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Blown Away

Posted: March 26, 2018

Find out what deer have to say about those Rainy and Breezy October days!
(click for larger image)

(click for larger image)

Wind and rain can be annoying, and some might call it distracting or disruptive, especially while hunting. 

But wind isn’t all bad. It can be quite refreshing. Think about when that perfect breeze blows through just in time to cool you off on that hot summer day. You can’t beat that! Rain on the other hand… is necessary but to be honest, it’s not my favorite product of nature.

What do deer have to say about those rainy and breezy days in the forest?

In a 2015 post, Leah Giralico wrote about the unexpected way wind was affecting deer movements. Instead of slowing them down, it was increasing their movements during the day. 

This seemed counterintuitive to nearly everyone. In a reader survey about white-tailed deer movement, almost 90% thought that wind would cause deer to reduce their movements! About 53% believed rain reduced deer movement and 11% felt that rain would increase deer movement.

Graph1

Readers were asked what level of wind would cause an effect on deer movement given the following choices:

  • Light breeze (wind felt on face, leaves rustle)
  • Gentle breeze (leaves and small twigs constantly moving)
  • Moderate breeze (dust, leaves, small tree branches move)
  • Fresh breeze (small trees begin to sway)
  • Strong breeze (larger tree branches moving, whistling in wires)
  • Near gale (whole trees moving, resistance felt walking against wind)

Over half of readers agreed that a significantly windy day would affect deer movements. 

 

Graph2

Leah analyzed data from October 2013 and discovered that male and female deer were moving more during windy days and less during windy nights. Even slight air movement made a difference in deer activity. With regard to precipitation, she found that females were not affected but males traveled significantly less on rainy days.

If we know this already, why are we asking the same wind and rain question again? Because science likes replication. Will we get consistent results from year to year? Let’s see.

Given the fact that wind speeds barely reached 12 mph in October of 2013, it wasn’t a very windy month. This could have influenced the results. If there are more windy days in October of 2015 and 2016, would the same effect on movement be detected? What about an interaction between wind and rain? Wind and rain together might cause a different response in deer movement than just wind or just rain.

To find out we conducted the same analysis that was used in 2013.  

We separated wind speed levels into these three categories:

  • Calm: Winds less than 1 mph;
  • Gentle/Moderate Breeze: Winds between 1 and 15 mph;
  • Strong Breeze: Winds between 16 and 27 mph

Rain was categorized as either

  • Rain
  • No Rain

We calculated the miles deer traveled during 3 time periods: day, night and crepuscular periods (dusk and dawn). We collected weather data from Weather Underground and analyzed male and female movements at each of these wind levels for each periods. We then did the same for rain.

The analysis says… 

Wind and rain had a greater effect on males than females! 

Also, instead of finding that wind affected day and night movements differently as they did in 2013, we found that the effect of was the same for both!

Bucks increased their movements when a gentle wind was blowing, but only if it was not raining. A strong wind caused buck activity to increase significantly whether or not it was raining but had no effect on does. 

Graph4 

Similar to 2013, bucks were moving less during windy nights.

What about the rain? Well, in 2013, Leah found that rain decreased buck activity. This was only the case in 2015 and 2016 if there was little to no wind. 

This shows that there is an interaction between strong wind and rain. Deer respond differently when there is wind and rain together rather than just wind or just rain. Rain alone causes a decrease in buck movement. But a little rain has no effect on buck activity if there is a strong wind blowing. Strong winds will increase buck movement no matter what!

Females have a little bit different strategy for dealing with wind and rain. The plot shows that at night and during the day a light breeze causes a slight but not significant increase in movement. But at higher wind speeds, activity drops back down to normal. Likewise, rain had no significant effect on female movements whether it was windy or not. 

Graph3

As noted, winds speeds did not get above 12 mph in 2013, but those results suggested increased movement with increased wind speed. However, 12 mph winds are only moderate, so the effect of strong winds could not be tested. 

October 2015 and 2016 were much windier months (the highest recorded winds were 10 to 15 mph faster) so we could examine how deer reacted to stronger winds. 

Once wind speeds reached 16 mph, doe movements were no longer affected. Females showed a biologically insignificant increase in their movements at lower wind speeds (1 to 15 mph) but neither increased or decreased their movements at higher wind speeds (16 to 27 mph). 

Most of our readers also thought that wind would only affect deer movement if it was a strong wind and many thought that wind would cause deer to decrease their movements. 

Not only did bucks increase their movement on windy days, but it only takes a light air movement to cause them to increase their activity. Bucks seem to like stronger winds and move more no matter how strong the breeze or how much it is raining while females don’t really care either way. 

Keep in mind that these results are only observational. We cannot control the weather. But it appears that wind has a greater effect on the activity of males than females at higher wind speeds and that rain and wind influence buck movements even more when they are in combination with each other.

Wind does influence deer movement but not in way most people would expect.

The take-home lesson? Now you have no excuse for changing hunting plans on those windy or rainy days!

-Jessica Hepner
Undergraduate, Wildlife and Fisheries Science

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