This post has been a long time coming. Almost a year after wrapping up camera trapping at Tygerberg I finished capturing all of the data and put together some (hopefully) interesting stats. I decided to go without any pretty photographs, and to use only boring graphs, so lets get started. :)
Warning/Disclaimer: My camera trapping at Tygerberg was not part of any official research project. It is a hobby and my main purpose was to try and capture as many species of mammal as possible and confirm their presence.
For those of you that might not know Tygerberg: It a small nature reserve situated in Cape Town, in the Western Cape province of South Africa. It is surrounded by residential areas to the East, South and West. The North opens up to some farmland and quarries. Although the reserve is very small I believe everybody involved was surprised with the diversity of mammals still scraping together a living, surrounded by a major city. I also feel that my involvement at Tygerberg (although not scientific in nature) serves as a great example of what can be achieved in such a small and "boring" area.
A total of 63 creatures where photographed by the camera traps with an additional 5 species recorded by myself while I was setting/checking the cameras. Of these 22 were mammals (all captured by the cameras), 4 were reptiles (of which only Leopard Tortoise and a co-incidental Marsh Terrapin where captured by the cameras), 41 were birds (all captured by the cameras, except for 2 birds of prey) and 1 amphibian was encountered while checking the cameras. Below is the full list of species, showing the number of sightings recorded.
I've updated the info on the MyWild site. It showcases the best 3 photographs for each mammal, together with a map showing the locations of the sightings. You can check it out
over here.
The species accumulation curve was as can be expected: A sharp increase in new species followed by a steady decline and then only occasional increases as I started to target special habitats/species.
I compiled some additional statistics for the mammals. Below are two graphs indicating the average and maximum number of individuals per sighting respectively.
I tend to group photographs together based on "logical" visits. For instance if I get an evenly spaces set of 50 photographs of Bontebok over a 10 minute period I'll record it as one sighting. On the other hand, if two sets of photographs show, for example, a 25 minute gap in between then I'll record two sightings.
An interesting statistic is the maximum number of sightings of an animal in one day. From the chart below one can clearly see what species tend to "hog the camera". Bontebok, Rock Dassie and Vlei Rat can hang around in an area for a long time and continuously pass the camera in frequent intervals.
Other species like the Large-Spotted Genet tend to only pass by the cameras once per day/night. The Large-Spotted Genet's value (of 2) in the graph below is actually the same animal passing two different cameras (close to each other) within a short period of time. In fact of the 11 sightings of Large-Spotted Genet at Tygerberg none returned to a camera during the same night. This is true for this species from other locations as well, with the only exceptions being heavily baited locations where it would sometimes return, but usually only much later.
The next chart indicates the chance of a subsequent sighting of the same species, happening on the same day (given that at least one sighting already took place during that day).
What's interesting about this chart is that it shows some clear differences in the movement patterns of different species. For instance from the data it would appear that the camera is almost twice more likely to get repeat photographs of Porcupine during the same day as from a Small Grey Mongoose.
Another interesting thing I was curious about was the influence of the sun and moon on the animals' behaviour. (I should thank Camera Trap Codger here for some pointers, it was much appreciated.)
There have been lots of opinions about this topic, some more scientific than others. But since this isn't a peer review research paper I'll go ahead and open it up for speculation. :)
Below are some species with interesting results. Whether it accurately reflects the specie's true behavior or sampling bias is unsure.
Overall 58% of all sightings were during the darker (0-50) phase of the moon and 42% during the brighter (50-100) phase.
First up is our friend the Porcupine. These guys are serious lovers of the dark! They adhere to a very strict routine and of the 136 sightings only 4 were well before sunrise or after sunset. The rest were during the (propper) night.
These guys are so strict about only being active when it is dark that they even favour periods of activity at night when the moon isn't shining. They show a clear preference for the darker phase of the moon.
Next up is a lover of the light, and this might surprise some of you, but it is the Caracal. I was surprised to see just how active they are during the day. I guess this can be partially attributed to the diurnal behavior of the Four-Striped Grass Mouse which forms a large part of their diet, but this is still an interesting find.
They don't seem to have a huge preference for what phase of the moon their active in, but they seem to prefer to walk around during the day when the moon is in the 0-50 phase and there are more sightings of them being active during the 50-100 phase while the moon is shining.
The Bontebok on the other hand seem to be less concerned about the phase of the moon and more about whether the sun is shining or not.
The Marsh Mongoose is another night lover that seems to prefer hunting in the darkness. Maybe it relies on its sensitive hands to feel for prey in the shallows?
Is the Small Grey Mongoose's love for being active during the heat of the day linked to it's peculiar relationship with the moon?
This isn't the largest sample size, but the Cape Grysbok seemed much more active during the fuller phase of the moon.
If you're still reading this, thanks, and I hope you found it as interesting as I did to sometimes take a look at the stats behind the pictures. I think small nature reserves such as Tygerberg can provide lots to learn and many wonderful surprises.
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