Manx Shearwaters
Early records of Shearwaters on Copeland
The first recorded visit to Lighthouse Island by ornithologists was in 1939. Renowned Northern Irish ornithologist C Douglas (Jimmy) Deane stayed overnight and observed shearwaters landing in the sub-colony areas presently designated ‘Cliff’ and ‘Alley’. He also dug out one burrow to find an adult incubating an egg. At the time this was considered the proper way of proving breeding.
A group of four servicemen, including the late Ken Williamson, carried out a survey of breeding species in June 1941, although concentrating on terns, they recorded that Manx Shearwaters were present at night.
Another local ornithologist called Arnold Benington brought out an adult education group to the island in 1952 to investigate the possibility of establishing a bird observatory in the style of Skokholm and to ring Manx Shearwaters if possible. A total of 42 were ringed. This formed the beginning of the Copeland study. Some of these birds might still be alive.
Speculation about how long shearwaters have been breeding on Copeland tends to conclude that the colony is relatively new. Documentation of the Island’s history is sparse and little detail is available. It seems that farming was carried out during hundreds of years of occupation by monks from Bangor Abbey until the 17th century. Then the lighthouse was established. It was operated by two families whose pay is said to have been so poor that they were allowed to farm the island in lieu of pay. The lighthouse ceased to operate in 1884 when a modern one was built on neighbouring Mew Island.
The whole island is covered in the remains of cultivation in the form of derelict lazy beds. This Irish term refers to inconspicuous, gently undulating ridges and trenches, vegetated in semi-natural sward. They were created by a method of cultivation, using a spade, which worked the soil easily and improved drainage in the famously wet climate.
Local folklore suggests that the island was not depopulated until 1920. At some stage rabbits, Oryctolagus cuniculus were introduced. It is reasonable to assume that this happened after 1884. In other colonies, it has been reported that shearwaters dig their own burrows but this has never been observed on Copeland where we believe they only use existing rabbit burrows. Shearwaters could not have bred on Copeland until rabbits had created a surplus of burrows.
It seems, therefore, that the colony has risen from zero to almost 3,000 pairs in approximately 100 years.
Origins of the Copeland birds
If the Copeland colony is little more than 100 years old, it is possible that the origin of the colonisers might be identified by genetic testing. In 1977, in the days before DNA ‘fingerprinting’, David Whitehouse, accompanied by David Parkin, visited Copeland to sample blood plasma proteins. One hundred and twenty birds with retrap histories and known to be of breeding age were sampled. The analysis was made by protein electrophoresis. They were investigating the balance of polymorphism in a group of proteins involved in the immune response system. The results indicated that the balance of polymorphism for Copeland birds was distinctive and not similar to that of Skokholm or Skomer birds. These two colonies are unlikely to have contributed many birds to the developing Copeland colony.
Influences on the shearwater population
The waters of the North Channel seem to be ideal feeding grounds for shearwaters. Typically, several feeding rafts of around 1,000 birds would be reported by local fishermen within 10 km of Copeland. Similar sightings are made from cross-channel ferries. It seems reasonable to assume that a much greater population could be supported in the region. There has always been a shortage of breeding sites in the North Channel area. There are few islands with the right terrain. Sanda at the south end of the Mull of Kintyre was thought to have had a colony of around 100 pairs. It became severely threatened when predatory mink, Lutreola lutreola, arrived, but these were removed and the colony still exists.
Regarding the population on Copeland, the weather and food availability are obvious (offshore) factors in the success of local populations. On land, at the colony, the population levels are influenced by:
- the availability of burrows;
- the humidity of the soil in the burrows;
- flash flooding;
- the level of predation by gulls Larus spp., Otters Lutra lutra, and mink.
It now seems that, with a burrow occupancy of 55% (see below), there are still many available nesting burrows. However, there is a possibility that rising numbers of shearwaters could cause downward pressure on the rabbit population. It is obvious that rabbit densities on Lighthouse Island are very much lower than on Big Copeland Island, approximately 2km away, or on Skomer and Skokholm. If rabbits are unable to dig enough new burrows to sustain their own population and cater for the rising shearwater population, the increase will stop.
There are indications that productivity is lower than average in wet years. It has also been noted that, when burrows are flooded, eggs are chilled and young are forced out onto the ground surface.
Influences on the rabbit population
There is no obvious evidence why the rabbit population is so low on Copeland. Visual comparison with the other three islands mentioned indicates a greater lushness of plant growth on our island, though there are surprising similarities in the plant cover. Perhaps past management has favoured ragwort (Senecio jacobea) too much. It is a useful food plant for autumn migrants. It is not eaten by caterpillars of the Cinnabar Moth (Tyria jacobeaea) on Copeland. Rabbits are probably cumulatively poisoned by it like other herbivores. It may be having a further suppressing effect on top of the normal epidemics of viral haemorrhagic disease, myxomatosis and trematode infestations, which presumably are no worse on Copeland than elsewhere.
The rabbit interaction with vegetation is an interesting one. At high population densities, rabbits maintain a sub-climax vegetation of cropped marine grassland. During dips in population, rabbits lose control of parts of the sward, which then overgrow into rampant rabbit-resistant vegetation. On Copeland, the species involved are Bracken (Pteridiun aquilinum), Hogweed (Heracleum sphondiliun), various thistles (Cirsium and Carduus spp), Nettle (Urtica dioica), Red Campion (Silene dioica), and, worst of all, the alien Himalayan Balsam (Impatiens grandiflora). In the absence of other intervention, the rabbits seem unable to reclaim these areas even when their population recovers. The rabbits progressively lost ground until the early 1980s when mowing started, causing the trend to be stopped and even slightly reversed, at least in places. Experimentation on mowing regimes is still continuing. If the ground vegetation continued towards scrub, the shearwater population would eventually dwindle.
Habitat management for the shearwater colony
As already mentioned, mowing is progressively opening up densely vegetated areas of the colony and returning such areas to the short sward that they were in the 1950s. There has been a decision to try mechanical rather than chemical control for some more years. This policy may have to be reversed in the light of experience. It is worth noting that vegetation control has advantages both for ringer accessibility and for the shearwaters themselves. Observing that birds departing from the colony use paths that have been maintained by human trampling, the technique of creating runways to aid the shearwaters’ take-off has been tried and judged very successful. Such runways on Copeland have been made to run WSW towards the glow of artificial light from Bangor, County Down and Belfast, and ENE towards the lighthouse on Mew Island about 500 m away.
Burrow Availability
It has been estimated that 55% of the burrows on Copeland are occupied by Manx Shearwaters (John Stewart and Kerry Leonard, pers. comm. Seabird 2000 survey, see also table below). Concerns about the rabbit population may be premature but it seems that in future there may be a problem if the rabbits continue to fare badly. Hence the mowing programme should benefit the rabbit population as much as the shearwater population. On Copeland the maxim is ‘No rabbits – no Shearwaters’.
Observations of flighting
Due to the light from nearby towns and city to the west and south-west, it is possible to watch the birds flighting over the colony. Like Storm Petrels (Hydrobates pelagicus), the shearwaters prefer to approach their burrows flying into the wind. They are much less likely to do this if the nest site is close to the sea and/or on high ground with a clear aspect overlooking the sea. Brooke (1990) suggests that an upwind approach to the burrow will minimise ground-speed on touchdown.
The height at which they generally fly is remarkably low at about 1 metre or even less.
Dives from great height, often in pairs, only levelling out barely above the ground have also been seen. Fast flying birds have been observed to rise upwards in a circular sweep and even sometimes ‘looping the loop’.
The most usual approach to the colony involves flying in along a preferred flightline, often twisting and turning, failing to land and repeating the circuit several times before eventually landing at the chosen spot. This repeat flighting along identical flightpaths is indulged in both by silent breeders and by noisy adolescents. While catchers are using the lying-in-wait method of catching, they are always impressed by how adults can land exactly at the entrance of their burrow. This is so accurately done that quite often such birds escape capture because they go down their burrow so quickly.
Evolution of the Shearwater study on Copeland
At first, only simple ringing was done, i.e., no biometrics or site information were recorded. The chances of recording life histories were reduced by the use of the soft aluminium ring known as DE (double-ended). Many birds required to be re-ringed every 4 years to avoid ring loss. Its use was phased out in 1963, when it was replaced by monel rings. This alloy was stronger, but contact with salt water caused pitting and severe corrosion, meaning that they did not last much beyond 10 years. By the early 1970s, a better alloy called incoloy was introduced which was the perfect ring for shearwaters. Later it was replaced by stainless steel rings which had almost identical properties. After DE rings, we tried the ‘Feo’ monel rings for a while but found they were more difficult to fit, especially for those who did not ring many shearwaters. At some stage Copeland switched to E rings and heretically (at the time) put them on round. While it might be argued that it would be slightly tight on a small percentage of the birds, it was found that this was not a problem because the back of the tarsus is soft. The biggest advantage of the round ring is that wear is shared equally all round the ring. After almost 30 years, it has not been necessary to re-ring any birds ringed with an E incoloy or E stainless steel ring. Not only is there no sign of wear but there has been no sign of any inconvenience to the shearwaters. A final good reason for using the E ring was that it was easy to fit, again important for amateur ringers.
Our records are kept in four volumes of old-fashioned ledger books. These are kept on the Island during the year and filled in by the ringers the day after the handlings are made. At night the ringers are aided by a scribe, who records all details on a purpose-made field sheet or in a waterproof notebook. When the field sheets reach the mainland, the Records Secretary also makes a paper copy of the data. Two other members are working on computerising the data.
Catching techniques
We intend to do more work on the effect of catching technique on the age profile of the catch. A preliminary experiment in 1993 showed that 42 retraps caught by ‘hunting’ had a mean age of 8 years, while another 42 caught by ‘lying-in-wait’ had a mean age of 15 years. If this turns out to be substantiated, it has interesting implications on how catching should be conducted. During the ringing course in 2001, four different catching techniques were used. We await the results of the analysis with some interest.
The pullus ringing effort
Particularly since 1973, a considerable effort has been made to ring pulli. The following table shows the annual pullus totals.
It is difficult to draw clear conclusions from the raw data. Variations in the totals are due to:
- variable manning through the fledging period (in some years up to five nights have gone unmanned);
- minor variations in skill level (but persistence is a more variable factor which is difficult to legislate for volunteers!);
- weather patterns during the season which can influence productivity (weather during the fledging season can influence the enthusiasm of the ringers);
- food supply may be a factor influencing productivity in some years.
| Year | Ringed | Year | Ringed | Year | Ringed |
| 1952 | 0 | 1969 | 35 | 1986 | 431 |
| 1953 | 0 | 1970 | 108 | 1987 | 460 |
| 1954 | 38 | 1971 | 103 | 1988 | 401 |
| 1955 | 12 | 1972 | 163 | 1989 | 549 |
| 1956 | 95 | 1973 | 262 | 1990 | 362 |
| 1957 | 56 | 1974 | 241 | 1991 | 483 |
| 1958 | 69 | 1975 | 266 | 1992 | 549 |
| 1959 | 108 | 1976 | 245 | 1993 | 263 |
| 1960 | 33 | 1977 | 316 | 1994 | 626 |
| 1961 | 85 | 1978 | 345 | 1995 | 682 |
| 1962 | 110 | 1979 | 246 | 1996 | 711 |
| 1963 | 85 | 1980 | 249 | 1997 | 655 |
| 1964 | 64 | 1981 | 337 | 1998 | 314 |
| 1965 | 97 | 1982 | 191 | 1999 | 350 |
| 1966 | 74 | 1983 | 332 | 2000 | 450 |
| 1967 | 67 | 1984 | 431 | 2001 | |
| 1968 | 31 | 1985 | 428 | 2002 |
Table showing number of Shearwater pulli ringed each year
Foreign recoveries
Twenty nine of the overseas recoveries have followed the big figure-of-eight migration route that is now generally accepted (I hope!). They include 1 from Spain, 17 from Brazil, 2 from Uruguay, 4 from Argentina, 1 from South Africa, 1 from Angola, 1 from the USA (Florida) and two from Canada.
Interestingly, only one of the Brazilian recoveries involved a bird that survived as long as 6 years and therefore was old enough to be a breeder, so Copeland recoveries have not been able to shed any light on where adult mortality occurs other than many summer recoveries, mostly within 200 km of the colony.
Analysis of recoveries is best done using all British data so no further comments are presented here. However, there have been three, somewhat atypical recoveries, that are worthy of mention.
Two were freshly fledged birds to Denmark and Switzerland. They follow the pattern of some other birds on their first flight which have been recovered over many locations in Britain and Ireland, but which did not go so far. Such birds are clearly lost and probably storm blown. Some are released and eventually reappear on Copeland to breed. One was a lighthouse strike and was released, though described as sick, and was back on the Island three years later. A similar story concerned a bird which became grounded in the centre of Belfast over 30 km away. It was picked up by a shipyard fitter on his way to night shift at 2130 hrs GMT and taken to the docks where it was thrown in the sea from the gangplank. Three years later, it was back prospecting on Copeland.
The Copeland Bookings Secretary has often been contacted by telephone about birds stranded under street lights in September. Of about 12 birds examined over many years, the opinion of the public that the bird was sick or injured has always proved to be wrong. The birds have only been stranded. Releasing at sea is their only hope. If released from a height or even thrown out to sea, all these birds readily fly. Taking lost birds into care usually leads to their demise.
The recovery of a Copeland shearwater from the shore of Lake Huron, Michigan, U.S.A. on 19th August 2000 was interesting for several reasons. It was ringed on 7th September 1991 and had not been handled on Copeland thereafter. Perhaps it had made a reverse direction migration.
Interesting retrap histories
There are a number of distinctive patterns of retrappings that have been identified on Copeland. Whether a bird is retrapped or not and how frequently is influenced by 4 factors.
- It is less likely to be retrapped in the northern sub-colonies which are avoided by some ringers and generally less frequently visited by all ringers.
- If the burrow is near to a path or open area, the adults will present themselves for recapture more frequently. Some are caught very regularly because they are nesting under the path.
- A clear take-off flightline will allow a bird to avoid recapture.
- Some individuals, perhaps most, will, with increasing age and experience, become adept at avoiding recapture.
Retrap patterns of birds ringed as adults (Euring age code 4)
- Many birds are never recaptured (45%).
- Some are frequently retrapped during the same or next one or two seasons (prospecting birds), followed by long retrapping intervals (breeding birds). The majority of newly ringed adults are in this category.
- Some birds are infrequently retrapped over many years (already breeding when ringed)
- Types 2 and 3 sometimes show a burst of frequent retrappings over 1 to 3 seasons. This can be interpreted as the bird having lost its mate and returning to courting/prospecting behaviour.
- For some birds there is a very long interval between ringing and first (or only) retrapping (10 or more years), indicating that the bird was any or all of the following: off the beaten track; adept at avoiding capture; or, nesting at an easy take-off site.
Birds ringed as pulli
- No retrap history (89%). Birds could have died between fledging and the age they would normally return to the colony, or could have transferred to another colony.
- Retrappings begin in years 3 to 5 with several handlings followed by retrappings at long intervals, i.e. following adult type 2 pattern.
- Some birds showing pulli type 2 behaviour can be followed by adult type 4 pattern.
- A tiny number of pulli show adult type 5 pattern.