[Viv Booth updates us on her work with the Ascension Island Government Conservation Department]
Three weeks on Ascension Island and I’ve seen my first sooty tern at last! When I arrived, I was disappointed to learn that the terns had departed just days before. Five key species are monitored here: Ascension frigatebird, masked booby, brown booby, sooty tern and brown noddy, and although their breeding isn’t synchronised and some of them can breed at any time, things were looking quiet on all the colonies at the start of August.
The seabird monitoring work continued of course. With Nathan Fowler, from the Ascension Seabird Project, I visited some of the colony sites to count the handful of active nests and monitor the progress of their chicks. We collected the nest markers from empty sites. We also started to walk some stretches of the coastline in the hope of finding new breeding areas – something there just isn’t time to do in peak season.
The Ascension coast is spectacular: tremendously craggy and very varied. At ‘The Inkpot’, the boulders of black, bubble-filled volcanic rock look freshly spilled. At Whale Point the rock is granular and grey, but formed into contorted shapes which could grace any gallery of modern art. Eroded edges reveal the layers of subtly-shaded solidified ash at Hummock Point. This coast is carved by ferocious waves, which have built up their swell over thousands of miles of open ocean, creating caves, arches, stacks and inlets.
The view landward from Letterbox (Viv Booth)
There are beaches too: look at the dark volcanic sand in Crystal Bay and you will see that it sparkles with tiny fragments of semi-precious stone, and in the sheltered coves, white coral sand accumulates, in stunning contrast with the surrounding black rocks. Here the sea is deceptively tranquil and gleams a tropical turquoise.
In the middle of the month, there was the first hint that some birds might be thinking of returning. A few masked boobies stood around in pairs, honking (females) and whistling (males). One day, the single big brown booby chick at the Northwest Point colony was accompanied by around 150 brown noddies circling and skimming the waves.
A masked booby pair (Viv Booth)
Then suddenly the sooty terns were back at Waterside - where none had been the week before, now thousands of birds were swooping and calling, hovering low over us as we intruded briefly into the colony to check if any eggs had been laid. The guano-stained rocks under our feet were mirrored by the monochrome mass of birds above us.
The breeding cycle of sooty terns here is on average 9.6 months. That figure encompasses an awful lot of variability though, and the cycle and the success of the breeding attempts is highly dependent on food availability. A sub-annual cycle makes sense in a lot of ways – seasons don’t vary much this close to the Equator. Flexibility in response to food availability means more opportunities to breed, so hopefully more chicks fledged, plus any predators which are stuck in an annual rut can be more easily avoided.
Birds returning so soon might have failed in the last breeding attempt. There were some signs last month that some chicks were underweight, and more than the usual number of older chicks didn’t quite make it through to fledging. This might suggest a temporary lack of food, and birds returning now indicate that the lean period is over and they are back for another go. We wish them every success this time round.
Sooty terns wheel above (Viv Booth)