Published online by Cambridge University Press: 05 December 2011
The programme for ornithological monitoring in Shetland has concentrated on selected species of cliffnesting seabirds and inshore waterfowl. Sample study sites throughout Shetland have been selected and standard counting methods derived. These have taken account of factors such as logistics and accessibility, the effects of weather and observer error and of the seasonal and diurnal variations in the numbers of birds.
Changes in seabird and waterfowl numbers between 1975–79 have been observed. These, with the exception of the bird mortality following the Esso Bernicia oil spill, have been attributed to natural variation. From the scale and local differences between these as yet short-term observations, estimates are presented of the minimum percentage change required in either numbers of birds or their nests before such natural variation is exceeded.
The problems of interpreting changes in numbers are discussed.
The number of dead birds picked up in Sullom Voe after the Esso Bernicia spill corresponded closely to that estimated from the monitoring counts before and after the incident.