Camera traps offer a peek into the minds of nervous deer
Last summer I was going fishing as part of an inland fisheries class with North Carolina State University’s (NCSU) Wildlife Summer Camp. While I was walking around the pond to secure a section of the bank to fish, I stumbled upon a baby white-tailed deer, which was curled into a ball near the pond bank. It didn’t move or make a sound. In fact, I reached down and scooped it into my arms before my teacher, a deer researcher at NCSU, and classmates caught up to me. Because we were part of a class, we had appropriate permits to handle wildlife (don’t try this at home). We learned how to age the fawn based on size and behavior and determined it was only seven days old! The fawn was not stressed, so we took pictures, before releasing it back where it was hiding. We loved the experience of seeing a wild deer fawn up close, but why hadn’t the little guy run away as we approached?
Deer fawns are covered in hundreds of white spots (300 on average) that help to camouflage them. For the first one to two weeks of life, white-tailed deer rely on this camouflaging pattern to protect them from predators. Rather than fleeing at a sign of danger, fawns stay motionless to avoid detection. Mothers commonly leave their fawns for hours at a time, before returning to let the fawn nurse. The following photos show how well fawns are camouflaged (note that the young were radio-collared as part of a research project).
During the second week of life, young deer are steadier on their feet and will flee rather than sit still when threatened. By the fourth month of life, the protective white spots that once covered their fur start to disappear. Predators remain a threat to deer and after losing their camouflaging spots, these young deer must find new ways to avoid predation. Mainly, they adjust by being on the lookout for predators, and then running away as fast as they can if they sense danger. When deer are looking for predators, they are exhibiting what we call vigilance behavior: they hold their heads high, often with perked ears, looking and listening for potential threats. However, vigilance comes at a cost; there is a trade-off between having your head up to keep an eye out for predators and having it down near the ground to browse for food. Thus, vigilance behavior can directly influence the health of each individual deer because it takes away from the amount of time they can spend foraging. Of course, vigilance is worth it because it helps keep them alive if deer-eating predators are stalking nearby.
Scientists are increasingly interested in measures of deer vigilance because it provides a window into how deer see the world – a direct way to measure how nervous a deer is. With a metric like this, we can start to ask questions about what types of things make a deer more or less nervous, and therefore, more or less able to browse the local vegetation. Camera traps and direct observations are ways researchers can watch this behavior and several new studies report factors that influence deer vigilance.
In one study on deer vigilance in North Carolina, researchers baited 100 motion sensitive camera traps and used the pictures to determine how often the animals had their heads up looking for predators, or down munching the corn bait. After coding the behavior of 40,000 deer photos they discovered that deer increased their feeding time (i.e. were less nervous) as their social group size increased. Their results make sense; more eyes in the group allowed individuals more time for feeding, rather than looking for predators. They also determined that males were less vigilant than females, meaning they spent more time foraging. The researchers hypothesized this behavior was due to males’ larger body size, which might make them less likely to be attacked by a predator (primarily coyotes at this site).
Another project with elk in Montana found that all-male herds were less vigilant than herds with females, and that a higher calf-to-cow ratio resulted in a more vigilant herd. The North Carolina deer study also found this result: when fawns were present, females were more vigilant than when no fawns were present.
The North Carolina study also evaluated vigilance compared to time of day and moon phase. Deer were less vigilant in the afternoon and during brighter moon phases, likely because they were better able to see approaching predators.
Meanwhile, another group of researchers in Poland determined that olfactory cues, like fresh wolf scat, also affect vigilance in red deer. Red deer doubled their vigilance behavior when wolf scat was present, suggesting that predators’ scent alone can put deer on high alert. When deer smell that predators may be nearby, they are much less likely to forage, but rather spend their time looking for those predators.
Together, these studies show that camera traps can be great tools for studying the factors that affect deer predation risk. They have confirmed the importance of group size in protecting against predators, and suggest that prey also adjust their defenses daily based on light levels, and locally if they smell a predator. However, I think we are just starting to scratch the surface at what else we can learn about predator-prey systems with this new vigilance measure, and I’m happy to be helping with a new study that extends this past work by analyzing deer across 32 parks in the eastern United States.
eMammal is a citizen science research project that enlists local volunteers to run camera traps and then share the pictures with scientists. At the Biodiversity Lab of the North Carolina Museum of Natural Sciences, we are now going through these pictures and quantifying how nervous each deer is, how often they have their head down to feed, or up to look around. This data set is stratified across areas of different human use, so we will be able to evaluate the effect of people, as well as coyotes, on deer behavior. Some of our cameras are in hunted parks, while others are in unhunted lands. Some are on busy hiking trails, remote hiking trails, or off in the middle of the woods, allowing us to also check to see if human foot-traffic is important to deer. Finally, we also get counts of coyotes on these cameras, so we will factor them into the analysis as well.
I often come across fawns in the pictures we are using for this study and laugh as they play or chase insects in front of the cameras, always thinking back to the fawn I found last summer. Although we don’t have any conclusions yet from these images, we will soon be able to add up all of our data and plot results – I can’t wait for that eureka moment. Whatever we discover, I will present a poster on this research at The Wildlife Society meeting in October.
Follow me on Twitter @sumdawg to see the best pictures from the research!