Chemical immobilization of free-ranging fallow deer (Dama dama): effect of needle length on induction time

We evaluated impact of the needle length, sex, and body condition on chemical immobilization induction time in 50 (29 males and 21 females) free-ranging fallow deer (Dama dama) in Sweden, 2006-11. Induction time is probably the single most important factor when immobilizing free-ranging wildlife with the use of a remote drug-delivery system. Induction times should be short to minimize stress and risk of injury, and to ensure that immobilized animals can be found and clinically monitored as soon as possible. We measured the distance between the darting location and where we recovered the immobilized animal and also the time occurring between the two events. We used two types of needles: 2.0 × 30- or 2.0 × 40-mm barbed needles with side ports. The most important result is that a 10-mm-longer dart needle can reduce the retrieval time substantially (>20 min) until an animal is under monitoring. On average after the darting, the retrieval time decreased from 51 to 29 min and the distance decreased from 519 m from the darting location to 294 m. We suggest that a needle length of 40 mm is preferable for immobilization of wild fallow deer, especially for animals in over-average-to-fat body condition.