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.

2016: Field Season!

Iguana refugia -- also known as a gutter.

December 1, 2015 -- I am counting down to January 2016, my first long trip to Palo Verde (nine weeks). Along with a field assistant (stay tuned for her introduction in a future post!), I'll be testing an Encounternet System on the iguanas to gather a much fuller social network based on physical proximity.

First we will test how the Encounternet system works at our actual study site. We will simulate iguanas climbing trees, disappearing into dry forest patches, or feeding on open areas. Once we have calibrated the system, a small groups of iguanas will try out the tags in real time, eventually scaling up to a full deployment on 30 animals.

This will be an important window toward understanding how non-cooperative animals negotiate their social lives and is part of the first studying considering the social network in and egg-laying, neotropical lizard.

Introvert? Extrovert? Ambivert?

 To understand the Spiny-Tailed Iguana's personality, I'm testing them in the field. One such examination is called the Open Field Test (OFT). Its origins reside with the fear perceived by some rodents when they can no longer touch their world -- when they are in the open, likely at greater risk of predation.

Theory suggests that bolder animals will explore the open area more than will shy animals. This makes some sense if you prefer to hug the sides of your world, touching physical objects. In Ctenosaura similis, an omnivore that often feeds in open areas, how useful is the OFT to measure fear -- and is there a statistical difference between bold and shy iguanas in their exploration of the OFT arena? Does Bold Pale Blue-Black-Red (PbKR) explore the arena more than shy Brown-Red-Green (BrRG)?

PbKR: Bold

BrRG, on tree roots near the pergola. A very shy iguana.

 To begin to answer that question, I constructed a 10' x 10' testing arena, seen below, and rigged a digital video camera on the station ladder to record 10 minutes of exploration per animal. I use an imaging tool to superimpose a grid on the area and score how many times an animal crosses the grid as well as other behaviors (jumping up sides of the walls, attempting to climbing the ladder, sitting, etc.

Open Field Testing arena with tripod on ladder to digitally record test.

It may be that bold and shy animals have similar levels of exploration because the OFT is not a good test of fear in this species. They may all be equally irritated from the loss of a visual field and spend energy searching for an escape route. While it would be fruitful to have personality tests that work for all taxa, this strikes me as unlikely -- especially in an animal that often feeds in an open field!

White-Orange-Green (WOG) grazing on the lab lawn (open field).

My How You Have Grown!

Black-Black-Green (KKG), fondly called Keg, was first captured 24 December 2014. He weighed 250 grams, and measured 15 cm from snout to length of his body. His full tail was 34.6 cm in length.

On 21 July 2015, I recaptured KKG. He only has 7.3 cm of original tail and 12.3 cm of regrown tail -- did he survive a predation attempt or did he injure the tail in some manner? His Snout-to-Vent length is now 20.4 cm and he has gained 350+ grams of weight. You can see how my hand is holding a much larger iguana than in December!

Keg is growing quickly. He has survived the perils of being a tiny hatchling predated on by almost every other animal. He is still living in the same general area, using the office roof for a refuge and feeding on the lawn in front of the lab. And he is interacting with iguanas larger and more experienced than himself.

How dry is it?

When I use fruit to bait the iguana traps, I may instead catch a capuchin monkey or a coati. This year the rains are very late, the soil is crunchy, and the leaves are wilted on the trees. 

Here is a begging capuchin who followed me on hopes of food. While they do raid traps, this is not typical in the station. 

http://youtu.be/b-6Sbi9Jg2E

And here is a male coati who also raided one of the traps:

http://youtu.be/O90LjkQYLeo

I won't bore you with the raccoon;  or that this post was delayed as I needed to release another monkey from another trap. When a troop is around, trapping stops. 

Below is a yearling iguana ignoring small trap while WWW goes for the big trap -- she was rebeaded and I took a blood sample for the molecular part of my dissertation:

http://youtu.be/3Wp0iNOWJj4