A down-time habit of mine (my wife might argue it’s an obsession) is to watch auto repair videos on YouTube. I especially enjoy the challenges auto repair techs face when dealing with electrical problems.
Here’s what good mechanics (technicians) don’t do. They don’t plug in a scanner and based on the error code start firing a parts cannon at the vehicle to fix it.
Instead, they use the error code as a starting point. Referring to electrical wiring diagrams and their knowledge of vehicle operation, they use logic and deduction to identify the problem.
For example, if the cause of a LCD black screen and no radio is a bad fuse, then we should observe no power to the module based on the prediction that the fuse is the cause. Just Watch Wes Work and you’ll see what I mean. This approach ends up saving money (sometimes a lot!) because a) the technician spends less time diagnosing the problem, b) less money is spent on parts, and c) the root cause of the problem is more likely to be fixed.
By the way, if you’re now intrigued about car repair videos, you can Watch Wes Work (Illinois) or check out Diagnose Dan (Europe), South Main Auto (New York), and Pine Hollow Auto Diagnostics (State College, PA). (If she’s reading this, my wife is rolling her eyes right now!)
It’s similar in science. Unfortunately, we don’t have a wiring diagram to consult but we can observe a phenomenon, develop a hypothesis about what causes that phenomenon to persist in a species, and then test the hypothesis by making predictions and conducting experiments to invalidate our hypothesis.
So where am I going with all this? To the moon.
Years ago, the big rock that orbits the earth entered the realm of popular deer-hunting literature which drew a connection between white-tailed deer breeding behavior (and, ultimately, hunter buck harvest success) and moon phase.
Let’s think about this by first asking why do white-tailed deer breed? The goal of each male and female is to produce offspring that survive, breed, and pass on their genes to future generations.
The first step in reaching this goal is by successfully breeding. The second is doing everything they can to ensure their offspring survive and breed.
Males play no role in gestation or fawn rearing. They can only participate in the first step of the process and this dominates their strategy.
For females, the second step is the most critical. White-tailed deer have a 200-day gestation period, which means the females that become pregnant in mid-November will give birth around June 1st the following year.
What does a female need to maximize her fawn’s survival and ability to reproduce?
- To acquire sufficient resources (food) to give birth to a healthy fawn
- To give birth as early as possible so that the fawn has as much time as possible to grow large enough to survive the following winter. And, if possible, become pregnant and reproduce in that first year. BUT not so early that the newborn is exposed to adverse weather conditions that may reduce its chances of survival.
What consistent, predictable environmental cue might be able to trigger breeding behavior in females so that 200 days in the future she gives birth at a date that matches #2?
I don’t think a National Weather Service bulletin, or the Farmer’s Almanac will help a deer!
Moon phase, with a periodicity of about 30 days, is certainly predictable but does it say anything about weather conditions 200 days in the future? I doubt it.
You know what does – daylength (photopheriod)!
Daylength in November is the same every year, and so if the physiology of white-tailed deer was such that November daylength triggered hormonal changes that induced physiological events like ovulation then we would have a hypothesis about how timing of breeding is controlled in white-tailed deer.
We can then make a prediction to test our hypothesis.
If we put a white-tailed deer in an environment where we can regulate daylength we should be able to induce breeding behavior any time of the year. In fact, this has been shown to be true for any number of ungulate species.
In addition, science can take us even further and make predictions about the hormonal mechanisms that are triggered by changes in daylength. It gets complicated really fast, but by treating deer with the hormones melatonin, progesterone, and gonadotropin, Osborn et al. (2000) were able to induce out-of-season breeding in white-tailed deer. It didn’t work quite as well as controlling daylength, but it worked. They also demonstrated that some males had adequate fertility and libido to impregnate females in midsummer.
There is no ecological or physiological reason why moon phase should affect the timing of breeding in white-tailed deer.
Timing of breeding in Pennsylvania is not related to moon phase. Also, Diefenbach et al. (2009) published a paper that found no evidence of changes in timing of births in Pennsylvania despite changes in the sex-age structure and density of the deer population.
The next time someone tells you how the moon, the weather, or whatever else they come up with, affects the breeding behavior of white-tailed deer, pause for a moment and ask yourself:
How does _____________ improve the chances that a fawn born 200 days later will survive and reproduce?
If you really want to be a smarty pants, ask this oracle of deer breeding how one would go about testing their hypothesis!
Remember what the auto repair techs do, observe a problem, investigate, hypothesize, test. Because if you can’t test the hypothesis, it’s not science…or auto repair!
-Duane Diefenbach