Reading Sea Turtle Nests
Just as in learning to read a book, one first learns letters, then small words, long words, short sentences, and finally, as word and syntax attack skills grow, the whole book. Once we locate a sea turtle crawlway, we read the sign to determine if it represents a non-nesting crawlway or probably represents a nest, we “read the nest” (ie. examine the morphologic clues which were left behind during the nesting attempt).
In this process we first document the probable nest by measuring and sketching, forcing ourselves to rigorously observe the individual traces left by the turtle during the nesting attempt. These observations are recorded in our field notebooks using a nest template and a scaled sketch. It is imperative to record this information before disturbing the nest by digging because the act of digging effectively erases most of the evidence.
Field sketch of Loggerhead sea turtle nest at two scales to depict the nests’ position on the beach (right), depict the morphologic detail of the nest (left), and to depict the position of the egg chamber discontinuity within covering pit. Note that this turtle dug two body pits before she succeeded in nesting on her third attempt [95-104]. The nest template is seen printed on the other side of this page.
Field sketch of Loggerhead sea turtle nest [00-091] at three scales to 1) depict nests’ position on the beach (left), 2) depict the morphologic detail of the nest (middle), and 3) depict the detail of the egg chamber discontinuity within covering pit. Note the crawlways are the same length because their lower ends were “erased” by latest High Tide after deposition of nest.
Once these data are recorded we put ourselves in the place of the turtle and write a description of the turtle’s nesting behavior from her crawling onto the beach, through the nesting event, to her egress from the beach.
Using these the three parameters of nest morphologies, the nest above might be described in the field notebook as:
“A simple, backbeach, obstructed nest; obstructed by impingement upon steep storm scarped dune ridge. Entrance and exit crawlways equal length due to erosion of lower parts by last high (Neap) tide; entrance crawlway on the south, exit crawlway on the north. Turtle crawled in perpendicular to scarp, crossed high tide wrack, turned parallel to storm scarp, pitted and deposited clutch, covered as she scooted forward, rotated 90o and exited the northeast edge of the covering pit, and crawled back to the sea parallel to her entry crawlway.”
At this point (2007) we are normally able to predict the position of the egg chamber based on the description of the turtle’s nesting behavior.
Reading the Nest
The observations are recorded in our field notebooks on a nest template and as a scaled sketch. It is imperative to record this information before disturbing the nest by digging because the act of digging effectively erases the evidence.
This process decreases the amount of work we do to validate each nest on St. Catherines Island. If we correctly predict the location of the egg chamber, we can excavate through a smaller volume of the disturbed sediment of the nest to expose the discontinuity of the egg chamber neck with the surrounding laminated beach or dune sediments.
Clues used to identify direction of entrance include V’s left by the flipper claws, plastron drags made as the turtle leaves the nest, thrown sand and flipper scarps made during covering, and crisscrossing of exit over entrance crawlways.
Validating the Nest
The first step to validate a nest is to determine if one has a non-nesting crawlway or a possible nest. Non-nesting crawlways will often be simple loops or extensive wandering patterns with no disturbed “nest areas.” If you think there is a nest present, or if you can’t tell there isn’t a nest present, then you must excavate the possible nest.
It is absolutely necessary to identify the entrance and exit crawlways, because once a turtle has nested, she will immediately return to the sea (unless severely disoriented). Therefore one could follow the exit crawlway inward to determine if there is a disturbed (bioturbated) covering pit present, or as a good alternative, follow the path of the turtle to sequentially ‘walk through” her activity, being sure to keep off the crawlway to avoid destroying the evidence.
Once the covering pit is located, carefully excavate the loose (bioturbated) sand out of the entrance to the covering pit [that means outside the limiting edges, so you don’t have to move the sand twice!] with a small shovel, a trowel, or a cabbage palm frond. Remove the loose sand a few centimeters at a time, following the contact between the loose sand above (that was stirred up by the turtle’s activity) and firm sand below (the surface of the undisturbed beach). The texture of the sand and the sound of your scraper will help you excavate. Once you find the contact between the loose and firm sand, follow it forward along the mid-line of the crawlway entering the covering pit. About ½ a turtle length into the covering pit, you should find the bulls-eye of the egg chamber discontinuity… if everything works as it should.
Decision Tree for Reading and Validating:
- Is there evidence of nesting?
- Elliptical Covering area?
- Thrown sand?
- Interest by potential predators?
- Time on Beach (D crawlway length)?
If Yes: [drum roll here]
- Direction turtle crawled.
- Opening V’s in crawl direction?
- Push marks, steep faces at back?
- Cross-cutting Relationships?
- Identify the entrance crawlway.
- Identify the exit crawlway.
- “Walk” through turtles’ activity.
- Predict position of egg chamber.
- Excavate from entry of body pit,
- Follow bottom of covering pit in,
- Scrape bottom HORIZONTALLY
- Locate egg chamber discontinuity
Jacob Staff scale is 5 feet (1.524 meters).
If the turtle didn’t nest immediately, or if she hit an obstruction during construction of her body pit, the egg chamber may be offset, or even in another part of the covering pit. In this case, carefully follow the base of the pit to determine in which direction it is deepening … that will be the likely direction of the egg chamber. In the most extreme case the entire bottom of the covering pit may have to be scraped.
If there is a heavy mineral deposit, the egg chamber neck will likely be masked by it. Sometimes a judicious search with a foot will locate the egg chamber neck as the foot “falls in” to the loose sand filling the egg chamber. Obstructed nests will often present the clutch of eggs in very odd placement, tucked under adjacent wrack mats, beneath clumps of grass, or alongside, or under, buried logs. Good luck with that!
If you can’t find the clutch of eggs, you don’t have a nest! The normal time spent in an unsuccessful search is about 45 minutes, followed by [sigh] probing. Occasionally what looks like the covering pit will be separated from the body pit … by a wrack mat, a log, or even a dune ridge, so scan the entire area for these possibilities.
If you miss a clutch of eggs, chances are so will the predators, and the nest will likely appear as a “wild” nest in about 60 days.
The search method of last resort on St. Catherines Island, and the one most often used on other Islands, is probing. Probing is using a stick or rod to located the egg chamber neck by its difference in softness, the bottom of the covering pit is traced systematically by gently probing until the probe drops into the egg chamber neck. We chose not to use this method because the potential damage to the eggs is much greater than in scraping, and, of course, we have those wonderful laminated sands to use as our geologic guide to nest morphology!
Last updated: 12/15/2014