Ascension : Conservation Weekly
Submitted by The Islander (Conservation Office) 20.03.2008 (Article Archived on 03.04.2008)

The Army Ornithological Society (AOS) mounted their 14th expedition to Ascension from 7-20 Feb 2008.

Army Ornithological Society expedition to Ascension

By Andrew Bray

The Army Ornithological Society (AOS) mounted their 14th expedition to Ascension from 7-20 Feb 2008.  The aims of the expedition were to collect data on population changes of bird species, monitor predation and identify threats to the seabirds on Ascension.  As ever the expedition concentrated on the Sooty Terns.  In addition, a census of White Terns was carried out across the Island including the cliffs of Boatswain Bird Island.  The results of this census have yet to be evaluated however, the initial results look like there is a stable population using various sites around the Island.  It was also very noticeable during our travels that the Brown Noddies were now nesting on the mainland near the stacks that they previously nested on.  This is a major result for the conservation plan and a joy to behold.

This trip it was estimated that there were 175,000 pairs of Sooty Terns on the two fairs.  This is less than previous seasons but was not unexpected and definitely no cause for any alarm.  The main difference to previous visits was that there were 17 sub fairs compared to 6 or 7 in the past.  The birds were spread out across the fairs and the quadrat surveys confirmed that the density per 10 square metres had reduced.  This again demonstrates the success of the conservation plan as the birds no longer feel threatened.  They are still susceptible to various types of predation by mynas, rats and frigate birds and various surveys were carried out to quantify this.  On this trip a huge effort was put into finding previously ringed birds in addition to ringing another 2,000 adult birds.  There were 350 re-traps that were all previously ringed on Ascension up to 10 years ago.  This is the way that we can estimate adult and juvenile survival rates.  On the Waterside fair there were large areas of deserted eggs and as we left a new sub-colony was bedding itself in at Mars Bay.  We assume that these were the birds that had deserted their eggs earlier and were about to try again; it takes 21 days for an egg to form in the female.  During our time on the island we were able to assist members of the Conservation Team and visitors from the RSPB with some training in the field techniques used. 

The expedition has a small plea to make and that is to obey the signs at Mars Bay.  We witnessed an attempt by some locals to drive through the nesting birds that covered the track.  We were able to stop them but only after they had caused some destruction.  Though we concentrated on sea birds we did take some interest in the mynas around the rubbish dump as they are breeding there.  There is a sizeable population of over 300 birds.  This may be something that we might look at in the future.  During the visit we were able to test the formula recently printed in the Journal of Zoology on how to sex birds in the field.  All the research for this paper was based on our work on Ascension but has applicability to all Sooty Tern colonies around the world.  It is likely a full report will appear in that journal on the success; suffice to say that the probability of determining male or female matched the expected results.

The expedition had an eventful trip enlivened by some major use of the airfield which required us to modify our plans on a few occasions.  We would like to thank the RAF for hosting us at what was a very busy time especially for dovetailing us in around periods of operational activity.  Finally the expedition would like to thank the Conservation Office for their assistance in providing us with information and help in getting tasks completed.  We are aiming to return in December 2008.