Penn State Deer-Forest Study

Almost 10 years ago we wrote a blog post about temperature and buck movements during the rut. If you enjoy spoilers, you can read it.

But it also has been a decade and we have a lot more locations on buck movements (97,979 to be exact). So maybe we can observe something new from our data?

Let’s start by laying some facts on the table.

This is what temperature has done during the rut from 2013–2023. The blue line is the trendline, blue dots are the daily average, which indicate from October 1 to December 1 the average temperature drops, on average, half a degree every day. But on any given day the maximum temperature could differ by as much as 20 degrees. The daily minimum temperature does the same thing except it averages about 20 degrees cooler.

Over 2013–2023, in the graph below are the average buck movements during the day (yellow) and during the night (black). The gray area is a measure of the variability about the means. You can see that bucks travel about twice as far at night than during the day at the peak of the breeding season.

But you also need to remember that daylength is getting shorter so there are more hours in the dark. So even if bucks traveled at the same speed all 24 hours, they would cover fewer miles during daylight hours. That means NOT ALL of the difference between night and day is because bucks move more at night. If you want to learn more about buck travel speeds during the rut, read this.

Let’s plot the average distance moved during the daytime as a function of daily maximum temperature. Look at that! The warmer it is the fewer miles they travel!

But hold on a minute. When is it warmest? In early October when the rut hasn’t really started (see all those dark blue dots in the lower right corner of the cloud of points? Those are days in early October before the rut has kicked in.)

I don’t think this graph tells us anything about how temperatures affect deer movement.

Let’s try this. If it’s warmer than normal, then the maybe daily movements are less than normal? Let’s plot the following:

On the x axis will be the daily maximum temperature
On the y axis will be the difference in movement compared to the mean distance traveled. For example, if it were November 13^th and the 2013-2023 average distance traveled was 2 miles, and if on November 13, 2020 the average distance that bucks traveled was 1.5 miles, then the y-axis value would be -0.5. That is, in 2023 bucks traveled 0.5 miles less than the 2013-2023 average.
The prediction, based on what I’ve read in the comments section, is that if deer only traveled 1.5 miles on November 13, 2020 then the daily maximum temperature must be warmer than usual.
At warmer temperatures we should see below-average movements (y-axis values less than zero).

Umm… I don’t see any pattern. And statistically there is no relationship between deviations from the average distance moved and daily maximum temperature. The blue dots are movements during peak rut (1 week either side of November 13).

Let’s try it for nighttime but use daily minimum temperature.

Once again, no relationship. And again the blue dots are movements during peak rut (1 week either side of November 13).

Every single year, throughout the rut, we regularly experience deviations in temperature of 10 degrees from average – either warmer than average or cooler than average. Yet the deviations in movements from one year to the next cannot be explained by changes in temperature.

I think our next question should be “Why AREN’T buck movements related to temperature?”

It’s the more important question. I’ll cover that in my next post.

-Duane Diefenbach

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13 comments on “The Heat Is On…”

To your final question of the post, inquiring minds want to know!

Duane, your stated hypothesis is “deviations in temperature …… either warmer than average or cooler than average” will affect movement, but the independent variable in your analysis is mean daily temperature. It would be interesting to calculate the deviation from the mean temperature, just as you did for movement, and use that as the independent variable in a test of the hypothesis.

I think blue and black are reversed in the males-nighttime graph.

Duane Diefenbach says:

January 7, 2025 at 1:49 pm

The independent variable was the daily max or min temperature. For each year, we had deviation of movement from the mean (for that day) and that day’s maximum (or minimum) temperature

That is a lot of detailed data for the average person to digest. GOing to have to get my son to tell me what I am looking at.

It would be interesting to know how temperature affected hunter movement. bs

I’d be interested in seeing data on the distance traveled as a function of the difference from the average temperature for that date. AND data on the distance traveled as a function of the difference in temperature from the preceding several days. In other words, how much do they move if temps are different than average, and how much do they move if there has been a change in daily temperature (cold front, etc). For example, if it has been a high of 65F for three days and then on the fourth day the high is 45F, what happens to the movement?

DT says:

January 7, 2025 at 11:24 am

100%. And also, how do other weather patterns that often influence fronts (i.e. rain storms) impact movement.

I’ve seen multiple studies from PSU, MSU and others that basically state the same thing: Temperature doesn’t impact movement to any discernible degree. It’s as rudimentary as science can be (perhaps not even scientific at all :)), but I have a spreadsheet that tracks buck sightings across 6 cameras for four seasons and every major cold snap saw a rise in bucks captured on camera.
Andy Turner says:

January 9, 2025 at 11:59 am

Agree.

What does the data show for the winter months? Are they bedded down somewhere? Do they move to eat? How far? It’s been pretty cold in Central PA these last few weeks. Just wondering what they do to survive the winter. Thanks.

Unrelated to this post I have trail camera pictures this January 6th of a ten and eight point locking horns for five minutes while another eight point thrashes around a small tree. Surprises to see this activity in 15 degree temps and 6 inches of snow on the ground.

My experience while deer hunting is that cold temps inspire hunters to move more. Perhaps to warm up. Moving hunters move deer and so that is why it seems like deer move more during a bitter cold day.

Thanks for digging into this for us. “And statistically there is no relationship between deviations from the average distance moved and daily maximum temperature” –Across the entire temperature range, this looks true, but if you look at the highest daily temperature maximums (65F and up) during peak rut, there are a lot more negative distances in mean distances travelled (blue dots below the line).

Once again great information using actual data collected over the years that prove or disprove theories about deer movements. My observations while hunting or just spending time outdoors is that outside of being pushed by humans or other predators, whitetail deer move mostly for food or sex. I know….it’s much more complicated that, depending on the time of year, but just trying to keep it simple.

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