The breeding chronology of Louisiana deer can make aging challenging — but it can be done
Most of the aging work by deer biologists is done by utilizing the tooth replacement and wear techniques that were developed years ago by C.W. Severinghaus in 1949.
While this technique is not real accurate for older deer, it is less time consuming and for the most part is adequate for management work. Exact determination of age class based upon counting cementum annuli of incisor teeth is possible, but this is just not practical when one has hundreds of jawbones to sort through.
This early work by Severinghaus was based upon deer from the north, where the peak breeding month is November. This is the reason that ages are given in half-year increments: Deer bred in November will fawn in June, and fawns will be six months old in December during the hunting season. As deer move up into the older age classes, the adults also will be aged as 1 ½, 2 ½ and so on. The problem with Louisiana deer is that breeding in some parts of the state begins in September and continues into April. Consequently, with an eight-month breeding range, we also have an eight-month fawning range — so some fawns in December may be only a couple of months old. So as these deer grow older, the tooth replacement and wear will not follow the trends established by the aging studies, and can create problems for biologists.
However, it is certain that deer can be placed into specific categories, such as fawns, yearlings, young adults (2- to 3-year-olds), mature adults (4- to 6-year-olds) and old adults (7-year plus). This generalization is more than sufficient to calculate the necessary age and growth parameters for management purposes.
The following chart illustrates the breeding range in Louisiana, and shows how jawbones can vary in tooth replacement and wear during the hunting season.
The gestation period for deer is about 200 days, or seven months. A doe in Area 6 that is bred on Feb. 15 will give birth to a fawn on Sept. 15, and that fawn will be 2 weeks old when bow season opens on Oct. 1.
Consequently, the archery doe season is delayed a couple of weeks in Area 6 for this reason. But the fawn is still only 2 weeks old, and if the doe was to be killed the fawn would not likely survive. So many clubs and landowners delay the doe harvest even later.
September-born fawns in Area 6 will not be 6 months old until March. An Area 2 doe bred on Nov. 1 will drop the fawn on June 1, and that fawn will be 4 months old on Oct. 1. It will have lost its spots and be weaned and eating on its own, and would survive should a bowhunter harvest the doe. If both of these fawns were killed in January, the Area 2 fawn would be 6 months old and the Area 6 fawn would be a little older than 3 months, and the two jawbones would look different.
But both of these harvested deer would be classified as fawns and be grouped into that category, so it is really not a problem. The problem comes as these deer grow older and the eruption and wear patterns do not follow the typical pattern for that age class. Instead of looking at a jawbone for a 3 ½-year-old (42-month) deer, the jawbone will be several months younger, showing some characteristics for the 2 ½-year age class.
As one would guess, fawns are easy to age — their smaller body size equates to a smaller jawbone, which should be a dead give-away even to a novice hunter.
The typical fawn jawbone will have three temporary premolars, and one permanent molar. The third temporary premolar is the key for separating fawns and yearlings (1 year olds) from adults. This third temporary premolar has three distinct cusps, and will remain in place until it is finally replaced at around 18 months. The new permanent premolar will have only two distinct cusps. One should keep in mind that these temporary premolars will wear, and I have witnessed hunters opening the mouths of yearling deer, seeing these temporary worn out premolars and calling it an old deer.
As a fawn grows older, the second and third molars will begin to erupt and the deer moves into the yearling age class. The typical Area 2 fawn killed in November will have a jawbone with three temporary premolars and one fully erupted molar. An Area 6 fawn killed in December will have three temporary premolars and one molar that is not fully erupted. In some cases the molar may show the first two crests of the first cusp erupting, or the first cusp and the tops of the second cusps erupting.
Many clubs and landowners often avoid shooting fawns since they do not want to shoot nubby bucks, but a doe fawn is a good animal to harvest and it does not hurt the program to harvest a few nubby bucks and see what their growth rate is.
The average live weight for both the buck and doe fawn classes should be 60 pounds or better. Male fawns will weigh more than female fawns, and on good habitat and when herd conditions are right, some doe fawns may breed and give birth to a single fawn as a 1 year old. However, most of the Louisiana data will show that for the most part very few of our doe fawns breed. Most male fawns only produce a visible nub, the pedicel bone on which antler will grow, but in the early-breeding and fawning areas, some male fawns may develop a small bony antler peg.