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Small Mammal Trapping Using Sherman Live Traps

Number: IACUC-GUID-010 

Responsible Office: Office of Research and Creative Scholarship (ORCS) 

Applies to: Principal Investigators Conducting Animal Research  

1. Purpose 

This guideline provides best practices for the humane and effective live trapping of small terrestrial mammals—including deer mice (Peromyscus spp.), voles (Microtus spp.), and jumping mice (Zapus spp.)—using Sherman live traps. Special emphasis is placed on mitigating the high mortality risk to shrew species (Sorex spp.) by incorporating supplemental food sources that support their high metabolic needs. 

2. Scope 

These guidelines apply to all field personnel involved in small mammal live-trapping for ecological, behavioral, or population-based studies conducted under IACUC-approved protocols. All trapping activities must adhere to relevant federal, state, and institutional regulations and ethical standards.  

3. Considerations 

IACUC discussions regarding the high mortality rates associated with by-catch of shrews (Sorex spp.) during the conduct of small mammal research utilizing Sherman Live Traps have concluded that accommodations should be made for this species to ameliorate associated mortality rates. 

• Shrews have extremely high metabolic rates and are especially prone to starvation in traps. Provision of high-protein food (10 g dried soldier fly larvae or mealworms) has been shown to significantly improve their survival. 
• Ensure traps are shaded and protected from direct sun or rain. 
• Minimize handling time and release non-target species promptly 

4. Procedures  

These are a general outline of trapping procedures and may vary depending on the approved Animal Use Protocol (AUP). The provisions for shrew survival (e.g., the addition of additional food source) is not optional unless justified and approved by the IACUC.  

A. Site Preparation and Trap Placement 

• Select representative microhabitats (e.g., forest floor, grassy clearings, edge zones) based on the species of interest. 
• Place traps level on the ground and stabilize to prevent tipping. 
• Space traps at consistent intervals (typically 10–15 meters) or as determined by study design. 

B. Trap Setup 

• Bait the trap using standard bait (e.g., a spoonful of rolled oats mixed with peanut butter). 
• Add 10 grams of dried soldier fly larvae or mealworms to each trap to provide an essential protein source for shrews and other insectivorous mammals. 
• Include a small slice of apple or carrot to supply moisture. 
• Place dry bedding at the rear of the trap to protect animals from cold, wet, or drafty conditions. 

C. Trap Timing 

• Set traps at dusk or late afternoon, when nocturnal and crepuscular species are active. 
• Check traps at dawn or within 1–2 hours of sunrise to minimize heat, dehydration, and predation risks. 
• In extreme weather (hot, cold, or rainy conditions), reduce trapping periods or suspend operations as necessary. 

D. Animal Handling and Identification 

• Gently transfer captured animals to temporary handling containers for identification, measurement, and any other approved procedures. 
• Wear gloves and handle all animals according to training and biosafety protocols. 
• Identify shrews immediately and release them as soon as possible if they are not target species or are not covered by the research permit. 

E. Post-Trapping Considerations 

• Re-bait and refresh moisture sources daily, replacing bedding as needed. 
• Monitor capture rates and non-target mortality; modify trap placement, baiting strategy, or duration if shrew mortality occurs. 
• At the end of the trapping session, remove all traps and associated materials from the field site. 

5. References 

1. Sikes, R.S. et al. (2016). Guidelines of the American Society of Mammalogists for the use of wild mammals in research and education. 
2. Scottish Natural Heritage. Nature. scot. Shrews: Trapping Guidelines 
3. J Gurnell & JR Flowerdew. Live Trapping Small Mammals – A Practical Guide. Mammal Society 
4. Churchfield, S. 1990. The Natural History of Shrews. Christopher Help. Pp 161-166 

6. Review, Approval and Version History 

Review and approval version history for this guidance

Version	Date	Description of Changes	Approved By
1.0	May 19, 2025	Initial policy creation	IACUC