And in this corner, wearing the green kaki shorts, hailing all the way from New York State is the current heavyweight champion, 64 years young! And the absolute best way to tell when the whitetail rut occurred with the devastating right hook of science, and a lethal jab, developed in game management classes in southern colleges in the last few years or so. That’s right, born right here in New York state…Fetal backdating.
And in the other corner we have the challenger. Wait, where is the challenger? Oh there he is…rising up over the bleachers like the Great Pumpkin, coming all the way from Europe, at least a couple thousand years old. His beard is deceptive, his age is unknown, the mysterious…Moon theory.
Pardon the foolishness about such a serious subject as determining when the whitetail rut occurs.
But which one is correct? Which one wins the fight? They both have their advocates and detractors, authors and dissenters, and both point to their success with their predictions and appeals to logic and common sense.
Let’s take a deeper look at “the current champion” – fetal measurement, but first a bit of history.
Just after World War II, actually in 1946, a pair of biologists working for the New York State Department of Conservation, came up with a way of determining when the rut or breeding time of whitetails was in prior fall by creating a fetal measurement scale.
This was an expensive and difficult enterprise on a couple levels because it required that a doe, that has a known conception date, be sacrificed for science. The doe is killed on a certain date, the fetus taken out and measured. If two fetuses were in the doe, their length was averaged. And the big question is/was…the sample size large enough? How many does is enough does, killed with known conception dates to create a statistically relevant scale? More on that issue later.
The gestation period of a deer is about 200 days. Glenn H. Morton and E. L. Cheatum used a sample of 17-measured fetus to construct their size/age chart. That’s it. That’s all. Imagine how many fetuses fell in between those 17. And the growth curve of a fetus is not constant, regular, even within the same range and geography; determined by health of the doe, weather conditions, and size variations. (Deer are not all the same size any more than people are.)
Other biologists have their own fetal measurement/age study, including Hamilton, Tobin, and Moore with a southern strain of whitetail, C. Short in Michigan, and R.A. Armstrong, also in New York.
And there is a fairly decent correlation in the measurements of the fetus. At 100 mm, or about two months along in the doe, Cheatum and Morton say the fetus was conceived 54 days prior. Armstrong says the same 100 mm. fetus is 67 days old (a difference of 13 days,) Short’s study in Michigan says it is 79 days along, and Hamilton is pretty close to Armstrong with this one, saying it was fertilized 69 days prior.
So with such a variance, the champ takes one on the chin. Look at the difference between Cheatum and Short! Over three weeks difference in a two-month old fetus. Not even close.
That’s one issue. We are looking for a prediction model that can get us to around a week or so of the rut, right? If it’s off by up to three weeks, it doesn’t do us much good, does it?
By the way, the sample size for the other three studies: Hamilton in 1985 opened up 64 does with known conception dates, Armstrong, 76, and Short, 21.
Measuring a 100 mm fetus can be a problematical undertaking when checking for what they call crown-to-rump measurements because the fetus are sometimes scrunched up and sometimes stretched out. The techs that measure them can vary in their technique a bit (sometimes under physically trying situations) and therefore skew the results (human error.)
So it doesn’t matter if a current study measures hundreds or even thousands of fetuses. They are all put up against the same scale (or scales) determined by a questionable sample size, which has a poor correlation in agreement with other parallel studies.
So how is the moon theory doing with all this talk of fetal measurement? He’s OK. He’s just beaming away.
Study after study has concluded that down through the years, if you average all the fetal…but wait. How can we disprove the Moon theory, that is: that short-day breeders such as whitetails, sheep, and other creatures such as turtles, grunions and smallmouth bass all have internal clock genes timed by photoperiodic (shortening day length) but fine-tuned by the brightness and alternate darkness of the moon?
As the theory goes, light affects some critters more than others by striking the heart of the pineal gland called the suprachiasmatic nucleus and releases melatonin. (Even affects humans.) And melatonin has a depressing effect on certain breeding hormones in whitetails and other short-day breeders like sheep. It is only during the dark of the moon, when the melatonin wears off that the does cycle and we notice the rut is on.
It is common for sheep breeders to use melatonin-soaked sponges, inserted in an ewe to hold back estrus so that when the sponge is removed, all the ewes in the herd will cycle at the same time, after a few days. Handy little thing if you are a lamb breeder.
A lot of people discredit any theory that has anything to do with the moon because of all the spooky (Halloween,) mushrooms, monsters and other myths associated with the moon. And there are lots of reasons for that, one being because it’s fun! It’s fun to be scared.
The moon is just a big rock that reflects sunlight that slightly skews the effect of photoperiodism, that’s about it.
Usually, winners of fights are not determined by a show of hands, and all I can say is, “Look, you should see the other guy.”