ESTIMATING
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Reprinted from:
North Dakota OUTDOORS September-October 2000
ESTIMATING
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By nature, hunters are inquisitive. They ask a variety of questions about the game they seek. What do they eat? When are they most active? How large is the home range?
After an animal is down, hunters frequently wonder how much it weighed when it was alive. However, scales are seldom available in areas where hunters usually tag and field dress big game animals.
While it is seldom practical to get a total body or live weight of a freshly killed animal, it is possible make an accurate estimate of live weight after measuring a dressed animal on a scale.
Over the past 40 years retired big game biologists Jim McKenzie and Jack Samuelson, as well as big game supervisor Roger Johnson and other North Dakota Game and Fish Department biologists, have collected weights and measurements on the six big game species found in North Dakota. By using the equations found in Table 1, and knowing the dressed weight - whole body or live weight minus internal organs - it is possible to derive a good estimate of an animal's live weight.
HOW IT WORKS
After determining the dressed weight of an animal, say a white-tailed buck, use the
appropriate equation listed in Table 1. If the buck weighed 150 pounds dressed, multiply
that times 1.15, and then add 11.7. The 184-pound-total is close to the true live weight.
The average and ranges of weights for each North Dakota big game species is highlighted in
Table 2.
TABLE 1 Equations for estimating live-weight from dressed weights of six North Dakota big game species (all weights are in pounds). |
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| Bighorn Sheep Ram - (dressed weight x 1.13) + 31.9 Elk Moose Mule Deer |
White-tailed Deer Doe - (dressed weight x 1.30) + 1.60 Buck - (dressed weight x 1.15) + 11.7 Pronghorn (Pronghorn data from G.J. Mitchell. 1971.
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TABLE 2 Average and range of fall live-weights in pounds for North Dakota big game species (all weights are in pounds). |
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| ELK Young-of-the-year: Average weight: 298 pounds Yearling and adult females: Average weight: 495 Range: 438 - 556 Yearling and adult males: Average weight: 698 Range: 469 - 950 MOOSE MULE DEER |
BIGHORN SHEEP Yearling and adult males: Average weight: 196 pounds Range of weights: 123 - 250 WHITE-TAILED DEER PRONGHORN (Pronghorn data from G.J. Mitchell. 1971. Journal of Wildlife Management. 35(1): 76-86) |
THE BIOLOGY BEHIND THE NUMBERS
To biologists, these equations are not just a string of numbers. They provide insight
about the animal and how well it was doing. For example, a heavier-than-average fawn
suggests the animal has had an excellent diet and could have reached puberty and become
pregnant at six months of age. A heavier than average doe, on the other hand, may suggest
she lost her fawn(s) for some reason and was not physically taxed by nursing one or two
fawns all summer.
These numbers also reveal differences in the make-up of each species. The internal organs of an average adult whitetail buck account for about 14 percent of its body weight. An average pronghorn buck would have 27 percent of its live weight allocated to internal organs.
The more muscular whitetail is built like a running back - a fast starter that tires quickly after about a quarter mile. The pronghorn's heart and lungs are larger than those of a whitetail, and contribute to its ability to run tirelessly at speeds up to 40 miles per hour for long distances, and much faster for short bursts.
BILL JENSEN is a North Dakota Game and Fish Department big game biologist.
NDGF
