The trouble with shade
Who knew that shade could be so problematic? A couple of weeks ago, I wrote about how shade seems to be my biggest obstacle in reconciling how the cameras see the world vs. what is actually going on. My job is to figure out how to make things right.
To start with, the camera traps are up on trees. Mostly. As you know, the cameras are on a rough grid layout – 225 grid cells, each 5km2 (2.236km on each side) — covering a total of 1,125 km2 of Serengeti’s center. This kind of design makes sure that we are covering enough of the landscape to capture the bigger picture of animal distributions and movements. Each camera is roughly at the center of each grid cell – on the closes suitable tree to that center point. Some trees are big and shady; some are small and spindly. In the woodlands, there are trees everywhere; on the plains, the camera-trap tree can be the only tree for miles. And sometimes there are no trees at all, and here the cameras get put up on metal poles.
These different habitats are important to capture. I think that animals might behave very differently in areas with lots of trees than they do in areas with very few trees. When it comes to the aggressive interactions between carnivores, for example, trees, shrubs, and tall grass provide great hiding places for the smaller species. It’s like trying to hide from someone you don’t like in an empty room vs. in a really huge, crowded shopping mall.
The problem is that camera traps work better in some habitats than others – at least for certain species. Say you are a huge, muscle-bound lion. Even standing is tiring in the Serengeti heat, and you spend your days breathing heavily even at rest. You like shade. A lot. If you are out in the open plains, a single shade tree will stick out for miles, and you’ll probably work your way to it. Chances are, that tree has a camera. In the woodlands, though, there are lots of trees. And the camera trap could be on any one of them. So even if you’re searching for shade, the chances of you walking past the camera trap in the woodland are far smaller – just because there are so many trees to choose from.
Here’s a map of the study area – green shows more densely wooded areas, whereas yellow marks the plains. Camera traps that have captured lions are shown with circles; the bigger the circle, the more lions were seen at that trap. I know for a fact that there are more lions in the northern half of that map than in the southern half, but the lions out on the plains seem to really like getting their picture taken!
The pattern looks a little better at night than in the day, but it’s not perfect. So perhaps shade isn’t the only thing affecting how these cameras “see” lions in different habitats.
As depressing as this problem seems at first glance, I’m optimistic that we can solve it (enter Kibumbu’s new GPS collar!), but those methods are material for another day. In the meanwhile, what else do you think might be going on that attracts lions, or other animals to trees, besides shade?
7 responses to “The trouble with shade”
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- December 16, 2013 -
Trees are good for climbing in too, either to hunt, hide, or rest.
If there is shade, and the species seeks it and is a social species, might the potential of social interaction be an attractant?
Food – leaves, bugs, little critters, etc…
It’s interesting that you seem to have fewer stations capturing images during the night than during the day. Are the number of captures roughly equal, being offset by greater numbers of captures at certain stations (e.g. BO7 / KO4)? Why would you have a comparatively larger number of stations being triggered, albeit with fairly few captures, during the daytime?
Excited to see the lion movement data you’ve collected.
Tor, that’s a *great* question. My best guess at this point would be the attraction of shade during the day means that lions might go out of their way to visit a tree in daylight, but might walk on past it at night.
There do seem to be a lot of reasons why the animals use trees besides shade – certainly for climbing (for leopards and sometimes lions). One thing I didn’t realize until pouring through the photos is that carnivores are using trees not so much for social interactions but for *communication* — specifically, scent marking, as you can see here: http://talk.snapshotserengeti.org/#/subjects/ASG000700t
Cheetahs in particular seem to be really scent-oriented, hence the many close-ups of both ends!