The herring gull is a supreme opportunist and scavenger that feeds on discarded fish offal, refuse, bird chicks, mammals, eggs, worms and other invertebrates (7). It breeds in colonies (7) and the nest is usually an untidy heap of grass, seaweed and other vegetation (8). Two to six eggs, which are variable in colour and patterning, are laid after April. Incubation, which is carried out largely by the female (7), takes between 25 and 27 days (8). Both parents share parental care of the downy chicks, which fledge after around 30 days (7).
This familiar gull can be distinguished from other gulls by its large size and grey upperparts (2), which earn it the alternative names of 'silver back' and 'silvery gull' (6). During summer, adults have white heads, but in autumn they become streaked with brown (2). They have bright yellow bills with a red tip, and pink legs (7). Juveniles are greyish-brown; the grey upperparts do not develop until after the second winter (2). A number of vocalisations are produced, including the well-known raucous 'laughing' call (2).
The herring gull has a complex distribution throughout the northern hemisphere, and consists of a number of subspecies. Main areas of population are north-west Europe, eastern Arctic Russia and North America (3). The population occurring in Britain, Ireland, France and Iceland belong to the subspecies Larus argentatus argenteus
(3). Herring gulls breed around most of Britain's coasts; they are absent from some areas of eastern England (3), but are widespread inland during the winter (4).