Where have all the 'guanas gone? Long time passing.....

Solar Encounternet tag.

Once upon a time, a calibration study commenced. A small group of interacting Ctenosaura similis were chosen to sport solar tags that received and transmitted signals when animals encountered each other.

Thin Yellow-Brown-White after laying her eggs.

The scientists hoped they would wear the tags for about 6 weeks, after which they would be removed. In the beginning, all was well. But slowly, females in the study disappeared. Their radio signal strength indicators weakened and simply seemed to stop working.

Troubleshooting was impossible with no signal. Suddenly, female iguanas with no beads and no solar tags began nesting everywhere -- along the old airstrip, along the slope of the football field, in a dirt mound, in open areas of tilled soil.

Soon, a missing tagged iguana re-appeared, thinner, but behaving normally. Then the second missing iguana came home, also skinny. Between these two events, two other females left the study. By now it was obvious to the scientists that iguanas were laying eggs a bit earlier than reported in the literature.

Study males decamped from their breeding territory and seemed uninterested in pursuing copulations. Younger and smaller iguanas appeared, in crevices and on walls, potentially joining their larger adult counterparts. The social system was in flux.

Lighter brown soil of iguana nesting area.

C. similis head appearing out of nesting burrow.

Green iguanas, Spiny-Tailed Iguanas -- everyone was laying eggs, moving, closing down this chapter and readying for the new one.

White-White-Brown Returns!

C. similis nesting mounds

It may seem odd to declare the return of a missing iguana through a photo of nesting mounds -- but our best guess is that White-White-Brown, gone since 2/5/16, was off laying her eggs. Her return and sighting today showed us a healthy-looking but thin iguana. Tag intact, attached to her body, solar battery well charged, all is good.

Female digging her nest.

WWBr looking thin yet healthy! 

WWBr

Part of calibration and deployment means attempting to understand how well tags work and endure the natural inclination of C. similis to shove themselves into small rock crevices, dead tree limbs, and all sorts of human-created refuge spots. We now have proof that nest digging does not damage a tag, and that the natural pattern of digging and resting will keep a solar battery charged. Or, at least in the case of WWBr, it works!

Of nine tagged animals, two are male. Of the seven female, two are missing with no tag radio signals. We are hopeful they, like WWBr, will return in good health, simply behaving normally.

Week Four: In which things go wrong...but also right

Yellow-Green-Yellow comes down Big Tree.

By mid-day on 5 February, we had deployed eight working tags on iguanas. A ninth tag, #3 wasn't charging correctly and had to be placed in a lower power mode.

On 10 February, tag #5 on White-White-Brown (WWBr) went Missing-in-Action, along with the lizard. We hope she is off on a great adventure and eventually returns. Her tag send no signal which may mean it is dead, or simply out of range.

White-Orange-Green, the famous WOG of this blog, decided there was little reason to come out and bask for almost a week. We watched with trepidation as her battery voltage drop. Luckily, WOG decided it was time to reappear -- and her battery is charging fine.

Every day we get up before dawn and download logs from the base stations. The logs are the physical proximity encounters between animals, all to understand their social structure. Base stations also record "pings" from tags so we know when and generally how far tag #5 was from any base station when it and WWBr went missing. Each base is managing to successfully "talk" to tags, receive log downloads, and cover a good physical area.

PBKR

 Of course after bringing tag #3 to a good charging level, and spending two days trapping an animal that interacts with the tagged group, Pale Blue-Black-Red (PBKR), our twice daily voltage checks revealed the tag was again not keeping a charge. So, back into a low power mode.

To help understand the data logs, we are processing a number of days by hand. 8 days and ~7 tags is roughly 25,000 lines of tag-to-tag pairs, by day, time, and radio signal strength. It does tell a story!

Week Three: The System is Live!

Base Station location map.

At some point, our testing had to end, parameter decisions needed to be made, and the system to move from enclosed indoor place on to live animals in their habitat.

Base Stations were located near the group of animals we planned to tag and monitor. Two weeks of calibrations, a few days for percolation of plans, and we were ready to collect real data.

Solar Encounternet tag

Next task was trapping eight iguanas -- and luck was with us! We managed a dominant and subordinate male, and six females of varying personalities. Some are bold while others much more shy. The group, tagged in less than 12 hours, went live on 5 February 2016.

Another stream of issues: would the tags stay on the iguanas? Would we see lizards itching at the tags, suggesting they were annoying and changing their behavior?

The tags are powered by solar panels with the expectation that the natural basking behavior of a Spiny-Tailed Iguana would keep them charged -- would they really work that way?

Would the iguanas visit areas near enough to base stations to ensure proximity log downloads?

Will the raw data make any sense?

Like all new endeavors, getting over one hurdle simply means time to get ready for the next mess.

To save battery power, tags enter a "sleep mode" at the end of an iguana day, and the Base Stations follow an hour latter. This is reversed in the morning. I set clocks, download logs, and check battery levels starting at 5:30 am; tags awake at 6:00 am.

For the first week, it's important to see what Bases are being used by which iguanas, and making sure all animals are downloading interaction logs. We are mostly in good shape except for one iguana who does not seem to have come out of a hide in a couple of days. Tomorrow the hunt is on!

Rusty, our dominant male, wearing his tag. 

Week Two: Tags, and Bases, and RSSI, oh my!

Base Station on 3 meter pole with Megan Heier. 

Calibration. Our dear friend Wikipedia offers this explanation: Calibration is the process of finding a relationship between two quantities that are unknown (when the measurable quantities are not given a particular value for the amount considered or found a standard for the quantity). 

I am using Encounternet radio frequency identification tags on Spiny-Tailed Iguanas. When the iguanas are within a certain physical distance of each other, the tags will log their encounters. What needs to be calibrated is the relationship between distance and Radio Signal Strength Indicators (RSSI).

If the RSSI between two tags (soon to be attached to actual iguanas) is -11, how close are they to each other? What about when they are +7 RSSI?

How close does an iguana with a tag need to be to a base station to ensure a power-efficient download of physical proximity logs? 

What height of the base station ensures the above, 3 or 1.5 meters?

When the antennas go in the same vs. opposite vs. perpendicular directions from each other, what does that do to RSSI?

Where should the base stations be mounted?

When should we log tag interactions (wake up call) and when should we stop (bedtime)?

Which iguana sub-group would be useful to test the calibration on real animals? (This is not a trivial consideration -- it would be good to have different personalities, sexes, and perhaps not too many animals that climb 20 meter trees....)

So, we've attached base stations to different height PVC poles, marched tags up and down a measuring tape in the hot sun, taking numerous pages of data. And as explained, RSSI is stronger when off the ground (lizards with jet packs, anyone?), away from concrete and piles of rebar,  and best if antennas are parallel and facing each other.

We have mostly learned how to set controls in the system software, have a good idea of which iguanas will get tags, and are almost ready for a real run.

Rusty, a large male who patrols the open area in the above photo, has more than 8 females in his territory. He also has several second-rank males that he has to address, running them off as needed. The females are bold and shy which should also help test the system and begin to answer the question, why do these non-cooperative animals have the social structure they exhibit?

Week One: Census!

Kaplan on the prowl.

Our first field week is over and we're off to a good start. Megan and I arrived in the dark at the Organization for Tropical Studies' Palo Verde Research Station, Palo Verde National Park, after a long travel day on January 18th. We ate a vry late dinner, provided some mosquitos with a meal, and went to bed.

We spent the next day getting our processing lab assembled, settling our rooms, and scoping out resident iguanas such as Kaplan, the largest male at the station. Marked in 2013, he still sports his original beads, Blue-Yellow-Brown. As mating season is in full swing, Kaplan is bold, making important circuits in his home range, chasing off male interlopers, and copulating with females.

Our next reentry into the field is the process of trapping iguanas, checking them for PIT tags, and rebeading if they are a known animal. If the lizard is new, we take standard morphometric measurements, a blood sample for molecular analysis, especially genetic relatedness, and assign a bead code. Important for our work is monitoring the stability of the social group (very) and seeing in what ways an animal has changed its routine, moved refuges, or otherwise is behaving differently than August 2015.  

Rebeaded White-Yellow-Black

 

Since 2013, more than 110 lizards have been caught and beaded in the research station. We track how many new animals we see per day to understand how long it takes to observe a large majority of marked animals. It's a natural expectation that some animals will disappear through predation or emigration. Likewise, younger animals are establishing refuges within certain areas while males are more evident as they seek resident females. Adults males sometimes immigrate into the area. And, lizards move to different refugia within the site.

For example, last July and August, White-Yellow-Black (WYK) used a pipe to sleep in right in front of the OTS office. This trip she is no longer using that pipe and has only been observed in a small woods patch in front of the researcher dorm, about 15 meters away from the office. This may be a temporary or permanent refuge change; we don't know. On the other hand, this is not a large move and WYK is interacting with the most of the same animals from the July-August 2015 observation period. 

When we see a move such as WYK we also try to find the refuge as this is the place where we may quickly check each day to see the animals is still in the group. It's rather helpful that Ctenosaura similis is routinized!

When the semester break began in early December, I thought I would accomplish a good bit of prep and back-burned projects before departing to Costa Rica on 1/18/16. No such luck! While I did visit family for a long weekend, I immediately followed it with a great sinus infection. I then was healthy for SEVEN whole days, presented at #SICB2016, and then caught the flu that I am still fighting. What a rumble!

Given that we leave in just a few days, it's time to get on with all things SCIENCE and Costa Rica! Without further ado, let me introduce Megan Heier, my field assistant for this trip. Megan will help optimize the Encounternet system for use on the spiny tailed iguana (C. similis) as well as numerous other field jobs. This is the first time the system will be used on an iguana -- while the headaches are sure to come, it's also going to help fill in a small part of the secret social lives of lizards, Plus, it's Megan's first time traveling out of the United States -- should be a great adventure for all concerned!

Megan Heier is a junior biology student at UNC.  She is originally from Colorado Springs and has found that Greeley is not nearly as stinky as she always had been told.  She is interested in animal behavior and is exploring her future career options in research. Her hope is to eventually pursue a PhD in biology, but her specific area of study is not decided.  She has only ever met one iguana named Izzy who had a passion for hibiscus and going on walks.  Besides school, she loves taking care of her rats and elderly mouse, watching sitcoms, and spending an inordinate amount of time bird watching.