Deer Crepuscular, Nocturnal, or Diurnal?
Quick answer: Deer are Crepuscular.
It’s a common scene, you are driving home after visiting a relative and the sun is slowly disappearing behind the distant horizon. You are feeling a bit drowsy and may not be paying close attention when BOOM, you hit a deer. The crepuscular deer crushes your front bumper and most likely your evening. Why is it that so many vehicle to deer collisions occur during the twilight hours? It’s because deer are largely crepuscular, which means they are most active in the hours just before the sun goes down in the evenings, and just after the sun crests the horizon in the morning. This sadly occurs at the same time when most people are feeling a bit drowsy and visibility is low.
Terminology:
Before we continue, it may be helpful to go over some terminology. All term definitions are taken from Merriam Webster I will use these definitions later to analyze this animal in particular.
What Is The definition of Crepuscular?
According to websters dictionary, crepuscular refers to either something that is related to or resembling twilight. In the context of animals (the context we care about), it means they are active during the twilight hours. The twilight hours consist of the brief time before sun rise and after sunset when the land is still lit but the sun is not visible.
For practical reasons, the twilight hours are split up into 3 different types:
- Astronomical Twilight
- Nautical Twilight
- Civil Twilight
As you can see, twilight is well defined. You can actually look up the EXACT times for each of these twilight defintions on a site such as timeanddate.com. I recommend you enter in your local time and play around with it.
What Is The Definition of Diurnal?
Diurnal means during the day. Diurnal animals are most active during the day. As such, we humans are considered diurnal
What Is The Definition Of Matutinal?
Back to the rare words! Matutinal means of or occurring in the morning hours. Most matutinal animals may be considered crepuscular.
What Is The Definition of Vespertine?
Vespertine is the opposite of matutinal, as such, it means of or occurring during the evening hours. Most vespertine animals can be considered crepuscular.
What Is The definition of Nocturnal?
Nocturnal is a more common term than crepuscular. It simply means that the animal is most active at night. This word is quite a bit simpler!
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What Time of Day Are Deer Most Active?
Students, hunters, and wild life enthusiasts are all curious as to what time of day deer are most active. As such I will go over some of the possibilities below.
Are Deer Crepuscular?
Personal experience would indicate a resounding yes. But as we know, personal experience, while helpful, does not always provide an objective guide. I managed to wrangle up two papers that suggest yes, deer are crepuscular. To briefly quote one source without surrounding context: “Based on rate of movement, deer had clearly defined crepuscular activity patterns.”
Another source, which has a full article attached to it, studied deer and elk in canada and the netherlands. All herds displayed crepuscular activity, but there is a twist: the deer in canada were shown to be mostly crepuscular + Diurnal, while the deer in the Netherlands were mostly crepuscular + Nocturnal. The paper suggests that the differences were attributed mostly to human disturbances on a daily scale and local weather on an annual scale. As with all things, the devil is in the details. If you are interested in the details, the abstract has a free 11 page pdf attached to it…I certainly wish more academic papers were free!
In short, while there is a lot of variation on whether deer supplement their crepuscular hours with day time activity or night time activity…deer do seem to be mostly crepuscular across the globe.
Are Deer Diurnal?
Most academic papers I have seen, including the ones I have cited already on this page, indicate that some deer may exhibit diurnal activity patterns in addition to their crepuscular activity patterns. It seems this variability is due to a number of factors such as:
- Human Activity
- Weather, both daily and seasonal
- Species
Are Deer Matutinal?
To rehash: a matutinal animal is active in the morning hours. Most crepuscular animals are also matutinal. As such, deer may be considered matutinal.
Are Deer Vespertine?
To rehash: A Vespertine animal is active in the evening hours. Most crepuscular animals are also vespertine. As such, deer may be considered vespertine.
Are Deer Nocturnal?
This question is similar to the diurnal one above. While most deer seem to be crepuscular, there is a great deal of variation on whether a deer is diurnal/nocturnal. It appears that yes, some deer are nocturnal!
Why are deer largely crepuscular? That is a difficult question to answer, as it’s not obvious which evolutionary selective pressures lead to this behavioral instinct to be developed in crepuscular deer. It may have been that at some point in history the lower visibility enabled the deer to escape from predators easier. Sadly for the deer, many of deer’s natural predators such as the mountain lion also evolved to be active during the crepuscular hours. It may also be that the more moderate temperatures of the twilight hours allow the deer to be active in comfortable conditions while avoiding the extreme temperatures in climates that have larger variances in daily temperature. This is particularly relevant for north american deer, as the temperature in many of their habitats can vary wildly.
I should point out, that there is not a hard line between the most active crepuscular hours and the rest of the day. While deer are largely crepuscular, it’s not uncommon to see deer moving around during all hours of the day. There are a number of possible explanations for this.The deer may have spotted a predator, or caught wind of a strange scent in the air. As prey animals, deer are always on the look out for anything strange and out of the ordinary. Sometimes deer are forced to stay put and bed down during the night. In these scenarios they must make up for lost time by foraging during the day. However these anomalies seem more common than they really are, as we generally only see deer when we ourselves are awake. As a general rule deer stick to the crepuscular hours for pragmatic reasons.
If you live in an environment where there are bountiful crepuscular deer populations, it’s important that you take care to avoid deer related accidents. The easiest way to avoid these accidents is to not drive during the crepuscular twilight hours. However, I realize this is wildly impractical in most places. The next best thing is to ensure that you have proper visibility while driving. Make sure your windshields are clean and that your headlights are clean and shining brightly. Use your bright lights when possible to further increase your field of vision.
If you are interested in other crepuscular prey animals or even other topics with the word crepuscular in them, check out the following link:crepuscular rabbits.
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