The herring gull is the gull most commonly encountered in Cornwall, with a grey back and red spot on their yellow beak. They live for around 12 years and are highly intelligent birds with strong communication and social learning skills. This has allowed them to evolve strategies to obtain food more easily by stealing it from humans, either when briefly left unattended or by swooping and grabbing from unsuspecting hands.
Whilst their pasty and ice cream stealing antics in coastal resorts might give the impression there are lots around, the coastal herring gull population dropped by about 50% from 1970 to the mid 1980s and the decline has continued with another drop of around 50% up to 2020.
Part of the decline in coastal herring gull populations can be explained by a migration of birds inland to urban areas. Birds have been driven inland in search of food and roosting sites due to declining fish populations and lack of undisturbed coastal nesting sites. In urban areas, streetlights allow gulls to forage by night and there is no longer much competition from red kites, which scavenged the rubbish tips in the Middle Ages.
At the time of writing, a survey of the inland populations is being carried out to determine the relative size of these vs the coastal population and if these are stable. The first datasets from some of the devolved UK Nations suggest that is unlikely to explain the majority of the decline. Since the 1990s, 96% of the population in Northern Ireland died out predominantly from botulism. It's thought that birds seeking food on rubbish tips might be bringing this back to colonies.
The herring gull is an example of a "ring species". In Europe, the lesser black-backed gull and herring gull are distinct species, yet as you circumnavigate the globe, the populations become more similar until they merge in the middle as a single species.
Herring gulls are able to communicate nuances both by altering the frequency and timbre of their calls - conveying, for example, the relative severity of a threat in an alarm call. They also analyse and remember the personality of their neighbours, ignoring more skittish birds but taking action when a more trusted bird raises an alarm.