Things are looking up!
I’ve got to echo Margaret’s apology for our sporadic blog posts lately. Things have been a bit hectic for all of us — Dr (!!!) Margaret Kosmala is finishing up her dissertation revisions and moving on to an exciting post-doctoral position at Harvard, our latest addition, Meredith, is finishing up her first semester (finals! ah!), and I’m knee deep in analyses (and snow!).
So,\ please bear with us through the craziness and rest assured that we’ll pick up the blog posts again after the holidays. In the meanwhile, I’ll show you something that got me really excited last week. (Warning: this involves graphs, not cute pictures.)
Last week, I was summarizing some of the Snapshot Serengeti data to present to my committee members. (My committee is the group of faculty members that eventually decide whether my research warrants a PhD, so holding these meetings is always a little nerve-wracking.) As a quick summary, I made this graph of the total number of photographs of the top carnivores. Note that I’m currently only working with data from Seasons 1-3, since we’re having trouble with the timestamps from Seasons 4-6, so the numbers below are about half of what I’ll eventually be able to analyze.
The height of each bar represents the total number of pictures for each species. The color of the bar reflects whether or not a sighting is “unique” or “repeat.” Repeated sightings happen when an animal plops down in front of the camera for a period of time, and we get lots and lots of photos of it. This most likely happens when animals seek out shade to lie in. Notice that lions have wayyyy more repeated sightings percentage-wise than other species. This makes sense — while we do occasionally see cheetahs and hyenas conked out in front of a well-shaded camera, this is a much bigger issue for lions.
I also dived a little deeper into the temporal patterns of activity for each species. The next graph shows the number of unique camera trap captures of each species for every hour of the day. See the huge spike in lion photos from 10am-2pm? It’s weird, right? Lions, like the other carnivores, are mostly nocturnal….so why are there so many photos of them at midday? Well, these photos are almost always lions who have wandered over for a well-shaded naptime snoozing spot. While there are a fair number of cheetahs who seem to do this too, it doesn’t seem to be as big of a deal for hyenas or leopards.
Why is this so exciting? Well, recall how I’ve repeatedly lamented about the way shade biases camera trap captures of lions? Because lions are so drawn to nice, shady trees, we get these camera trap hotspots that don’t match up with our lion radio-collar data. The map below shows lion densities, with highest densities in green, and camera traps in circles. The bigger the circle, the more lions were seen there.
The “lion hotspots” in relatively low density lion areas have been driving me mad all year. These are nice, shady trees that lions are drawn to from up to several kilometers away, and I’ve been struggling to reconcile the lion radio-collar data with the camera trapping data.
What the graphs above suggest, though, is that there likely to be much less bias for hyenas and leopards. Lions are drawn to shade, because they are big and bulky and easily overheated. We see this in the data in the form of many repeated sightings (indicating that lions like to lie down in one spot for hours) and in the “naptime spike” in the timing of camera trap captures that suggest lions seeking out shade trees to go to. Although this remains a bit of an issue for cheetahs, what the graphs above suggest is that using camera traps to understand hyena and leopard activity will be much less biased and much more straightforward — ultimately, much easier than it is for lions. And this is really good news for me.