Professor Bob Giles suggests that hunters and other outdoors people become actively involved with making precise observations in the field and then doing something with the results. "Seeing stuff" is not enough, he claims. The following note suggests what to do with some of the number from the wilds.
Observe fawns; observe does. Count them. How many fawns are there per doe? You or your hunting crew use 3 periods, at least July, September, and November. Convert the numbers to the percent of the does that have at least one associated fawn. What is the rate of decline? e.g., if 99, 53, 32 over 3 periods.
The linear regression from such data is for estimating fawns (F)
F = a - b (time).........Equation 1
F = 128.33 - 16.75 T.
the decline rate is -16.75.
The R-square or index to the quality of the equation is 0.96, about as good as field data will yield.
Taken separately, declining from a previous amount, the rates appear to be:
(99 - 53)/99 = - 0.46
(53 - 32)/53 = - 0.40
Graphically, we can project the line to the origin or just use the value of "a" in Equation 1, that is, 128 fawns may have been the total that were born.
Based on what we know about the herd potential, the likely food next year, or other factors, we can decide whether the estimate of the original production of fawns (fetuses) was realistic or not and whether our fawn-to-doe ratio observations were accurate.
The estimates of fawn mortality have to be based on field estimates of fawns with doe deer. Over a 4-6 month period, does also may die. The fawns-per-doe estimate early in the year may be changed by the death of both fawns and does during the year, but at different rates. The number for the percent at the end of the year (e.g., 32) may be too large.
An R* DEER program (RDeer 020) will soon be available to download to explore these relationships.
In superior habitats, the mortality of all animals may be about the same, but generally fawn mortality is high ... as much as 70%.
What's the bottom line? Fawn mortality, a critical element in almost all deer population analyses, is a number difficult to get and rarely do deer managers have an adequate sample size. Past estimates have been flawed because they used available ratios, did not use appropriate regression, and did not include doe mortality. There's much work ahead for the modern deer resource manager.
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Giles, Jr.
Last revision January 17, 2000.
