S. Wanless et al., MODELING RESPONSES OF HERRING GULL AND LESSER BLACK-BACKED GULL POPULATIONS TO REDUCTION OF REPRODUCTIVE OUTPUT - IMPLICATIONS FOR CONTROL MEASURES, Journal of Applied Ecology, 33(6), 1996, pp. 1420-1432
1. Between 1984 and 1988 breeding output of herring gulls Larus argent
atus and lesser black-backed gulls L. fuscus on the Isle of May, Scotl
and was severely restricted by the repeated destruction of clutches of
eggs. 2. Annual censuses showed that the breeding population of herri
ng gulls declined at a rate of 6% per year 1983-92, and then increased
dramatically by 41% in 1993, The number of lesser black-backed gulls
decreased rapidly 1984-87, but then increased gradually before also ri
sing sharply by 68% in 1993. 3. During the period of control, breeding
output was limited to 150-390 herring gull chicks per year and 15-20
lesser black-backed gull chicks. After control measures were relaxed,
output increased to 1917-2709 herring gulls and 331-1018 lesser black
backed gulls. 4. Estimated mean adult annual survival was 88% for herr
ing gulls and 91% for lesser black-backed gulls. There were no signifi
cant sex or year effects, the 3 . 1% difference between the species wa
s significant at the 10% level. 5. A simple demographic model is devel
oped which closely matches the observed changes in numbers of herring
gulls (range of mean absolute percentage error of stepwise predictions
5 . 4-6 . 1%), but which does not provide a good fit to the counts of
lesser black-backed gulls (19 . 7-20 . 9%). 6. This difference appear
s to be due to interspecific differences in recruitment patterns. In m
anagement terms it indicates that: (i) limiting reproductive output ca
n be an effective method of control for herring gulls, but not for les
ser black-backed gulls; and (ii) on the basis of current information o
n vital rates it is possible to predict future population trends of he
rring gulls, but not lesser black-backed gulls.