Skomer Research Articles

A survey of Cryptosporidium species in Skomer bank voles (Clethrionomys glareolus skomerensis)

AbstractA survey of Skomer voles (Clethrionomys glareolus skomerensis) conducted in August of 1994 and 1995 discovered that 51% of live‐trapped animals were positive for Cryptosporidium species (Coccidia). Of the positive animals, 85% were shedding C. muris in their faeces, 5%C. parvum and 10% apparently both parasite species. On the U.K. mainland, the prevalence of Cryptosporidium in the bank vole (Clethrionomys glareolus) is a quarter of that on Skomer and the species normally found is C. parvum. Interest in C. parvum stems from the often severe diarrhoeal disease cryptosporidiosis which it can cause in humans and livestock. The parasite occupies the gastro‐intestinal tract and is transmitted between hosts by the faecal‐oral route. It has been suggested that wild rodents may be an important reservoir of infection by C. parvum for livestock. However, on Skomer island, C. muris, which is rarely found in livestock, is the dominant species infecting voles.

Lichens of Skomer Island, West Wales

Skomer Island, a National Nature Reserve, lies off the West coast of Wales. This small island holds lichen communities of international importance associated with large populations of seabirds. Saxicolous lichen communities are described, 248 species listed and details given of a base-line monitoring programme, which will provide data on changes in the lichen flora over time and distinguish cyclical from permanent deleterious changes. Threats to island populations are discussed, such as the likely effects of oil pollution following the Sea Empress accident in February 1996.

LICHENS OF SKOMER ISLAND, WEST WALES

Skomer Island, a National Nature Reserve, lies off the West coast of Wales. This small island holds lichen communities of international importance associated with large populations of seabirds. Saxicolous lichen communities are described, 248 species listed and details given of a base-line monitoring programme, which will provide data on changes in the lichen flora over time and distinguish cyclical from permanent deleterious changes. Threats to island populations are discussed, such as the likely effects of oil pollution following the Sea Empress accident in February 1996.

Hematology of fledgling Manx shearwaters (Puffinus puffinus) with and without 'puffinosis'.

Hematological parameters were measured in 14 fledgling Manx shearwaters (Puffinus puffinus), with the disease puffinosis and in 10 birds that did not have the disease, on the Island of Skomer between 2 and 11 September 1991. The mean plasma fibrinogen concentration was significantly higher in the diseased birds and some of these had abnormally elevated monocyte counts. No other significant differences were observed.

An Experimental Study of the Effects of Timing of Breeding on the Reproductive Success of Common Guillemots (Uria aalge)

SUMMARY (1) The reproductive success of 474-574 pairs of common guillemots was studied from 1985 to 1987 on Skomer Island, Wales. (2) Laying was highly synchronized, and within years productivity decreased seasonally from shortly after the period of peak laying. (3) The timing of breeding of one group of forty-five pairs was experimentally delayed by 13 days to test whether timing of breeding relative to calendar date or relative to other pairs was the factor causing the seasonal decline in productivity. The results showed that timing relative to other individuals rather than calendar date was important. (4) Naturally late breeders provisioned chicks at a lower rate than early breeders, but there was no evidence for a seasonal deterioration in food availability. (5) The effects of physical characteristics, breeding density and synchrony on productivity were examined in a logistic regression analysis for 567 breeding sites. Only density and synchrony had significant effects. Productivity increased with density and decreased for late breeders. (6) Predation was the main cause of breeding failure. High-density breeding reduced vulnerability to predators. Synchrony was important for the benefits of highdensity breeding to apply throughout the breeding period, and also for swamping predators.

Experimental Evidence for Food Limitation of Egg Production in Gulls

Lesser Black-backed Gulls Larus fuscus nesting on Flat Holm Island in 1989 laid significantly smaller clutches than birds nesting in the same colony in the years 1983-86. Provisioning territories with supplementary food (fish) in 1989 during the prelaying period significantly increased clutch size and egg size compared with unfed controls. Similar experiments carried out on nearby Skomer Island in 1988, where egg production by unfed birds was typical of the species in Britain, did not increase clutch or egg size. The results clearly indicate that egg production can be limited by poor food supply during the laying period, but suggest that such food limitation is not a proximate mechanism for the restriction of the normal clutch to three.

Frequency of isolation of campylobacter spp., Yersinia spp. and salmonella spp. from small mammals from two sites in Southern Britain.

Small wild mammals were trapped at two sites in the United Kingdom: Skomer Island, Dyfed and a farm in Dorset. Faecal samples were collected from 43 rodents of two species on Skomer and tested for the presence of Yersinia. Samples of faeces and of material from the terminal ileum were collected from 141 animals of eight species in Dorset and tested for Campylobacter, Yersinia and Salmonella. In addition some samples of spleens from the Dorset animals were tested for Campylobacter. Four typable isolates of Campylobacter were obtained from the Dorset site, two from spleens from shrews and two from intestinal contents from a bank vole. Nineteen isolations of Yersinia were made from the Skomer animals and seventeen from animals in Dorset. No isolations of Salmonella were made from any of the animals sampled.

Precociously developing individuals in populations of chickweed [Stellaria media (L.) Vill.] from different habitat types, with special reference to the effects of weed control measures

summaryLong‐term weed control in gardens and arable areas is likely to be a potent selective force favouring precocious development of annual weed species. In an experiment with Stellaria media (L.) Vill., we grew progenies from open‐pollinated seed of a number of seed‐parents collected from 12 British populations of five habitat types. We raised plants in a temperate glasshouse and a garden plot, to see if plants from areas subject to weed control ‐gardens and arable fields – had a quicker rate of development from germination to flowering and fruiting than plants from habitats subject to less weed control (waysides) or no weeding pressure (seasonally exposed river sediments and bird colonies).Comparison of the behaviour of plants in the glasshouse and out‐of‐doors revealed a broadly similar pattern of behaviour. However, for some, but not all seed‐parents, rate of development was different in the two sets of conditions.In conformity with hypothesis, plants from one of the gardens were quick to reproduce, but plants from Ness Botanic Garden and arable fields were more variable than expected. Plants from less well weeded and non‐weeded sites did not conform to expectation. Plants from waysides were quick to reproduce, so too was much of the material from a bird colony on the island of Skomer. While some late‐developing plants were detected from a second bird colony (Fame) and from exposed river sediments by the Tweed and Manifold, we found a small number of precocious and some intermediate individuals in the progeny of some seed‐parents.It is possible that bird colonies and exposed river sediments are heterogeneous habitats, in which there are niches where ‘native’ variants with different rates of development are at a selective advantage.However, there is another explanation of our results. First, we discovered that, while some of the seed‐parents were probably behaving as homogeneous lines for rate of development, others show ed segregation, providing evidence that a degree of outcrossing is possible in populations of Stellaria. Secondly, there is evidence that human activities have led to habitat disturbance in and around the bird colonies and riverside vegetation we have studied. Our findings are consistent with the hypothesis that, gene flow by pollen and/or seed of precocious weedy plants has occurred in these man‐disturbed sites, leading to different patterns of variation involving hybridization between ‘introduced’ precocious plants and ‘native’ slow‐developing variants.

Population Dynamics of Common Guillemots Uria aalge on Skomer Island, Wales

The Common Guillemot population on Skomer Island, Wales, has recently increased following a long period of decline. We measured population parameters in 1985-89 and compared them with parameters measured in 1973-75 to identify the processes responsible for these population changes. Productivity increased significantly from 0.72 chicks pair-1 yr-' in 1973-75 to 0.79 chicks pair-1 yr-' in 1986-87. Adult survival was higher in 1986-89 (94.0%) than in 1973-75 (91.5%), but the difference was not significant. Information is not yet available to determine whether survival to breeding age, and therefore recruitment, has also increased. A model of population growth is presented, incorporating observed changes in productivity and adult survival, and employing three values for survival to breeding. A close fit to observed population changes was obtained with a survival rate to first breeding at five years of 41.1%, the highest survival rate previously recorded for Common Guillemots.

Intraspecific variation in egg composition and yolk formation in the common guillemot (Uria aalge)

Common guillemot eggs were collected and analysed in two years on Skomer Island, Wales, to investigate the effects of environmental conditons during the pre‐laying period on egg formation and composition. Pre‐laying attendance at breeding colonies indicated more favourable environmental conditions in 1987 than in 1986. The size of eggs did not differ between years, but eggs were laid earlier in 1987 and the time taken for yolk deposition was also shorter in 1987. Two distinct effects of environmental conditons on yolk formation were indicated: first, on the timing of initiation of yolk deposition; and secondly, on the duration of the yolk deposition period. Egg composition also differed significantly between years with a higher proportion of albumen and a higher proportion of lipid and non‐lipid solids in yolks in 1987. These results are discussed with respect to environmental conditions and the constraints on egg production.

Extreme chromosomal heterogeneity in a small-island population of Rumex acetosa

Chromosome analyses of 227 mature plants of the dioecious species Rumex acetosa collected on the small island of Skomer have revealed an extremely high level of unique and polymorphic variation. The three common polymorphisms in this species--supernumerary segments on chromosomes 1 and 6, and B-chromosomes--are widespread on the island and the frequency of supernumerary segment 1 is higher than in all 37 mainland populations previously studied. Novel variants, unknown elsewhere, occur in each polymorphism. Fourteen different chromosome rearrangements are unique to the island, and eleven of these were detected in 67 plants from a small area which had undergone a population crash in 1977. It is argued that the genome of R. acetosa is undergoing rapid reorganisation on this small island which may be associated with an enforced shift towards inbreeding in this dioecious species.

Late-orogenic alkaline/subalkaline Silurian volcanism of the Skomer Volcanic Group in the Caledonides of south Wales

Basaltic, andesitic and rhyolitic volcanism was widespread during Ordovician time in the Welsh, Basin. Minor Silurian volcanic rocks occur in the Welsh Borderland and in Pembrokeshire (Dyfed), where they represent the youngest volcanic activity associated with the Caledonian orogeny in Wales. The Skomer Volcanic Group comprises c . 760 m of lavas and pyroclastic rocks with minor sedimentary rocks which are best exposed on Skomer Island but crop out over 43 km from the Smalls and Grassholm (in the Irish Sea) to mainland Pembrokeshire. New chemical analyses have been used to characterize these rocks and to compare them with earlier Ordovician volcanic rocks. The Skomer Volcanic Group comprises hawaiite/mugearite lavas and rhyolitic flows and pyroclastic rocks. The rhyolitic rocks are subdivided into a high-Zr group, (originally of peralkaline composition) and an unrelated low-Zr group. The hawaiite/mugearite lavas and high-Zr rhyolites are considered to form a single group, related by fractional crystallization, analogous to basalt–hawaiite–mugearite–comendite associations erupted in within-plate oceanic and continental settings. However concentrations of high field strength elements (Ti, Zr, Nb, Ta, Hf) suggest that the parent magmas may have been derived from a within-plate (ocean island basalt) source modified by the effects of earlier or contemporaneous Caledonian subduction.

The filoplumes of the Manx ShearwaterPuffinus puffinus

Sexual, geographical and age-related variation of filoplume feathers was investigated in the Manx Shearwater on Skomer Island and Rhum. More breeding males than females had filoplumes and those that had them had more. Skomer birds had significantly more filoplumes than Rhum birds. There was a significant increase in the occurrence and number of filoplumes with age. In contrast to breeders, immature females had a higher occurrence and number of filoplumes than males. Filoplume counts are as useful as morphometrics to sex breeding Manx Shearwaters, but much less useful than cloacal or vocal sexing. The proportions of male and female Bulwer's Petrels with fib plumes were similar to Manx Shearwaters. There was, however, no significant sexual difference in the number counted. The filoplumes of nocturnal petrels are probably of little functional value in sex recognition, particularly when compared with the vocal differences that exist.

Populations of the Bank vole (Clethrionomys glareolus) and Long‐tailed field mouse (Apodemus sylvaticus) on skomer island, Dyfed

The methods used to study the populations of the Bank vole and Long‐tailed field mouse on Skomer Island in 1981 are described. The survey was a repeat of one performed in 1960 and the methods used were almost identical.The distribution of both species of rodent over the island was studied using trap lines and was found to be similar in both surveys.The vegetation of the island was divided into nine categories and the habitat preferences of both rodent species assessed. These have remained distinct and, as in the previous survey, the voles were found to be most strongly associated with areas of deep bracken with little undercover and the mice with open areas such as cliff tops and rocky outcrops.A crude survey of the distribution of the nine vegetation categories was undertaken, a vegetation map was prepared, and the area of each category was estimated. Two trapping grids were established in vegetation categories favoured by the voles. The data from these grids were used in conjunction with the vegetation map to estimate the population of voles over the whole island. Insufficient data were available for such an estimate to be made of the size of the population of mice.

Further studies on puffinosis, a disease of the manx shearwater (Puffinus puffinus)

Epizootics of puffinosis occurred on Skomer Island during the period from late August to mid-September 1978, 1979, and 1980. They affected shearwater fledglings in well-defined areas on the island which were the same for each of the 3 years of study. In contrast to previous reports puffinosis was also recorded in young chicks and full-grown birds.

The contributions of genotype and sex to variation in mating behaviour between geographical subspecies of the bank vole ( Clethrionomys glareolus scheber)

The sexual behaviour of bank voles from the mainland of Great Britain, and from the island of Skomer, differs in a number of respects. Voles from the mainland population show in general greater sexual activity. These variations may be understood as adaptations to ecological differences, particularly in population density. The reciprocal hybrids resemble the mainland population in a number of aspects of their mating behaviour. The possible evolutionary importance of this dominance is discussed. The behaviour of the bank vole is put into the perspective of generalizations made about other mammals. The separate influence of the male and of the female on quantitative variation between the two forms was investigated by studying mating between members of different populations. Some aspects of mating behaviour are shown to be due primarily to the male, others primarily to the female and others to the particular combinations involved. This situation is discussed in relation to the separate action of natural selection on members of each sex.

Timing of Breeding of Common Guillemots Uria aalge at Skomer Island, Wales

Timing of Breeding of Common Guillemots Uria aalge at Skomer Island, Wales

Survival Rates and Breeding Biology of Puffins on Skomer Island, Wales

Puffins Fratercula arctica were studied on Skomer Island, Wales (51?44'N, 5019'W) during 1972-77. Annual survival of breeding adults was 95%. Each year, 20-27% adults were without nesting burrows, and 2% were absent from the colony. 64% of pairs with burrows fledged a chick, with 5-16% not laying, 22-25% eggs not hatching, and 5% chick mortality. Much of the egg loss was caused by disturbance from prospecting Manx Shearwaters Puffinus puffinus which competed with Puffins for burrows. Data on the feeding and growth of chicks is given. Young Puffina first returned to the colony at two, or more usually three, years old. Four years was the earliest age for first breeding. At least 10-16% fledglings survived to four years old; it was not clear whether enough survived to replace adult mortality.

Population Parameters for the Common Guillemot Uria aalge

A number of population parameters for the Common Guillemot are presented, derived from a study of marked birds on Skomer Island, Wales, and from recoveries of ringed birds. Breeding success on Skomer averaged 0.7 chicks/pair, and in two years adult survival averaged 91.5%. Guillemots returned to Skomer in their second year, and prior to breeding birds congregated in clubs. Guillemots first bred at four years old, but most of them probably breed for the first time in their fifth year. Two different estimates for the survival rate of birds up to five years old were: 16% and 20%. Juvenile survival calculated from ringing recoveries varied from 27% for southern England, where numbers are stable or decreasing, to 41% in north-east Canada, where numbers have increased. Between 1972 and 1977 the Skomer Guillemot population remained at a similar level. If adult survival is 91.5% and 100 pairs of Guillemots produce 70 chicks, 17 (24%) of these must survive to breeding age to maintain a stable population. Factors influencing population size are discussed.

Mammalian prey of the Barn owl (Tyto alba) on Skomer Island, Pembrokeshire

Mammalian prey of the Barn owl (<i>Tyto alba</i>) on Skomer Island, Pembrokeshire