Field Notes from Tetiaroa: Biodiversity Quickly Recovering

IOCC Project Tetiaroa Atoll hosts a diverse array of wildlife and are critical nesting habitat for French Polynesia’s seabirds, Green Sea Turtles, coconut crabs, other native plants and animals. Surrounding the island, protecting it from ocean swells, and sustaining its lagoon and terrestrial ecosystems is a healthy and vibrant coral reef.

Unfortunately, invasive rats threatened this rich biodiversity, significantly reducing a once-thriving seabird population which impacts both terrestrial and marine ecosystems. Tetiaroa Society and Island Conservation worked together to remove invasive rats in 2022, and the work is on-going. The partners remain dedicated to protecting Tetiaroa from invasive species so native plants and animals can thrive for generations to come.

Field Notes from Tetiaroa: Biodiversity Quickly Recovering

By: Frank Murphy, Tetiaroa Society Program Director

Crabs!
Only five months after rats were removed, the Fiddler Crabs are back and we can expect them to repopulate mudflats across the island! Tetiaroa Atoll Restoration Project researchers Jayna DeVore and Simon Ducatez rarely saw Fiddler Crabs on island — until now. These crabs have almost certainly been present on Tetiaroa for a very long time, but must have been a favorite delicacy for invasive rats.

These beautiful little crabs are found throughout the tropical Indo-Pacific and have a major impact on wetlands, sieving out detritus and aerating the sediments. For careful observers they also put on a show, with the males dancing outside their burrows, waiving their large claw, all to attract roving females. When the female crab makes her choice, they dash down into the safety of his burrow to lay and fertilize eggs.

Masked Boobies!!
Last year, we reported that a pair of Masked Boobies had laid an egg on one of the northern beaches of Tetiaroa. This was news since this has never been observed before. We had high hopes that a new (or returning ancient) species might be added to our seabird population. But the first egg was lost to predation (possibly by rats, as was often the case for the related Brown Boobies), and the second was infertile and was eventually abandoned by the parents.

However, the couple came back and laid two eggs which hatched last October. Seabirds raise one chick at a time, and so nature took its course and unfortunately one of the chicks died. But the other one is now well on its way to being an adult. The couple returned again this year and has successfully hatched another chick.

Without invasive rats to disturb them, Masked Boobies are now free to establish a colony here, which would be the first one in the Society Islands.

White Terns!!!
Just a year after the initial rat eradication our bird researchers reported a 100% increase in White Tern nesting.

This was not necessarily because more birds showed up, but more likely that half the nesting pairs that were here failed to set up a nest because of rat predation. When we say “nesting” it is a bit of a misnomer for this bird since the females lay their egg right on a branch, with no nesting material at all.

When the chick hatches it somehow gets out of the egg without falling off the branch, and then just grabs on with its already large feet. There it sits for a couple of months being fed regularly by its parents until it begins to fly and venture out on its own. These small birds were easy targets for rats, both as eggs and chicks. But with rats gone their chances to reach adulthood are very much increased.

Post-eradication we expected a recovery of the population, but wow, this is fast. At this rate, as young become reproductive in a few years, we can expect to see a LOT more white terns on the island in the near future.

Fiddler Crab, Masked Booby, and White Tern Photos Credit: Simon Ducatez

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