THE EFFICIENCY OF DETECTING COLOR-BANDED HERRING-GULLS (LARUS-ARGENTATUS) AND LESSER BLACK-BACKED GULLS (LARUS-FUSCUS) AT THE BREEDING COLONY - PRACTICAL IMPLICATIONS FOR THE DETERMINATION OF ADULT SURVIVAL RATES

The efficiency of finding color-banded Herring Gulls (Larus argentatus ) and Lesser Black-backed Gulls (L. fuscus) during repeated visits to a mixed species breeding colony on the Isle of May was investigated. T he most efficient period for finding Herring and Lesser Black-backed G ulls was May and June, coincident with the main incubation and early c hick-rearing periods. Ten ''searches'' during that period found 85%-90 % of surviving individuals, while 4 searches found >70%. Additional se arches produced very few extra birds. When assessing annual survival r ates from resightings of color-banded individuals, marking a relativel y large study population is a more efficient method of increasing the precision of survival estimates than additional effort searching for r emaining, unseen birds.