VARIATION IN LAYING SYNCHRONY IN A SMALL HERRING GULL COLONY

I measured the laying span and laying synchrony in a small Herring Gul l (Larus argentatus) colony over a 12-year period. Herring Gulls in th e study colony adjust their onset of breeding in relation to prevailin g ice-conditions, likely to escape predation, so that late springs lea d to late breeding. Measured with the standard deviation of laying (Go chfeld 1980) synchrony varied in accordance with timing of laying, so that late initiation of nesting produced a higher degree of synchrony. Synchrony did not correlate with the number of pairs in the colony, a nd variation in synchrony is thus mostly a product of variation in env ironmental conditions. The level of synchrony did not affect productio n of young in the colony. The studied group of pairs was very synchron ous compared with other studied Herring Gull groups, possibly because of the pronounced seasonality of the breeding environment they experie nce.