The delineation of seasonal dates has long been a subject of debate, with varying criteria applied by different fields and institutions. While meteorological and astronomical definitions of the seasons are widely used, some experts advocate for a more nature-based approach, such as the one observed by ornithologists in the United Kingdom.

According to ornithological tradition, the progression of the seasons is closely linked to bird migration patterns, which have been monitored for centuries. This method divides the year into four periods that correlate with the arrival and departure of different bird species in the region.

Spring, in this framework, begins on March 1, marked by the arrival of early migrant species such as wheatears and sand martins. It extends until late May, when later migrant birds, including honey buzzards, complete their arrival. Summer is considered to start on June 1 and lasts until mid-July, a point some observers find contentious. This period concludes when migrant waders start their southward migration and juvenile birds disperse from upland breeding areas. This timing reflects ecological shifts rather than fixed calendar dates.

Following summer, autumn begins and spans a prolonged four months, typically ending around mid-November. During this season, the country experiences the gradual southward migration of species like woodpigeons, many of which originate from continental Europe, as well as the influx of winter visitors such as redwings, fieldfares, whooper swans, and pink-footed geese. The autumn migration is notable for its extended duration and diversity of bird movements.

Winter is defined by the three calendar months of December, January, and February, during which bird movement is generally restricted to short-range shifts driven by cold weather conditions. These changes are typically triggered by severe frosts or heavy snowfall rather than scheduled migrations.

This ornithological perspective contrasts with other seasonal definitions, including the meteorological seasons used by agencies such as the UK Met Office, which divides the year into four three-month periods based strictly on calendar months. While the Met Office defines spring as March through May, summer as June through August, autumn as September through November, and winter as December through February, the bird-based system reflects ecological processes observable in nature. The differing approaches underscore the complexity of categorizing seasons in a way that balances human convenience with environmental realities.