Acutus a button

I recently spent a couple of days on the island of St. Croix to capture Anolis acutus, a species endemic to the island and closely related to the trunk-crown anoles of Puerto Rico. It was a great trip, and there were lizards everywhere. I stayed at an organic farm in the "mountains", and, as part of the deal to stay there at a very low price, when I wasn't catching lizards I helped the owners pick fruit and hoe their gardens. I had a good time doing it, and I never had to go to the grocery store! Now I start my last round of sprint trials before heading back to NC.

Exceptional Hunters

If you have been keeping track of our trip, you know by now that Leiocephalus is a major player in our study. I have commented before on a few aspects of their behavior, including their foraging. The movie below (exerts from a longer movie), courtesy of Dave, shows that Leiocephalus are exceptional hunters. Having the behavioral flexibility to forage on bugs, lizards, flowers, and fruits is already pretty impressive. But this observation tops all the previous ones. Furthermore, if you had thought that anoles might be able to escape from the jaws of a Leiocephalus, you might need to reconsider. The video clip is from a curly-tailed lizard that was foraging at the intertidal zone and came a across a "mangrove crab". Mangrove crabs have somewhat square & hard carapace, can move relatively quickly, and can use their claws effectively. However, curly-tails are the "tigers" of the cays, although their diets might be a little more diverse.

Tools of the trade II

A recent discussion with JBL on the pros and cons of different methodologies used to measure dewlap spectral properties has prompted me to write this post. I would like to begin by stating the obvious: you should take my words with a grain of salt. None of my graduate students have followed in my footsteps to work on dewlap color, which might speak volumes about their perception of my expertise on the subject.

As a post-doc I had the honor to learn how to collect spectral data from "El Jefesisimo". However, by no means should Leo be blamed for my lack of skill. Over the years we have built a nice number of gadgets with the objective of getting those elusive "perfect" measurements. In the case of dewlaps, I am referring to a nicely extended dewlap, in which the surface is flat (i.e., scales are not irregularly arranged due to way the dewlap is being expanded, thus avoiding the possibility of specular reflection), the dewlap is not pressed against any surface (to avoid the problem of having different distances between the probe and the surfaces of the dewlaps), and the dewlap is not over-extended (which can result in an increase in brightness … and by the way, lack of full extension or compression of the dewlap results in the opposite problem -- you may begin to think that you have a dewlap that is darker than it really is). Note, in the case of the anoles dewlap the pigments are not limited to only the areas between scales, as illustrated below by a histology prep of the dewlap of A. cristatellus pigments are also present within the scales.

As I learned very early on in my attempts to measure dewlap color, one of the major pitfalls of using a spectroradiometer (yes, the correct term is spectroradiometry, not spectrophotometry) is that those gizmos don't come with a "garbage" detector. Therefore, they suffer from the “garbage in, garbage out syndrome”. In other words, the quality of data is directly correlated with the quality of the surface being measured. You will always get a spectrum by measuring any surface; the question is how good of a representation is that spectrum. I have convinced myself that the best method to hold the dewlap is by having it extended with a gizmo like the one shown in the photo below. It is not perfect, but is as close to a natural extension that I have been able to achieve. Also, I can easily control (and actually see) the location of the probe without any need to guess.

I have also tried holding the lizard by hand and expanding his dewlap sideways and take spectrums by using the probe-holder sold by Ocean Optics to hold the probe in place. There are two problems with this. First, it is impossible to accurately know where the probe is located (I don't like that). Second, the holder is so heavy that it tends to change the surface of the dewlap (i.e., scales can change their arrangement and the dewlap gets a funny looking bend on the area on which the holder is located) I am not a big fan of those two possible sources of noise.

The other important component needed for measuring dewlaps is the light source. If possible, my preference is to use a Xenon-Arc lamp. Those are great, a nice continuous spectrum similar to sunlight and with sufficient energy across all the relevant regions of the spectrum. Moreover, in the lab I can use a radiance probe, which is more accurate than a reflection/backscattering probe. However, it is impossible to bring those to the field. Thus, in the field I mostly use a xenon-flash -- not the best -- but it does a relatively decent job. If you are using flash, then you must use a reflection/backscattering probe. A note about using those probes: they are composed of multiple fibers, and the light source must be connected to the outside ring, while the recording fiber (a single center fiber) is connected to the spectroradiometer … not the other way around! The probe is designed to create a somewhat diffuse light spot and to collect data from the center of the circle. This means that, in reality, you are only sampling the center of the circle. Which should be equally illuminated by the diffuse source. Also, in the case of reflection/backscattering probes, the distance between the probe and the surface must be kept constant because measurements are sensitive to distance. It probably goes without saying that the diameter of the circle will change as a function of distance to the surface being measured and thus the measurements.

This may simply be the deranged rambling of a grumpy old man, but I hope it is of some help.

Tormenta

The lousy weather continues. Yesterday we had a productive morning, but during the afternoon big dark clouds decided to make their presence felt at Snake Cay. Today, more of the same, a storm is seating right above us and there seems to be no end in sight. It is going to be down to the wire to get those last few observations.

Cocinando con Maria y Angela

We had bad weather this afternoon -- windy, completely overcast, and relatively cold -- which put our data collection on hold. However, the bad weather provided an opportunity for El Jefe to teach Maria and Angela how to prepare some authentic Puerto Rican cuisine. The lesson of the day: the highly popular and easily prepared "tostones." Both Maria and Angela quickly became experts at making tostones.

Tools of the trade

After a few years of collecting behavioral observations under natural conditions, our "tools of the trade" have evolved with our methodology. We currently use mini-DV camcorders. After a period of testing, we are very pleased with our current set-up. I am a fan of Canon. So far our camcorders have sustained a considerable amount of "not so friendly" treatment, and they keep clicking. I should probably point out that I don't get any free equipment from them, although I wouldn’t mind being sponsored by them. Also, I like the fire-wire option, which allows for easy and fast playback on computers. You can call me old fashioned, but I am not a fan of the new digital hard-drive cameras. When you are recording hundreds of observations as we do, tapes provide a much friendlier way to store the data.

We have two distinct combinations of equipment. For our work on time-budgets, our “set” consists of (a) a mini-DV camera, a small compact camera with a manual focus option that is admittedly somewhat awkward, but useful for the occasional need to focus in on the lizard; (b) three extended life batteries, total recording time 10 hrs; (c) lightweight monopod with quick-release plate; (d) plenty of empty tapes, we can fit 4 extras inside our cases; and (e) a trusty water-proof & impact-resistant Pelican case. You might think, “there’s no need to use a mono-pod with such a small camera.” Well, think again. When you are trying to follow lizards for an extended period of time, anything that helps to increase the steadiness of the footage is a must. In addition, the set contains a Rite-in-the-rain notebook, tailor’s measuring tape, and mechanical pencil. This is a small compact set, which fits inside most backpacks and can stand the daily pounding, including occasional ocean spray, rain, heat, and the occasional drop of the backpack or Pelican case.

For our work on the physical properties of head-bobs displays, our equipment gets a little more complex. Again, we use (a) a Canon -- this one is our work-horse, with Hi-Definition recording and manual controls (such as the focusing ring that is quick and reliable); (b) sturdy tripod – you can’t get good videos for this type of work with out a stable tripod because the slightness shake prevents accurate quantification of head movements; (c) sturdy quick-release tripod head -- after using a few different types, we have found that the ball- type works best as it’s easy to use and carry around; (d) extra-batteries -- enough for 12 hrs of videos; (e) a large Pelican case that is big enough to fit the camera, tapes, batteries and tripod head; (f) an anemometer -- this one has a separate Pelican case; (g) a digital range finder, which is also transported inside its own Pelican case, and (h) our trusty ping-pong ball. This set is a little heavier than the other, weighing altogether approximately 20 - 25 pounds. However, again, we have found what seems to be strong enough to survive in the field, here under salty conditions or in the rainforest, while also collecting high quality data. Note, this set is approximately ten times more expensive than our focal observation set. Thus, if you are not interested in very fine details, there is no need to go overboard with something like this.

Foraging Extravaganza

In anoles, as is the case for most reptiles, most of what we know about their diets comes from studies of stomach contents from museum specimens. Over the last three weeks, we have observed brown anoles capturing a diversity of prey items. Below are a couple of video clips of anoles foraging on prey items that I found somewhat surprising. The first one shows a male foraging at the intertidal zone during low tide. Our observations indicate that anoles commonly visit the intertidal zone where they forage for marine isopods. YES, marine isopods, which I am guessing might have a high salt concentration, which raises interesting questions about possible physiological mechanisms to deal with salty prey. The use of the intertidal zone occurs more often in cays where curly-tailed lizards are absent.



In the second video, a male brown anole is foraging up in the "canopy" and tries repeatedly to eat a small berry. Interestingly, or maybe not, we have observed this behavior (i.e., foraging for fruits) on islands where curly-tails are present.