One of our first goals on Redonda was to get a good sense for the density of lizards on the island. This is one of the key metrics that has changed following rat eradications elsewhere in the Lesser Antilles. To do that we used a few different methods, we’re hoping that each will give us a slightly different sense for densities that we can compare one year to the next.
The first was a mark-recapture study in two different locations. We’d survey a fixed area (one of the big fig trees at the north of the island and a boulder field at the south) and catch all the lizards we could find. Every time we caught a lizard we’d write a number on its belly and put a little white dot on its backside (see below). The paint spot will help us see the lizard from a distance without spending lots of time trying to catch a lizard that’d already been caught that day.
We spent two long days marking all of the lizards we could find in the tree and the rocks. After each site had had a day to rest, we returned. By figuring out which lizards we’d previously caught and how many new lizards had shown up we can get an estimate of just how many lizards are using that area. The lizards in the tree were particularly plentiful – we’re estimating a population of around 50! with unlimited time we’d continue marking, revisiting, and recapturing a few more days but our island time was short so we compromised with a single recapture day at each site. We’ll repeat the survey next year in the same places to see if there are changes in density.
Our next survey method was the tried-and-true walk around, look on both sides of your path, and count ’em up. For this Anthony did a big hike around the perimeter of the island counting all of the lizards he saw. He did this twice and found a lot of lizards! Here’s a page from my notebook showing the track. Unfortunately the map only really makes sense to us, but as you can see, he saw 61 anoles and 65 ameiva that day. The next day he ended up seeing 73 anoles and 118 ameiva! Those are pretty wide margins, but they’ll provide a baseline for next year’s repeat transects.
Now, I decided to strap a GoPro to Anthony’s head for the second survey. It’s two hours long though so I had to speed the video up. Grab your dramamine, you’re going to need it!
This video is just a short segment of the hike in the vicinity of the “Hanging Gardens.” It’s one of the prettiest parts of the island I think. You can tell too how tricky some of the traversing is. On this section Anthony saw 10 ameiva and 24 anoles. Can you find them? I slowed down the first ameiva so you can get a good look. You’ll also notice a few other surprises along the way.