Biological Bull’s Eye: Practice Makes Perfect with Dart Guns by Regional Wildlife Biologist Chuck Hulsey

June 3, 2015 at 10:26 am

A young bull moose enters a small Maine city.  It is confused and scared.  Refuge is found in an alley between two stores and he won’t leave. It appears healthy and non-threatening, but hanging around the side entrance of the store may not be good for business. Regional wildlife biologists are experienced and well trained in handling such situations and do so on a fairly regular basis. Last Wednesday many of our regional wildlife biologists met in Old Town for a joint practice with the various types of dart projectors (“dart guns”) we utilize.  It was also a good time to share ideas about the gear we use for both capture and animal care. Mobility is important when access requires transport by foot, ATV, or snowmobile.  But first a little background before going to our dart projector practice. [caption id="attachment_683" align="aligncenter" width="340"]A young and very tangled bull moose, which was chemically immobilized and freed  by Regional Wildlife Biologist Bob Cordes A young and very tangled bull moose, which was chemically immobilized and freed by Regional Wildlife Biologist Bob Cordes[/caption] There are two ways to capture a free ranging wild animal.  One is physical restraint. We have noose poles, cage traps, and nets for that purpose.  This strategy is preferred when the animal can be caught and handled safely. The other method is chemical immobilization (drugging).  Chemical immobilization is used on free-ranging wildlife for research, management, or rescue. What you see on TV has little resemblance to the actual use of drugs to capture and handle wildlife. First, biologists don’t use tranquilizers as the sole immobilizing agent. Valium is a tranquilizer with no immobilization value. Any biologist using a tranquilizer drug on a grizzly bear would become a former wildlife biologist in a matter of seconds. If used on an alligator, the biologist would go through the rest of his/her life with the colorful nickname like ”Lefty”, “Stubby”, or “Stump”. The drugs we use are in a class called “Dissociatives” which distort the animal’s perception of sight and sound, and most importantly, disengages the animal’s ability to use voluntary muscles: like those attached to jaws, claws, and powerful legs.  Another deviation from Hollywood is that it normally takes an animal as much as 10 minutes to go down, plus several hours for full recovery.  So as you can imagine, a moose next to a river is a bad situation. A moose next to the Interstate is worse.  These animals do not go down then merrily skip away during the time it takes for a beer and truck commercial. It gets more complicated.  The effectiveness of the drug can be compromised significantly if the animal is under a lot of stress. So, the animal’s condition and safety, and obviously human safety, are taken into account before the use of drugs can be an option. We all pack a reference book having the recommended drugs and dosage for many hundreds of species of wildlife, from white-tailed deer to warthogs (really). We almost always use a combination of two drugs to achieve: 1) immobilization, 2) a light level of anesthesia, and 3) an analgesic effect to eliminate any pain associated with use of darts. Once under anesthesia, respiration, temperature, and heart rate are closely monitored. The drugs can affect the animal’s ability to thermo-regulate so we are prepared to keep them calm (eyes covered) and cool or warm, depending on environmental conditions. A weight is needed to calculate the correct drug dosage. The vet places your dog on a scale to get an exact weight. Put a biscuit on the scale and my lab will knock you over to get to it. However, it is much harder to get a free ranging moose to step on a scale (plus you’d need four).  So we must estimate the weight by eyeball, but do have helpful experience to rely on. First, we see a lot of moose weighed at hunter registration stations, plus we already know average weights of a Maine moose by age-class (calf-yearling-adult). Second, the drugs we use are forgiving, so a close estimate works fine. [caption id="attachment_682" align="aligncenter" width="256"]Regional Wildlife Biologists Sarah Spencer and Bob Cordes load a practice dart though the end of the stock of a X-Caliber Pneu-Dart CO2 rifle projector Regional Wildlife Biologists Sarah Spencer and Bob Cordes load a practice dart though the end of the stock of a X-Caliber Pneu-Dart CO2 rifle projector[/caption] If you have anesthesia for surgery, doctors know your medical history and condition before they operate.  A slight sedative calms you down and you are in a clean and safe location. Everything is explained to you. The drugs used for your anesthesia are delivered intravenously or by mask. You drift into a plane of unconsciousness called anesthesia. Chemical immobilization of free ranging wildlife has the very same goal.  However, our patient is afraid, dirty, and most likely believes something big and scary is trying to harm them. Our drug must be delivered either from the end of a long pole (syringe pole) or from a dart flying through the air.  In either case the biologist must deliver the drug to the upper part of a rear leg, all while the patient is fully aware that nothing is going right in their world. We practice with our dart projectors because of the multitude of variables associated with delivering a drug dosage through the air.  First, dart size varies by dosage, which varies by species, which varies by weight. Drugs come in different concentrations (strength).  Higher concentrations (higher cost) equals smaller volume, which equals smaller dart. We highly prefer small over large. Darts range from about two inches to about eight inches long though size is actually measured by capacity. Another major variable is distance to target, which changes if the animal moves. Projecting the dart is accomplished by a powder charge or by CO2.  Projecting a dart with a charge introduces two more variables.  First is the power of the charge, of which there are four options. Our projectors (rifles) use a charge, but also have a selector with five ports allowing five different levels of gas to reach the dart.  So each charge (tell by color) has up to five options for power and distance.  Some of us also have dart projectors which rely on CO2 gas so the power of delivery is selected solely on the adjustment of PSI (pounds per square inch) on a dial.  This not only eliminates several aforementioned variables, the power setting can be changed on the fly if the distance to the animal changes. As if this weren’t complex enough, the trajectory of the dart needs to be lobbed on a slight arc so that the energy of the dart is diminished and does not injure the animal we are trying to help. Only 10% of the animal are an appropriate target, to which we are delivering a drug not a bullet. It is a responsibility and a challenge which most wildlife biologists put near the top of their most enjoyable jobs.