Wildlife Matters

A brief introduction is in order. I was the Area Wildlife Manager for MN D.N.R. from 1969-2000. For much of that time I had a weekly (to occasional) column in the News-Herald on matters pertaining to wildlife. People in this area have always had great interest in wildlife and nature in general. I intend to write mainly about wildlife topics that I hope will be of interest to others. This will not necessarily be a weekly column as many of us have found that retirement is a very busy job. The first few columns will be on antlers. Much of the information will come from scientific studies published in the book “Antler Development in Cervidae”, Caesar Kleberg Wildlife Research Institute.

Antler development

Many people use the terms antler and horn interchangeably, but they are quite different. Antler is bone which is grown and shed annually whereas horn is keratin (the same material as hair, feathers, beaks, claws, etc.) which forms a hollow sheath over a bone core and is not shed, except for our pronghorn antelope which does shed the hollow sheath each year. Unfortunately, the term “forkhorn” is commonly used, rather than “forked antler”, when referring to an antler with 2 points.

Antlers fascinate many people, both hunters and non-hunters. Shed antlers are available to be found by anyone, whether they are looking for them or not. Large antlers can be spectacular, but small ones also can be very interesting and perhaps even more useful if one makes items from them such as back-scratchers, coat or hat hooks, buttons, jewelry, etc. As interesting as modern antlers are, 3 ancient European species during the Pleistocene had antler spreads of about 12 feet.

Antlers grow from and are shed from the pedicles. These are the bony projections on the frontal bones of the skull. Development of primordial cartilaginous pedicles begins early in fetal life due to a short increase in testosterone. These are reported to be detectable on the fresh skull of newly born males. The permanent pedicles develop 3 to 5 months after birth due to another short increase in testosterone and are easily seen.

The growing antler is covered by the velvet and has a number of zones. If one sections the antler lengthwise: under the velvet is very soft tissue referred to as the “undifferentiated zone”, then the cartilaginous zone, then the osseous zone where one type of bone is deposited and then removed and replaced by a stronger type of bone as the antler grows longer. Blood supply to the growing antler is initially through the pedicle which is living bone.

Another increase in testosterone induces mineralization of the antler and later, rutting behavior. Antlers require a considerable amount of calcium and phosphorous. The diet cannot provide all that is needed in the short time allowed so minerals are taken from other bones in the body (mainly the ribs) resulting in a degree of osteoporosis. The animal must then replace these minerals via the diet before the next antler cycle. As mineralization continues, blood flow through the pedicle decreases and eventually is blocked. Then blood supply and minerals must be via blood vessels between the velvet and the antler. If one looks at a large, polished antler, the location of the major blood vessels often can be seen as linear depressions on the antler surface. Antlers are seldom completely mineralized. The tips and base of an antler are usually quite solid, but much of the antler may have a well mineralized outer portion with a center containing many small empty spaces. This center area can be very small diameter or quite large.

Shedding of the antler velvet occurs as the males thrash and rub their antlers against brush and small trees just before and during the rut. Initially there is still blood supply to the velvet, so the antlers are bloody until the blood flow stops and most of the blood has dried or been rubbed off. Even then, there is often some staining of the antler.

After the rut, a drop in testosterone results in demineralization of the antler at the pedicle. As stated earlier, the pedicle is live bone and therefore minerals can be removed. The antlers can then be shed. This whole process can be delayed if females emitting ovulating pheromones are present. If an antler is not shed, a new antler will grow around it the following year. As a side note: removal and replacement of minerals in skeletal bone is a constant process and does not necessarily result in osteoporosis.

There is (or at least used to be) a common misconception that one can tell a deer’s age by the number of antler points. I have examined many yearling (1 ½ year old) deer from Cook and Lake County; the number of antler points ranged from 1 to 4 on a side (or a combination thereof when considering both antlers) and one which had 5 on one side and 4 on the other. However, age does have some bearing on antlers. Studies on moose in Ontario and elk in New Mexico found that antler size increased with age but declined as bulls became over mature. These studies concluded the best trophies for moose were as ages 5 ½ to 11 ½ for moose and ages 7 ½ to 10 ½ for elk.

Another important aspect regarding age is that of their design being either offensive or defensive weapons. Spike antlers are clearly offensive as they can easily injure an opponent. Even slightly larger antlers can cause injuries as their points usually point straight forward rather than curving toward the face and giving it some protection from an opponent’s antlers, such as those of mature males. This shielding of the face is a defensive measure. As an animal becomes over mature, it is common for the number of points (especially those protecting the face) to become fewer and again point straight forward as offensive weapons. I once examined an adult moose that had no frontal points or palms at all, just the main palms that provided no protection of the face. The head of this moose had numerous open and infected wounds.

Two other factors which could be important in some situations are nutrition and genetics. In captive herds where diet is controlled and selective breeding is practiced, there can be measurable differences. However, in wild populations habitat improvement and preventing overpopulation (which reduces habitat quality) may not make enough of a difference in nutrition to be noticed in the antlers except possibly in very extreme situations. Antler genetics of a population can be degraded by very intensive hunting pressure on large antlered individuals for many years; especially if this is compounded by protection of those with very small antlers for their age. Studies have found that deer with good antler genetics will have at least 6 total antler points at 1 ½ years of age. Protecting spike antlered deer protects those with poor antler genetics.

I feel this summary covers the most important aspects of antler development without being unnecessarily long or detailed. The next column will be on regulation of the antler cycle.