Individual study: Effectiveness of multi-capture live-traps in the capture of brown rats Rattus norvegicus; a field trial in Surrey, England
Taylor K.D., Hammond L.E. & Quy R.J. (1974) The reactions of common rats to four types of live-capture trap. Journal of Applied Ecology, 11, 453-459
Removal of rats Rattus spp. may be desirable for conservation purposes. Brown rats Rattus norvegicus are comparatively difficult to trap, and in capture-recapture studies, some individuals subsequently show a pronounced tendency to avoid traps. The frequent failure to capture more than a proportion of rats in a population is often attributed to 'trap-shyness', which can be either inherent (i.e. traps avoided when first placed as unfamiliar with them) or could be learned. This field study examined the efficiency of trapping using two types of multi-capture live-traps.
Eight pairs of traps (one 'repeater' and one 'wonder' trap making up each pair) were used. Basic function and design are:
Repeater trap: The action of a captured rat passing through to the holding cage resets the trap for the next. It was constructed of welded wire mesh with a sheet metal bait hopper.
Wonder trap: This trap has a non-return door, the door opens allowing a rat to enter, but a counter-balance holds the door in the closed position preventing rats from exiting.
Traps were pre-baited with wheat grain for 6 weeks at a large sewage disposal site harbouring rats. The amount of wheat taken from the traps was recorded weekly initially, then daily. The traps were then set over 3 days and checked regularly.
Wheat consumption in both trap types increased progressively during the pre-baiting period, frequently all the wheat was taken from some of the wonder traps. When the amount of wheat available in the wonder traps was increased, the take from the repeaters showed a tendency to decrease, suggesting that rats were more cautious of the repeaters.
When the traps were set, the numbers of rats caught were at variance with the numbers estimated to have been entering during the pre-baiting period (9.4/day in repeater traps; 25.6/day in wonder traps). More rats than expected were caught in the repeater traps (average 4.0/day) and relatively fewer in the wonder traps (average 7.0/day). However, wonder taps were clearly more efficient at catching rats.
This result was at odds with trapping efficiency recorded for these two trap types when rats were confined in an 'observation room' (for a summary of this study see http://www.conservationevidence.com/EditEntry.asp?ID=911), where the repeater trap was more effective at catching rats than the wonder trap.