26 October 2016

Koeberg Data Summary - The Patterns

One of the benefits to using camera traps to monitor wildlife is that it can be active for 24 hours per day, day in and day out. This makes it possible to start examining the day-night cycles and even moon phase activity patterns of animals. Below are some of the theories I came up with. (As always please take all of these "statistics" with the appropriate grain of salt.)

The "dune cliff" at Koeberg Nature Reserve

One of my favorite things to compare between species is the difference in their day-night activity patterns.

The closer you get to the poles, the greater is the seasonal difference between sunrise and sunset times. As a result when working with more than a year of camera trapping data you can't simply compare the observations based on the time alone. Instead you have to compensate for the difference in the length of the day.

I like to group the observations into categories, for example sunrise, early morning, mid day, etc. The general distribution still looks the same, but in this way I can more reliably compare observations over a longer period of time.

The Eland (Eland - Tragelaphus oryx), Common Duiker (Duiker - Sylvicapra grimmia) and Steenbok (Steenbok - Raphicerus campestris) all showed more or less the same activity pattern. Showing peaks of activity during early morning and late afternoon as well as an increase in activity around midnight. But there are small differences between the species, for example the Duiker seem much more active at night and the Steenbok seem to be more active at mid day. The Eland was also the only one to be more active in the late afternoon compared to the early morning.

However, the Springbok (Springbok - Antidorcas marsupialis) showed a different pattern compared to the other herbivores mentioned above. It lacked the spikes in activity around late afternoon and at mid night. Why this is I'm not sure. Maybe during the later part of the day the herd moved out of the areas where the cameras were placed, or maybe it is a reflection of seasonal changes in behavior. Most of my camera trapping in the area where the Springbok hang out happened in the autumn months.

The above species all showed both diurnal and nocturnal activity, but some species are very strict about their preference. As alwys the Porcupine (Ysterverk - Hystrix africaeaustralis) at Koeberg are strictly nocturnal.

The Porcupine even seem to go as far as to avoid the moon. The number of observations are heavily skewed towards times when the moon is not shining. This trend at Koeberg is consistent with my observations at Tygerberg were the Porcupine showed an almost identical pattern, being highly active during new moon and less active during full moon. Both locations also show far more observations during periods the no moon visible, but this latter effect is less pronounced in the Koeberg data compared to Tygerberg. My guess would be that because Koeberg is more remote and has less human activity at night, compared to Tygerberg, the animals are a little more comfortable to go about their nightly routine.

The polar opposite of the Porcupine must be the Small Grey Mongoose (Kleingrysmuishond - Herpestes pulverulentus) which is only active during the day.

The Small Grey Mongoose and Caracal (Rooikat - Caracal caracal) both prey on rodents, but it seems fairly safe to assume that they prey on different species, for the most part. The chart below is fairly busy, but I wanted to show how the activity periods of the predators at Koeberg overlap with their prey. The two Gerbil species are mostly exposed to predation from Caracal and Small-Spotted Genet (Kleinkolmuskeljaatkat - Genetta genetta), while the Four-Striped Grass Mouse (Streepmuis - Rhabdomys pumilio) primarily has to deal with the Small Grey Mongoose and a small amount of pressure in the late afternoon from the Caracal.

By far the majority of observations were of single animals, but there are some interesting exceptions. Porcupine families tend to travel together fairly regularly and as a result they have a much larger percentage of observations with two or more individuals.

For some species it is also possible to differentiate between the sexes. For both Steenbok and Duiker the males seem to get photographed more frequently. Maybe they patrol their territories more actively, or walk around more while looking for females? Interestingly the male-female sex ratio seems to be even more exaggerated for Duiker compared to the Steenbok.

The last theory I want to touch upon is one that originated from way back in March 2014 when I did a blog post about it, over here. I had a theory that the Duiker at Koeberg seem to adjust their activity pattern based on the season. The data seems to support the idea, showing that the Duiker are very active late at night during the warm summer months and much more active early in the morning during the cool winter months.

This past couple of posts analyzing the camera trap data from Koeberg is just the tip of the iceberg. I'm sure there are many more discoveries to be made in the future, but in the next couple of posts it is time to share some more camera trap photos and a new nature reserve.

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