Gannets (Sula bassana) on Noss, Shetland, with an Analysis of the Rate of Increase of This Species

1. Gannets (Sula bassana L.) on Noss, Shetland, have increased from 1 pair in 1914 to 1518 breeding pairs in 1938. 2. Relations with other birds are discussed. 3. On 29 August 1937 a group of 68 pairs had 57 chicks. 4. Until 1934 or 1935 colonization took place from outside. 5. There is no evidence...

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Bibliographic Details
Published in:The Journal of animal ecology 1938-11, Vol.7 (2), p.305-313
Main Authors: Fisher, James, Venables, L. S. V.
Format: Article
Language:English
Subjects:
Aerial locomotion
Aviculture
Bird nesting
Birds
Breeding
Cliffs
Eggs
Gannets
Mortality
Salmon
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Summary:1. Gannets (Sula bassana L.) on Noss, Shetland, have increased from 1 pair in 1914 to 1518 breeding pairs in 1938. 2. Relations with other birds are discussed. 3. On 29 August 1937 a group of 68 pairs had 57 chicks. 4. Until 1934 or 1935 colonization took place from outside. 5. There is no evidence for colonization after 1935, though it is probable. 6. If gannets were immortal and perpetually fertile, their increase in a closed community would be approximately 25% per annum. In nature, then, an increase more rapid than this must be partly due to colonization. 7. If only one-third of young gannets reach maturity, and once mature are immortal, their increase in a closed community will be approximately 12% per annum. In nature an increase more rapid than this is probably due to colonization. 8. An increase of under 12% per annum gives no clear evidence for colonization. 9. The effect is discussed of such factors as habitat selection, social breeding stimulus, ``conservatism'', possible rate of increase, mortality, supply of nest sites, earthquakes, collectors and man on the history and numbers of a gannet colony.
ISSN:0021-8790
1365-2656
DOI:10.2307/1165