27 March 2014

Duiker Data

One of the most common species at Koeberg Nature Reserve is the aptly named Common Duiker.

Common Duiker (Gewone Duiker - Sylvicapra grimmia) giving the camera a smile

One might be expected to get "bored" of loads of common species on your camera traps, but not me. In fact, for me it is exactly the opposite. Each new Duiker photograph is exciting. Why? Because it increases my sample size. You see, the nice thing about common animals are that, well, they are common. As a result they give you lots of data and large sample sizes to play around with. This makes it much easier to see trends in their behaviour.

The most obvious way in which camera traps can shed light on animal behaviour is by recording the animal performing the action in front of the camera. In other words a direct observation.

Common Duiker using its preorbital gland to scent mark

One of the first photographs I got of Duiker at Koeberg was of this individual scent marking a twig using it's preorbital gland. The preorbital gland is a slit of smooth skin in front of the eyes that have glands inside that secrete a tarry substance. You can see the Duiker applying it to one of the twigs in the animated GIF above.

Another obvious way in which camera traps records behaviour is via evidence that some event took place in the past. In other words an indirect observation.

Slightly injured Duiker photographed at Koeberg Nature Reserve

This individual has a strange injury on it's hind leg. My guess would be that it was injured while fighting with another male.

Photographs of direct and indirect animal behaviour are great, but it only gets you so far. What really gets me excited is when I start putting all the "nothing-out-of-the-ordinary" observations together and new trends start to emerge!

I like the spiffy pair of ears on this young male

A few days ago I started capturing all my camera trap data from Koeberg. Some of you might know that I use WildLog to keep track of my camera trapping exploits. The reporting features in WildLog are in need of some love, but I'm still happy that there are at least some features already available. (I'm planning a big overhaul of the reporting features in the "near" future.)

I wrapped up the new version of WildLog (now v4.1) last week and it's now available over here. (Some of you might also have notice that I'm slowly but surely restructuring and improving this blog and the MyWild site. It's a work in progress, but I hope it will be better organised afterwards.)

After importing new data I like to poke around a bit in WildLog and look at some maps and reports. It was during one of these exploratory sessions that I noticed the time of day report of the Duiker.

The observations below are, more or less, ordered by date, with the oldest ones on the left and the newest ones on the right. I started camera trapping at Koeberg during the spring, and this data stretches towards the beginning of March which is heading towards the end of summer over here in the Southern hemisphere.

The current report from WildLog shows the time of day for each Duiker observation at Koeberg

OK, so by now some of you might be thinking: "What's this guy on about? Those are just some randomly coloured lines...".
To which I'll respond: "True, those lines are indeed coloured, but they don't appear to be random at all."

Now I'll be the first to admit that the way I captured and interpret this data is far from "scientific" and not fit for any peer review journal by a mile, but when I notice trends like this in "informal data" I just can't help but wonder whether there might be some reasonably solid biological mechanism behind it all.

Most field guides and books I checked indicate that Duiker are mostly active during dawn and dusk, preferring dusk over dawn. That's all good and well, and looking at my modest sample size I can see that there are indeed many purple (dusk) lines, in fact double the amount of dusk observations compared to dawn. However there are many more day and night observations, but that isn't what caught my eye.

They also say that Duiker will become more nocturnal in areas close to human danger and more active during the day when undisturbed. But, I think it is safe to assume that the Duiker at Koeberg haven't experienced any meaningful change in human activity in the past couple of years. With the majority of observations at the nature reserve during the day it would appear that these Duiker aren't troubled by humans.

What I find interesting is that there seems to be a gradual shift from being almost exclusively active during the day to being active mostly at night. I decided to export the data to CSV (to open it in a spread-sheet application) and try plotting the data using an area chart.

To be honest, I'm very pleased with the result. It really seems to confirm my hunch. The chart below shows the percentage of day vs. night visits over time. Notice how the percentage of dawn and dusk sightings stay more or less constant, but the day and night percentages gradually change over time.
Duiker observations by time of day over time, based on camera trap data

It would appear that the Duiker are more active during the day in the cooler months of spring when the Western Cape still gets lots of cold and wet days. They then gradually shift towards more nocturnal activity as the days warm up. By the end of the dataset the Western Cape is at its hottest and then we also notice the most nocturnal activity.

So from my small sample size I'd venture a guess that the Duiker at Koeberg are adjusting their activity pattern in accordance with the seasons. It will be very interesting to see whether this trend continues and then reverses as we get closer to winter.

Duiker in some typical vegetation for this area

The Duiker activity pattern might sound "obvious" but many species at Koeberg do not show any noticeable difference in behaviour. For example Porcupines are always very strict about being nocturnal, regardless of the season, and the Caracal and Steenbok both tend to lean towards diurnal activity throughout the entire period.

This is what I like about WildLog, it does not try to be a super scientific tool, but it does provide some fancy tools for amateur nature enthusiasts, to help them sink their teeth into animal behaviour and come up with some crazy theories of their own. This is exactly what I had in mind when I started developing WildLog.

I'm looking forward to improving the reports in WildLog. That area chart looks like a winner and I'll definitely add something similar in the next version of WildLog.

Only male Duiker have horns, this one has a broken horn, does it make him less manly?

Another interesting photos, although not really a "good" photo, was this one of a male Duiker with a broken horn. I guess it happened while settling a score with a rival male. Unlike deer, antelope don't grow new horns every year. This broken horn can help to identify this individual in the future, although it isn't 100% accurate because there is a chance that another individual might get a similar injury.

The flies on his back must be extremely annoying and probably a bit of a health hazard. I hope that most are of the normal "house fly" variety and not all related to this monster below.

A type of Horse Fly (maybe Philoliche zonata) commonly encountered at Koeberg

These flies are huge and very persistent. For some reason they feel very attracted to my trousers... I found them intriguing at first. They are large, about the size of the front segment of my little finger.

There are many pollinating flies in the Fynbos biome and initially I thought that this was one of them. I assumed that the straight "mouth" was only used for drinking nectar and pollinating flowers... Boy was I wrong! I found it out the hard way when one of these monsters drilled that needle into my arm! I think I was lucky at first because they had a hard time penetrating the fabric, but when they land on exposed skin they dig in!

These large flies are rather common at the reserve and must be a real pest for any poor animal that crosses it's path.

From what information I could gather both sexes feed on nectar, but the "females are also voracious blood-suckers, attacking a range of vertebrates from frogs to mammals". They can spread disease, so it's best to avoid the nasty bite as much as possible.

I'll wrap up with a much smaller fly that has a more vegetarian nature, ergm, make that the adult has a more vegetarian nature. The larva of these flies pray on the eggs and larva of other insects.

A type of Bee Fly (maybe some Systoechus sp.)


  1. Henry, your observations on the duikers are quite fascinating. the two locations i am trapping at the moment still don't have enough data to do a similar one, but i certainly will look at your trend for the freestate and joburg sites I am doing at present.

    I will keep an eye open for the report updates, as i use your reports at present to give feedback to SANBI at Walter Sisulu Botanical Gardens on the captures there. Any chance of doing a PDF export function for the reports?

  2. Hi Roelof, I'm very glad to hear there are people out there using WildLog. I think the new reports will be the perfect opertunaty to also work on PDF exports. Thanks for the great idea. You are always welcome to contact me directly via email if you have any suggestions, feedback or questions.

    I'm very curious what animals you've camera trapped at Walter Sisulu. We used to visit it often when I was young. The last time I was there (few years back for my dad's birthday) I thought it would be a very interesting place for camera traping.

  3. I've had the camera up there for about half a year now mostly around the Sasol Dam area. There are three factors that influence the camera. One is flash flooding in summer, that wont allow me to place the cam along the river, which I will do this winter,then burning in winter makes that I cant place up against the mountain,where the cam has been up now for the past three months during summer. Unfortunately the garden is a bit more strict about me venturing off the public areas and I am only allowed this after gate hours which is restrictive on getting the cam out deep into the mountain.

    So far the most common is Slender Mongoose, Duiker and Jackal. Ive had a number of porcupine, large spotted genet and Marsh Mongoose.

    The absolute highlight was two captures of a serval one night, the first ever recoding of them in the garden.

    I am yet to get the otters (many tracks), Badger or aarvark. There used to be Caracal, but the staff are not sure if they are sill to be found.

  4. WOW!! The news about the Serval is amazing!! Also good to know the Jackal are still around. I read they found a dead Leopard "recently" next to one of the roads in that area as well, so you never know what you might find ;) But a Serval trumps a Leopard in my book.

    Interesting about the lack of Caracal. Down here around Cape Town the Caracal are doing really well and are very common. I sometimes wonder if places with lots of Jackal have few Caracal and vice versa... I would love to get some Jackal on my camera traps, but most people I've talked to usually say "there were rumours about one a few year ago, but nothing recently".