The spacing behaviour and breeding of shelduck on the River Ythan Estuary, Scotland, was studied during 1970 -1972. Sixty percent of the study population were individually colour-ringed; the marked sample did not introduce bias. Birds returning to the study area during December - March associated in flocks, individuals joining that flock nearest their previous year's territory. During the breeding season, the population comprised territorial pairs and a non-breeding flock (one and two-year olds and unmated adult males). Pairs returned to the same territory each year. Territorial behaviour was studied in detail and showed that the precise location of the territory shifted constantly throughout the breeding season. Average territory size was 4.0 ha. A single statistic was devised in describe both the size and the pattern of utilization of parts of the territory. All territorial pairs attempted breeding but only 37.5% appeared with ducklings. The main cause of nesting failure was thought to be disturbance at the nest burrows by other, mainly non-breeding shelduck. Ducklings were reared in confined nursery areas, fledging in approximately eight weeks. Within each nursery area, ducklings frequently transferred from one brood to another; this creching was the result of a high density of broods. Creched ducklings suffered a higher mortality rate than those reared in family units. Most ducklings died during their first week of life (causes mainly unknown) and 9 - 37% ultimately fledged. This production was insufficient to replace adult losses0 There was no evidence that the size of the Ythan population was internally regulated and immigration was considered the major factor maintaining the population at its present size (153 - 179). Factors controlling the extent of this immigration remain unknown.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:593823 |
| Date | January 1973 |
| Creators | Williams, Murray |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU394633 |
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