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Title: Growth and mortality factors of eider ducklings, Somateria m. mollissima, in North-East Scotland
Author: Mendenhall, Vivian Margaret
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1975
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The growth, survival, and causes of mortality of Eider (Somateria m. mollissima) ducklings were studied on the Ythan estuary, Aberdeenshire, Scotland from 1972 through 1974. Rates of growth of tagged ducklings in the field were variable, and were slower than in captives. Causes of slow growth may have included parasitic infections and food, but cold alone was ruled out in experiments as a cause of retarded growth. Estimation of age in the field from appearance or size of ducklings was unre-liable, although commonly used in other studies. Fiedging success was less than 10%, with most of the mortality in the first two weeks of life. The principal cause of mortality was predation by large gulls (Larus argentatus and L. marinus), which took 80% of all ducklings. Predation was approximately 4 times higher in bad weather than in good. A secondary cause of mortality was parasitic disease; almost all ducklings examined were infected by renal coccidiosis (Eimeria somateriae), but only 8% were estimated to have suffered potentially lethal damage. Food was not considered to be a factor causing mortality; however, it may interact with other factors in bad weather, when some ducklings may fail to obtain a sufficient quantity, and when increased dis-persion while foraging raises the risk of predation. Bad weather did not kill ducklings directly, but was highly correlated with mortality over most years; it is probably the ultimate factor determining survival in most years, acting through others, chiefly predation. Alternate prey for gulls may be responsible for occasional years of very high survival. Broods commonly formed creches of up to 20, but larger creches were a function of duckling density. Creches up to 20 were advan-tageous in reducing risk of predation, but there was no advantage above this size. It was concluded that formation of small creches has been selected for, but large ones are a secondary trait per-mitted by gregarious tendencies and contingent on density.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available