Optimising Small Mammal Trapping by Considering Environmental Factors

Student Spotlight - Luke Owen

Undergraduate Research at the University of Lincoln

Email: lukehowen1999@gmail.com   LinkedIn: linkedin.com/in/luke-owen-310057181

I recently completed a BSc in Zoology at the University of Lincoln where I conducted my dissertation research on investigating which environmental factors affect small mammal trapping success.

Background

Live trapping is a useful method of monitoring the activity patterns of smaller mammalian species and determining population estimates, which are key for informing potential intervention to conserve vulnerable and endangered species (Hensbergen and Martin, 1993). Trapping quality and accuracy are optimal when the probability of capture is relatively high for the species of interest; something which could be affected by a range of environmental variables. For example, activity and trapping likelihood of small mammals have been shown to be strongly influenced by weather conditions across the globe (LaHaye et al. 2004). It is therefore important to consider weather conditions as covariables in population estimates as conditions favourable to an individual species could maximise the capture probability and precision of any population estimates (Lebreton et al. 1992).

Project & Fieldwork

My research project aimed to investigate how various microhabitat, macrohabitat, overall landscape factors and weather conditions affected the trapping success of four sympatric small mammal species: the bank vole (Myodes glareolus), field vole (Microtus agrestis), wood mouse (Apodemus sylvaticus) and common shrew (Sorex araneus).

The live trapping took place over the course of 3 months from July 2019 to September 2019 in various locations throughout Lincolnshire, predominantly grassland habitats and Lincolnshire Wildlife Trust protected sites (Figure 1). This meant 5am starts to collect the traps and take data measurements and late-night travels to set them again (the joys of field work)!

Between 30-50 Longworth traps, filled with all essential bedding and food, were set in preapproved regions at each location and marked with a bamboo pole with orange tape, to ensure they could be located and collected 12-14 hours after they were set. As well as recording the species caught in each trap, a myriad of habitat variables were recorded at each trap location. Microhabitat factors were recorded within a 50 cm radius and microhabitat factors within a 3 m radius. Habitat variables measured were: the average height (in cm) of vegetation; the density of vegetation (using an A4 chequered cardboard sheet divided into 10 equal squares and recording 4 measurements: north, south, east and west of the trap location, determining what percentage of the sheet is obscured); the inclination at the trap location (measured using a clinometer); and plant species richness.

Following this, overall landscape features were recorded with the habitat type and transition of habitat recorded at the site. The distance (km) to man-made structures (roads) and a water source were measured using online satellite imagery. Finally, the overnight weather conditions for each trap night at each location were recorded, including temperature (°C), lunar phase, precipitation (mm), duration of moon presence (minutes) and illumination from moonlight (%). A large number of variables were recorded (just over 16,000 individual data points), which I analysed in R to determine which factors influenced the trapping success of each species.

Results & Further Research

I found that trapping success for each species was influenced as follows:

• Wood mouse: most significantly influenced by an increased distance to man-made structures and a warmer overnight temperature
• Bank vole: also found to be influenced by warmer overnight temperatures as well as the gibbous lunar phase
• Common shrew: most significantly influenced by cooler overnight temperatures and the gibbous lunar phase
• Field vole: the gibbous lunar phase was found to have the highest relative importance for trapping success, but no recorded variable was found to have any statistical significance (possibly due to a smaller sample size of this species)

The findings of my study demonstrated the strong effects that weather and habitat conditions can have on trapping success. The exact response to these variables appeared to be species-specific, thus making the appropriate conditions for each species potentially useful as covariates for maximising capture probability in population estimates.

To build on this research, it would be interesting to look as well at intraspecific variations in small mammal species (Maher and Burger, 2011) by determining which habitat factors affect small mammals in other geographic regions, and whether these correspond to my results from Lincolnshire. This could be beneficial for population analysis as potential variations in optimal conditions could be applied to the timing of the trapping in order to maximise capture probability and the precision of population estimations.

Thank you for taking the time to read about my research in this blog. I would be happy to answer any of your questions (email: lukehowen1999@gmail.com).

 

Acknowledgements

I would like to thank Dr. Carl Soulsbury for supervising and supporting me through all aspects of this project. I would also like to thank Ellie Smith and all those who volunteered to help with data collection, I couldn’t have survived the mornings without you! You can read Ellie's own student blog about her research on harvest mice here.

References

Bruce Jones Design Inc. (2010) Printable, Blank UK, United Kingdom Outline Maps Royalty Free [map]. Available from https://www.freeusandworldmaps.com/html/Countries/Europe%20Countries/UnitedKingdomPrint.html [accessed 16 December 2019].

Hensbergen, H. and Martin, S. (1993) Climatic factors affecting trapping success of some South African small mammals. South African Journal of Wildlife Research, 23, 87-94. https://hdl.handle.net/10520/EJC116928

LaHaye, W.S. Zimmerman, G.S. and Gutiérrez, R.J. (2004) Temporal variation in the vital rates of an insular population of spotted owls (Strix occidentalis occidentalis): contrasting effects of weather. The Auk, 121,1056–1069. https://doi.org/10.2307/4090475

Lebreton, J.D. Burnham, K.P. Clobert, J. and Anderson, D.R. (1992) Modelling survival and testing biological hypotheses using marked animals: A unified approach with case studies. Ecological Monographs, 62, 67-118. https://doi.org/10.2307/2937171

Maher, C. and Burger, J. (2011) Intraspecific variation in space use, group size and mating systems of caviomorph rodents. Journal of Mammalogy, 92, 54-64. https://doi.org/10.1644/09-MAMM-S-317.1