Inishglora expedition 2006

The Copeland Bird Observatory has been organising visits to Inishglora since 1958 to ring Storm Petrels. The ringing work has been followed up by recording retraps in successive visits and therefore collecting data suitable for population and survival analysis. The visits made in 1965, 66, 74, 75, 76, 77, 80, 86, 97, have resulted in a very large data set of retraps being accumulated which will be analysed along with the results of the visits being undertaken in 2006 and 2007. Proper analysis of the earlier work has only become possible with the advent of sophisticated computer programs in very recent times. It is intended that the analytical work will start in the autumn of 2007. To date, almost 28 000 Storm Petrels have been ringed.

The study is not just a simple ringing study. The data has been collected in such a way that a variety of population analyses and estimations will be possible. Some preliminary analyses have been done.  It also involves a detailed recording of the variability of brood patches during the breeding season and the usefulness of this in correcting calculations of colony size. The study involves a comparison of brood patches, retrap rates and control rates at three contrasting ringing sites. These are the big colony on Inishglora in Co Mayo, a small colony on Roaninish in Co Donegal, and the non-colony catching site on the observatory itself in Co Down. The purpose of the work is to develop a method of establishing the size of any breeding colony.  Mark-recapture techniques will provide useful evidence to compare with results from tape-playback survey methods used for all the British and Irish colonies as part of the Seabird 2000 breeding seabird count.

The plan was to continue the long term study of Inishglora by visiting in August 2006 for a minimum of 3 ringing nights and to follow this with a repeat visit in 2007 to sample for the number of ringed recaptures from 2006).  We suspect the tape-playback method may have underestimated the colony size on Inishglora and potentially at all the other colonies in boulder beaches. We will also be able to look at the declining retrap rates from all the previous expeditions. This provides several mathematical opportunities for calculating survival rates. We have evidence from previous visits suggesting that there is a much larger population on Inishglora than was reported for Seabird 2000.  Of course it is also possible that the population has declined since our last visit. It was hoped in advance of the visit that we would handle 3000-4000 birds on the 2006 trip.

There is a second line of research, which involves the brood patch study, which has underlain the Copeland study of Storm Petrels over the last 30 years. Variable numbers of non-breeding birds are present at colonies and confuse any attempt at population estimation by any of the usual mathematical methods based on the Lincoln Index (or “mark/recapture analysis”). For over 30 years now, the details of the state of the brood patches of Storm Petrels on Copeland, where all the birds are known to be non-breeders, have been recorded for comparison with the brood patches of birds trapped on colonies where most of the birds would obviously be breeders. By comparing the differing conditions of the brood patches at colonies and non-breeding sites, it will be possible to calculate the proportion of non-breeders in a catch and thereby correct for the problem in mark/recapture analysis. It is already clear that the proportion of non-breeders to breeders is actually constant for any one colony in mid August. Indeed each colony has its own ratio.  This has already been shown to be related to colony size. In general, the proportion of non-breeders in the catch becomes lower with increasing colony size. This ratio alone can give a quick guide (in terms of order) to the colony size.

The benefits of this study will be that the development of a mathematical method of estimating colony size will also allow populations to be monitored, an essential pre-requisite for developing a conservation strategy. The results will be applicable across the whole of the Storm Petrel’s range (which is the NE Atlantic) and are likely to be applicable to nocturnal petrels worldwide.

What happened

The planning for the expedition took several months. It was intended to stay from the 12th to the 17th August. In the event, we returned on the 16th in the correct anticipation of continuing fresh to strong NNW winds. Packing all the required kit took a week. Fourteen Copelanders took part. All were well kitted out. Surplus food was taken in case of marooning. Nearly all of the previous visitors had experienced bad weather and this trip was no exception. Everyone had been well prepared to cope with the likely conditions. Camping on an uninhabited Atlantic Island is not easy and could be something of a survival challenge.

In the event, the 2006 expedition experienced only one good night (the second night) of calm conditions which allowed the catching of 1000 Storm Petrels. The first night was rainy and windy. After a long and difficult journey out, it was something of a relief for everyone that it was too windy so we went to bed early. The third and fourth nights also degenerated into wind and rain by around 2am, cutting short the working night which usually would last until 5am.

Nevertheless, the expedition was enjoyed greatly by the participants, many of whom had been before. This was despite only about 2000 birds being handled, including retraps and controls. With continuing bad forecasts, we came off a day early, and this turned out to be the right decision as the wind backed into a worse direction.

A total of 1861 new Storm Petrels were ringed. We processed 69 retraps from previous visits to Inishglora and also 29 controls from elsewhere. We handled a total of 1959 Storm Petrels, and 2 Leach’s Storm Petrels.

If the wind had not blown fresh to strong from the north for much of the time, and it hadn’t rained, we could easily have reached 4000 on 4 good nights, as we did in 1986, but it was not to be, this year.

Summary of retraps:

We caught one from 1975 (31 years ringed, one year short of the BTO record).

One from 1977 (29yrs)

Three from 1980 (26yrs)

Ten from 1986 (20yrs)

Fifty-four from 1997 (9yrs)

Controls:

Two foreign – Portugal (from 22.05.98), and Norway. See: http://stormies-online.blogspot.com/

27 birds with BTO rings. We already know that about 6 of these birds were originally ringed at Tullagh, Co. Donegal by one of our members, Boyd Bryce, in the last couple of summers and 3 were from nearby Annagh Head, only about 2km north of Inishglora where another of our members, Declan Clarke, ringed about 500 during the weekend before the Inishglora trip. He ringed over 500 more on the following weekend and caught 4 of the Inishglora birds. These numbers of movements between such close places may seem low, but they are actually no surprise to us. Breeding birds don’t wander, only the adolescents. A couple of others were ringed on Duvillaun More, about 10km south, over the last few summers. Four were ringed by Declan Manley in 2004 or 2005 at Portacloy and Kid Island in North Mayo. We will have to wait until we hear from the BTO about where all the others were ringed originally.

Interesting retraps:

 Only one bird was handled for the third time. There were quite a lot of these up to 1986. They are useful for calculating colony size.

2352105 ringed 11.08.86, retrapped 16.08.97 and 14.08.06

Here is a table of the numbers ringed on all the visits to Inishglora in the past:

Year	1965	1966	1974	1975	1976	1977	1980	1986	1997	2006
Ringed	500	2243	1909	2934	3324	2717	1869	3973	3150	1959

This 2006 expedition is therefore the 7th best one for numbers ringed or the 3rd worst one! Given the conditions, we actually did well.

Here is a website which might be of interest: http://homepage.tinet.ie/~caoim/oileain/glora.html

(We didn’t drink from the well!)

A search with Google should find more.

There will be a lot more about the trip in the Annual Report for 2006, due early spring 2007, available to non-members by post.

Inishglora (Inis Gloire) Photogallery