Sea Turtle Nest Inventories: What We Learn from Digging Up Nests
If you spend any time volunteering at a sea turtle conservation camp — whether it's in Costa Rica, Greece, or Mexico — chances are you’ll hear the term "PHI" thrown around pretty early on.
PHI stands for Post-Hatching Inventory, and it's one of the most important data collection tasks in sea turtle conservation. It’s also, for many volunteers, their only chance to see a sea turtle hatchling up close. But more than that, it’s a vital scientific process — one that gives us deep insight into what’s really happening inside the nests we work so hard to protect.
The Purpose of a Nest Inventory
Every sea turtle nest tells a story. And after the hatching window has passed — usually 60 to 70 days after laying, depending on the species and location — it’s time to dig it up and take a look inside.
Why?
Because just knowing that a nest was laid isn’t enough. Conservationists want to know how many eggs hatched, how many didn’t, what caused failures, and whether hatchlings were able to make it out on their own. This data helps scientists understand success rates across seasons, detect patterns in threats like predation or bacterial infection, and ultimately improve conservation strategies.
How a PHI Works: Step by Step
At Río Oro on the Osa Peninsula, we had a simple system for conducting nest inventories:
One person digs — slowly and carefully removing the sand, uncovering the remnants of the nest.
One person sorts — categorising the contents into shells, full eggs, and any hatchlings.
Everyone stays downwind — because yes, some of these nests smell really bad.
Each nest is different. Sometimes you uncover nothing but fragments of shell — a sign that the hatchlings successfully emerged and made it to the ocean. Other times, you find live hatchlings that got stuck or were too weak to climb out of the chamber. In these cases, we help them to the surface and watch as they scurry toward the waves — a moment that never gets old.
In areas with high temperatures or heavy daytime predation, biologists might care for these hatchlings until the cooler hours of dusk, when it’s safer to release them.
Sorting the Nest: What We’re Looking For
The sorting process is both delicate and detailed. Each egg is checked and placed into a category:
Empty egg shells – signs of successful hatching
Dead hatchlings – those that didn’t survive the emergence
Unhatched eggs – these are inspected to determine why they failed
This last group often involves cutting open the egg with gloves on. Inside, you might find:
Early-stage embryos
Late-stage hatchlings that didn’t make it
Eggs with bacterial rot or signs of predation
It’s not always pleasant. Decomposing eggs smell foul, and some nests are full of maggots. But each piece of information is crucial — because it helps conservationists refine their strategies and gives a more complete picture of what these turtles are up against.
Beyond the Hatchlings: Nest Metrics
The inventory doesn’t stop with the eggs. We also measure:
The depth and diameter of the nest
Its GPS location and position on the beach
The surrounding environmental conditions
Any signs of disturbance (crab holes, flooding, predators)
This data adds context to the hatching success — helping identify, for example, whether nests laid too close to the high tide line are more likely to fail, or whether certain zones on the beach are more prone to bacterial infections.
Completing the Cycle
Once the inventory is complete, we rebury everything left in the nest. This might seem odd, but it serves an ecological purpose. Sea turtle eggshells and unhatched material decompose and return nutrients to the sand dunes, helping to sustain the fragile beach ecosystems where turtles nest year after year.
It’s a small but powerful reminder of how these creatures — so often associated only with the ocean — are also tied deeply to the health of the land.
Why It Matters
Nest inventories might not be as dramatic as watching a mother turtle lay her eggs, or as heartwarming as a mass hatchling release at sunset — but they’re one of the most important tools in the conservation toolkit.
They reveal what’s working, what’s failing, and what we still don’t fully understand. And they give every nest a final moment of attention — a way to honour the life within it, even if it never made it to the sea.
As a volunteer, participating in a PHI connects you to the science behind the work. It’s not always glamorous, but it’s meaningful — and you come away with a new respect for just how much has to go right for even a single hatchling to survive.
