Seasonal change in Melbourne can be viewed in several different ways. A simplistic view, derived from European settlers, is that there are four seasons of equal length, with summer beginning on the first day of December. Another, based on existing Aboriginal calendars in other parts of Australia, is that within greater Melbourne there are several local calendars. These can be distinguished by examining the natural environment - differences in climate regimes, flora, vegetation cover, altitude, aspect, proximity to water, land-management practices, reflective surfaces, drainage patterns and animal and plant behaviour. Aboriginal peoples also predicted seasonal change by coupling significant repeated natural events with changing night-sky patterns. In 1891 J.E. Prince proposed three seasons in southern Australia based on organic objects: the season of growth, the season of maturation or ripening, and the season of rest or equilibrium.
In 1993 Alan Reid suggested the pooling of natural history observations within a region to look for true seasonal patterns. A naturalists' workshop held in Warrandyte in March 1994 achieved this result, and later that year an interim local calendar of six seasons for the middle Yarra region was launched. More current observations collected by a team of observers headed by Glen Jameson, a ranger at Westerfolds Park, adjusted this calendar to the following form:
1 high summer, from early December to early February, when white-throated needletails are seen ahead of the storm fronts, xenica butterflies and beetles appear and young fish come up from the estuaries
2 late summer, from early February to early April, when young birds disperse as others begin to migrate northwards, the Yarra River becomes muddier, young platypuses emerge and eels move downstream
3 early winter, from early April to early June, when morning mists are in the valleys, migrating birds arrive from Tasmania, casuarinas flower, many moths emerge and mixed flocks of insectivorous birds move along the valleys
4 deep winter, from early June to late July, when the weather becomes colder, heavy rains fall, orchid rosettes appear, silver wattles flower and many waterbirds begin nesting
5 early spring, from late July to late September, when more wattles begin blooming, many species of insectivorous birds begin nesting, pallid cuckoos call, orchids flower, joeys emerge from the pouch, cattle egrets frequent the river flats, new shoots appear on aquatic plants and painted lady butterflies emerge
6 true spring, from late September to early December, when seed-eating birds such as finches and parrots begin nesting, platypuses lay eggs, bush-peas and lilies start flowering, the Yarra rises, tadpoles and aquatic insect larvae abound in ponds and spectacular caper white butterfly migrations occur.
A calendar for the upper Yarra region around Healesville was devised by a team led by Dr David S. Jones in consultation with elders of the Wurundjeri tribe. It has a pattern of seven cyclical seasons and two infrequent but overlapping seasons. The seven seasons take the following form:
1 apple, in December, when the kangaroo apple ripens, the Christmas bush and black wattle flower and Peron's tree frogs lay eggs
2 dry, from early January to late February, when kangaroos start breeding, wombats are seen at night and native cherries ripen
3 eel, in March, when eels migrate downstream, swamp gums flower, tiger snakes lay eggs and brushtail possums breed
4 wombat, from early April to late August, when wombats are most active, lyrebirds display, silver banksias flower and rainfall increases
5 orchid, in September, when orchids and flax-lily flowers are numerous, pied currawongs arrive and goannas excavate nesting hollows
6 tadpole, in October, when tadpoles abound and antechinus (marsupial mice) give birth
7 grass flowering, in November, when kangaroo grass flowers, Orion can be seen and lilies flower.
The two overlapping seasons are fire (approximately every seven years) and flooding (approximately every 28 years).
In 1994 Alan Reid launched the Timelines Australia Project, aiming to develop or recover seasonal calendars in each major bioregion. With assistance from Dr Paul Gullan of Viridans, he devised a standardised framework for recording nature event observations to be stored in national and regional databases. A nature diary, Banksias and bilbies, published in 1995 by the Gould League of Victoria, and a Timelines CD-ROM produced in 1998 assist individuals and community groups with monitoring, recording and analysing seasonal events.