A visit to Christmas Island

Last week I ventured to Christmas Island to discuss my research with other scientists and staff from Park Australia. This was my first trip to the island and I have to admit, I hope it won’t be my last!

Christmas Island is a Australian island in the Indian Ocean, far away from the Australian mainland and closest to Java. It is only 135 square kilometres but harbours a multitude of native and endemic wildlife, like seabirds, reptiles, a flying fox (and most fascinating to me) 20 species of land crabs of which I was lucky enough to encounter four. The most iconic of these species must be the red crab, which migrates in masses to the beaches in the early wet season to lay their eggs.

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Red crab – not migrating just hanging out and probably searching for food

As mentioned in a previous post, invasive species, especially feral cats, may have caused the extinction of native species on the island and continue to threaten its biodiversity. For this reason, cat control had commenced in residential areas of the island in 2010 and was extended to the entire island in 2015, resulting in the removal of around 950 cats so far.

Although the vast majority of cat control programs is very successful, in a few cases control of these top predators has led to unexpected flow-on effects. The eradication of cats on Macquarie Island led to an increase in the rabbit population leading to a change in the habitat structure. The effects of an eradication can also vary in different habitats on the same island as it happened on Little Barrier Island, NZ, where the eradication of cats led to increases in the population size of Pacific rats, but only in high altitudes. My research and the research of our PhD student Rosie Willacy (co-supervised by Sarah Legge and Eve McDonald Madden) will investigate if the decline in cat abundances could lead to a change in the black rat population or if it does not affect this invasive mesopredator.

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Rosie checking her motion cameras on a ground-breeding bird’s nest.

But Christmas Island has many more ongoing research projects!

In my week on CI, I was lucky enough to attend a “Meet the researcher” event organized by Parks Australia for the community to hear about the current research on the island. There, we were presented with work on the biocontrol project on yellow crazy ants that aims to reduce the scale insect population that enables the YCA to form supercolonies.

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Breeding facility for the yellow crazy ant biocontrol agent

An update on the cat control program was given by David Algar (Western Australian Department of Biodiversity, Conservation and Attractions) and Parks Australia employee Caitlyn Pink, who positively surprised me with her finding the diet of black rats on the Island is largely herbivorous.

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Cage trap for cat control.

Another amazing achievement is the captive breeding of the Blue-tailed skink and the Lister’s Gecko, two reptiles that are extinct in the wild but breed well in captivity. The aim is to release them once the population is high enough and the research on predators and a new disease is finished.

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Blue-tailed skink at lunchtime

From Mark Holdsworth, we heard that CI Goshawks like are best lured with teddy-bear legs and there more research on many other species and aspects, giant geckos, the ecology and health of flying foxes and the question of how the crabs made it to the land is being studied as well.

Overall it was a really educational and enlightening week for me. I learned a bunch about the environment on Christmas Island, was finally able to put  faces to peoples names and voices who I previously sole conversed via email or phone and I got reminded about the difficulties of field work (e.g., those times when the flash on your motion camera is too bright despite the black tape across most of it). Personally I made some interesting discoveries, such as that proper free range chicken like those found everywhere on CI sleep in trees at night and that there are birds that parasitise on others for food.

I’m already looking forward to the next trip, with results on my research and hopefully with a snorkel in my luggage.

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