Brown Noddy Census and Green Turtle Season

Sooty terns landing amongst the plastic models

With Janske & Martijn going on their one month leave at the end of May, it was up to Tommy and me to keep things ticking over on Denis Island. We began to carry out island tours and evening presentations for the hotel guests. Whilst enabling us to improve on our knowledge of the island, the tours offered us an opportunity to interact with guests. We are able to chat with new people on a regular basis. Given we are on an isolated island where we recognise almost everyone; it does make a welcome change (although we ran into a few troubles with guests who didn’t speak English. I tried my very best to remember my basic GCSE French to no real avail).

Tommy and I carrying out brown noddy census

June marked the start of the south-east winds breeding season for the Brown Noddies (Anous stolidus). In around early May we could see these seabirds in much higher abundance than usual all flying around the beach looking for seaweed to help build their nests. Despite the increased amount of guano raining down upon us from above, it was fantastic to have these beautifully slick seabirds back in high numbers on the island. Brown noddies tend to nest in coconut palm trees and very occasionally in coastal casuarina trees. We saw them in high abundance around the hotel where palm trees line the entrance to the hotel reception.

Given we had a skeleton GIF crew on Denis Island, Jennifer from the GIF head office arrived on the island for a couple days in mid-June to help out with the Brown Noddy census. The previous census conducted in February/March during the North-west monsoon season counted close to 350 nesting pairs, during this census we counted the exact number of nests on each active tree which was a very time-consuming exercise. This time around we counted the number of active trees in a given area and chose 2 or 3 ‘candidate’ trees to count the exact number of nests. This way we could use the candidate trees to calculate the total number of active nests in a given area and over the entire island. We calculated roughly 361 breeding pairs on the island but with many individuals roosting as well the overall population on the island is much larger. The number of breeding pairs was similar to the North-West monsoon season despite these being most probably a separate breeding population.

Tommy, me and Jennifer during the presentation

Along with the noddy census we carried on with the turtle monitoring. The green turtle nesting season on Denis Island lasts approximately between May and August so we are right in the middle of the season. Now we are observing an emergence almost every morning. Although they nest all over the island, the vast majority of nests are occurring on the West Coast along Bois Blanc (the beach on the hotel side). Just past Chalet 14 we have had 3 nests laid almost on top of each other; these have occurred at 2-3 week intervals which has led me to believe it could be same female returning to a favoured spot to lay her nests.  Every time a nest is laid we place a pole with a coconut stating the species, laid date, due date and estimated number of eggs in the nest. Every time this particular female emerges she bundles over the pole from the previous nest and appears to crawl all along the edge of the vegetation looking for the perfect spot to nest. It is a struggle to decipher the unruly mess she’s made, particularly when it’s around 7 in the morning and there are turtle tracks in every direction.

Finally the end of May marked the arrival of the sooty terns (Onychoprion fuscatus), many individuals are currently breeding on nearby Bird Island and there are still many sooties flying around Denis. Preparing the field for the arrival of the sooty terns began as early as February. Sooty terns require an open field to breed, and therefore we cleared rocks, pulled weeds and allowed the cows to graze before putting the plastic model birds and speakers in place. These are placed in the field to attract sooty terns that are flying over, possibly in search for a breeding spot. After 4 months of work I was over the moon just to see the birds arriving on the island and getting the opportunity to see some up close.  Over a couple days in early June, we saw close to 100 birds landing amongst the plastic models on the field around South point which we have cleared for them. Earlier this week, Martijn saw one individual attempt to mate with one of the models, and one of the guests who was with him on island tour managed to take a photo! Sadly this is the closest we have come this season to having a breeding population on Denis. It is very possible we are now past the timing to start a colony and we will have to wait till next year, given eggs are already being laid on Bird Island.

Sooty terns landing amongst the plastic models

Sooty terns in flight

We will continue to carry out observations at the sooty tern site; we can still see many flying over or circling the cleared area. You would think that on days with limited success it could be easy to be disheartened, this is definitely not the case. By spending even just one hour on the observation platform you will see the vast array of birds Denis Island has to offer, which after 5 months is still truly remarkable. From a few blue pigeons flying low across the field calling at the top of their voice to a Magpie Robin inquisitively hopping around in front of you, every interaction is special. If you’re very lucky you will even see a flight of Great Frigate Birds gliding effortlessly above the cacophony below. These incredible birds can have a wingspan over 2 metres and still only weigh around 1 kilogram; they are quickly becoming a personal favourite of mine.  

As I enter my last month of Denis Island, I am trying my best to take in every single moment. Sights I now see as normal will soon be an astonishing memory. The likes of passing Aldabra Giant Tortoises on the way to work or watching White-tailed Tropic Birds flying overhead as I’m sunbathing are unique moments that almost everyone would love to experience. Even though I am very exciting to return home and see my family and friends, I will definitely miss my time on Denis Island.

By: Nick Burnham