The ecology of seabirds on Ailsa Craig, Firth of Clyde

• Main Author: Zonfrillo, Bernard
• Format: Thesis
• Language: English
• Published: 1997
• Subjects: QH Natural history; QL Zoology; Ailsa; Ailsa Craig; Fulmar; Rocky Island; Razorbill
• Online Access: http://theses.gla.ac.uk/71773/; http://theses.gla.ac.uk/71773/1/10391414.pdf; https://eleanor.lib.gla.ac.uk/record=b1711766

The Focus of this thesis is the ecology of seabirds on Ailsa Craig, a remote, high, rocky island situated in the Firth of Clyde in south-west Scotland. The island is principally an internationally important Gannet colony but has locally significant numbers of other breeding seabirds. The status of seabirds on Ailsa Craig and in the Firth of Clyde in general, was examined. Possible reasons for the observed species fluctuations are examined. Selected aspects of the breeding ecology of seven seabird species on Ailsa Craig were studied. These are Fulmar, Gannet, Great Black-backed Gull, Herring Gull, Kittiwake, Guillemot and Razorbill. Diets of adult and young of most species are analysed and the growth rate of young is also examined in most cases from hatching to fledging. Growth rate is presented, in most instances, as both the absolute growth rate and the instantaneous growth rate, the latter being used for comparative purposes since it accounts for variation such as individual size, which may be a factor of sex or clinal variation. Dietary data and chick growth rates largely reflect food availability in the marine environment, and this is discussed with respect to the diet and foraging behaviour of the species involved. Remote seabird islands are usually free of any naturally occurring mammalian predators but when alien mammals are transported to islands through anthropogenic agents the consequences for breeding seabirds can be disastrous. Burrow nesting species in particular can be seriously affected by fast- reproducing predators such as rats. Ailsa Craig was colonised by brown rats through shipwrecks around 1889. Following that time certain seabird species, all burrow nesters, gradually and completely died out. This was generally attributed to the effects of rat predation. The final section of this thesis describes a method whereby rats were eliminated from Ailsa Craig and details the techniques and monitoring methods involved. Following the commencement of rat eradication in 1991, preliminary results indicated increased biodiversity and increases in productivity of some bird species. Other important fauna and flora of the island also increased in the absence of rats. After monitoring for six years, the eradication of rats on Ailsa Craig appears to have been completely successful.