Assessing EDR and a novel deer repellent for reducing by-kill of white-tailed deer (Odocoileus virginianus), during aerial 1080 operations

A 2014 carcass search survey confirmed that Tiakina Nga Manu aerial 1080 operations, undertaken to protect resident mohua (Mohoua ochrocephala) from increases to predator populations following substantial beech (Nothofagus sp.) mast events, cause mortality for Wakatipu white-tailed deer. Non-target by-kill of deer generates significant public opposition to predator control operations. We assessed if a current deer repellent (EDR) and a repellent in development (Pestex-DR) were effective at repelling captive white-tailed deer from consumption of nontoxic baits, commonly used in Tiakina Nga Manu operations. Both repellents were found to significantly decrease bait consumption, and we observed clear displays of aversion to repellent baits by captive deer. Ten GPS collared wild white-tailed deer were then monitored following a Tiakina Nga Manu operation using EDR in 2016. One collared deer was poisoned following the operation, confirming that EDR is not 100% effective. We recommend the most effective available deer repellent be used for future Tiakina Nga Manu operations over the Wakatipu white-tailed deer habitat to minimise public opposition to these predator control operations. In addition, our results suggest that differences in the boundary size and shape of operations may account for some of the variability in non-target by-kill observed between studies.