arrange your traps in the field? - transects? - grids? - webs? - equally important, how many traps should you use, and for how long should you sample? - species/ individual accumulation curves

what if a closed pop is unlikely?

- immigration or births? - emigration or deaths? - more refined estimators allow for estimation of survival and birth rates between sampling periods, as well as estimation of pop size - best know and most widely used: - Jolly-Seber - Cormack-Jolly-Seber (CJS) Jolly- Seber and other assume: - equal catchability of all animals - all marked animals are equally likely to survive - cause only marked animals are used to estimate survival rates, there is no assumption of equal survival b/t marked and unmarked animals - marks are not lost, gained, overlooked - all samples are instantaneous, and each release is immediate - full appreciation of J-S/C-J-S beyond the time we have here - implementation increasingly accessible.

basic rules of field biology

- never put yourself in danger - the animal always comes first(after you) - plan your meals and other events around the needs of your species - record your data clearly, carefully, thoroughly

principle approaches

- observational, e.g. line transects - tracking - photography - trapping: many types and approaches, focus today on trapping small mammals

transect vs grid

- pearson and ruggiero compared transect vs grid trapping - montana, 2 forest types, 2 yrs - transects yielded more captures, more individuals, and more species, than grids - differences between transects and grids tended to be greatest when small mammal numbers were lowest - transects appear to be more efficient than girds for small mammals, and provide better resolution of community structure for a given effort

handling small mammals

- removing from traps, applying ear tags or other marks, measuring, collecting blood or other samples - this is inherently stressful and THE MOST stressful time for your capture - you are big, smell predator - scruffing smaller species - body grip for larger species: observe breathing, potential for scent transfer - minimize handling time - minimize time to release - minimize sensory input - cover cages - place in a quiet, shady location

Lincoln-Petersen Index

- simplest mark-recapture method - one marking episode and one recapture episode, which must be a random sample - all marks may be identical Time 1: capture and mark M animals Time 2: capture C animals, of which R are marked Q: what was N - the pop size at Time 1? - assume the proportion of marked animals in the pop at Time 2 is equivalent to the proportion marked in the second capture assumptions as in MNKA - closed population - marks not lost, gained, overlooked - equal trappability - equal re-trappability - capturing and/or marking doesn't influence Pr(recapture)

transect trapping

- trap spacing may be fixed, semi-fixed, or variable - very useful for evaluating presence - particularly useful for learning where animals occur; the world is inherently heterogenous - also of value in obtaining relative abundances - if the perpendicular distance over which animals are attracted to traps is known, density could be measured - useful for species strongly tied to runways presence/absence = yes abundance = yes(assumes all animals equally trappable) relative abundance = yes (assumes equal trappability) density = yes (if sampling era can be defined which can be very difficult

4 groups of methods for sampling mammals

1) small mammals - most mammals are in this category (77%-87%) 2) large mammals 3) aerial mammals 4) aquatic mammals

trapping small mammals

1. pitfall traps - particularly effective for shrews and other very small species that may not trip the treadle on a live trap - can be very dangous 2. kill traps - fossorial beasties - macabee, conibear 3. snap traps - rats, mice, etc. 4. live traps - sherman (folding vs non-folding, aluminum vs galvanized, solid sides vs perforated) - tomahawk, mesh traps - different sizes for each but works good for chipmunks, fox/jackrabbit, squirrel, raccoon, skunk, mouse, cat - foothold traps: no teeth but often with offset or padded jaws, generally for larger mammals but also for fossorial taxa ; coil-spring traps, longspring traps 5. Indirect Sampling - hair snares: common for large carnivores, recent extension to small mammals, not used extensively with small mammals but potential is huge - automatic cameras

survey objectives

1. presence/absence only? 2. abundance a. absolute #'s b. relative abundance 3. density? - #'s per unit area additionally - spatial or temporal comparisons at multiple levels - population structure/composition - community structure/composition

what to do after traps placed

1. removal methods: catch-per-unit-effort(CPUE) = essentially, linear regression of CPUE vs total # removed - "effort" may be trap-nights, hunter days, etc. - may be useful if associated with regular removal efforts associated with management - CPUE estimates likely to be accurate and precise only if a large proportion of the population is removed Assumptions - closed population - equal detectability: all animals have equal probability fixed over time - all removals are known 2. Capture-recapture/Capture-mark-recapture methods - animals "captured" and marked in some manner - ear tags, toe clips, fur dyes or clips, ear tattoos, PIT tags, unique pelage patters

Schnabel extended this to multiple samples

N = estimated pop size M = # marked in study area C = # of marked and unmarked animals in sample area R = # of marked animals in sample

Estimating #'s with capture-recapture data

Raw #'s - total # captured - minor adjustment - minimum number known alive (MNKA) - still doesn't account for differential probability of capture/observation estimators - population closed(no gains[immigration, births], no losses [emigration, deaths]): lincoln-petersen index - no need for separate marks/tags - population open (may be gains and/or losses: Jolly-Seber, Cormack-Jolly-Seber