There's more to our seasons than meets the eye

HABITAT: Brown thornbills live in evergreen eucalypt forests that have mild winters. Picture: Patrick Kavanagh
HABITAT: Brown thornbills live in evergreen eucalypt forests that have mild winters. Picture: Patrick Kavanagh

In mainstream Australian culture, the seasons are determined by calendar dates. Spring began on September 1, and summer begins on December 1.

We follow the same four seasons as Europe, just flipped around to reflect the fact we are in the southern hemisphere.

Let’s think about the traditional European seasons from the perspective of two woodland birds: a small bird that lives in Europe: the blue tit and a little brown bird of eastern Australia, the brown thornbill.

The blue tit lives in deciduous woodland – forests of oak and ash, and very harsh winters. The blue tit only lives for two or three years, has a large brood of nestlings and a very short breeding season. Hungry caterpillars feeding on fresh oak leaves are the fuel for growing chicks. And grow they must! Before the leaves fall, and the insects disappear. It’s the harshness of the winter and the availability of food that determines survival rates of young blue tits each year.

The thornbill lives in eucalypt forest that is evergreen and has long, relatively mild winters. Even at the coldest time of winter, there are still small insects in the bark and in leaf litter. The brown thornbill typically lives for several years, lays small clutches of just two or three eggs over a long breeding season, and often just the one fledgling to care for out of the nest. It’s not harsh winters that determine the survival of a young thornbill – it is avoiding predation while in the nest.

Thornbill parents must place the nest and behave as to avoid the notice of predators such as copperhead snakes and kookaburras. Older parents are better at this, and breeding success usually improves with age.

The biggest differences are firstly that there is food available all year in Australia, and secondly, the harshest season in Europe is mid-winter. Here, the harshest season is actually bushfire season.

The availability of water determines life here in Australia – not temperature. Without water, eucalypt trees stop growing and shed leaves. Grasses have finished seeding at this point, and the animals have finished breeding. Some animals, such as the common brown butterfly, even have a form of summer hibernation called aestivation. After mating in late summer, the females aestivate until the rains come in May.

Beth Gott from Melbourne University expressed this well: “We still think of winter as an unfavourable season for plants, when northern European trees drop their leaves and become dormant. But for our native plants, especially the small tuberous herbs, winter is a season of growth. At this time the bush is green, and the temperatures are rarely low enough to stop growth. The unfavourable season is high summer, when water is scarce, and much of the ground flora becomes brown and dies off.”

Clearly, the European experience does not translate to our little patch of the world.

At the moment, in my bush garden, the young thornbills have long since fledged – they are now young adults learning to find tiny insects with their pointed bills. The parents may have another nesting attempt, as there are still plenty of insects and plant growth before the late summer “dead” period begins in mid-January.

I became interested in nature calendars in the mid-90s when my friend Sean led nature walks in Melbourne, timed so that we could see nature at its best – fungi season in Warrandyte, orchid season at Darebin Parklands, based upon a nature calendar known as the Yarra Timelines. This calendar was developed by Alan Reid, a naturalist who was the heart and soul of the Gould League for many years. Alan’s calendar for the Middle Yarra region has six seasons: autumn, winter, pre-spring, true spring, early summer and late summer. The method was inspired by traditional weather knowledge and calendars used by indigenous cultures.

In 2013, I published a book that built upon and adapted the Yarra Timelines calendar for our region: Daylesford Nature Diary: six seasons in the foothill forests. The book is still available at the information centre, Paradise Books and Beyond the Gate Gallery.

Tanya Loos