Birdwatching is one of the most common and popular ways people experience nature. But it’s not often that even the most enthusiastic birdwatcher returns to the same place more than 800 times to witness the changes over four decades.
In a recent paper , we documented 40 years of change in the bird life of a suburban park in Melbourne. Long-term studies such as this, often by citizen scientists, play a vital role in understanding the extent and nature of transitions in bird populations and their implications.
Australians are all too familiar with the devastating environmental changes caused by extreme events such as floods, bushfires and cyclones. Yet gradual but consequential environmental changes brought about by urban expansion, the spread of invasive weeds and animals, and climate change often pass unnoticed.
We observed many changes over 40 years . Some species declined and disappeared, new species became established, others came and went as conditions changed, and a steady stream of rare birds passed through.
An urban park with a long history
Birrarung Park , 33 hectares in size, lies on the Yarra River floodplain, at the confluence of the Plenty and Yarra Rivers.
This area has always been an important meeting place for the Wurundjeri people, whose name for the Yarra River was Birrarung, meaning “a place of mists and shadows” in the Woi-wurrung language .
The park was established in 1984 on what was largely cleared farmland, bordered by a narrow strip of river red gums along the Yarra River. Since then, it has been transformed by extensive planting of trees and shrubs into a mix of woodland and open grassed areas for recreational use. Two ephemeral wetlands provide habitats for waterbirds.
One of us (Mike Connor) visited the Park more than 800 times between 1985 and 2024, and made notes on the birds seen on each visit.
How many bird species were detected?
Over almost 40 years, 153 species of birds were recorded, including 11 introduced species and 35 species associated with wetlands.
A core group of birds were present throughout the 40 years. This includes widespread species of open country, such as welcome swallows and Australian magpies, woodland species such as red wattlebirds and white-browed scrubwrens, and common waterbirds such as Pacific black ducks and dusky moorhens.
Some species, particularly the waterbirds, occurred irregularly, while others were only noted during part of the study period. Notably, more than a third of species (54 out of 153) were rare visitors, seen on less than 1% of surveys. It’s always exciting to see such rarities and it reminds us how many species may visit an urban parkland over time.
What changed?
We noted five main changes in the bird community.
First, revegetation in the early years provided new habitat for forest species, such as the brown thornbill, grey fantail and grey shrike-thrush. The numbers of forest birds seen on visits increased from 1985 to 2000, as trees and shrubs became established. But these numbers gradually declined thereafter.
Second, new species colonised the park. Dry-country species such as the long-billed corella, crested pigeon and little corella have expanded their range into southern Victoria, including the greater Melbourne area.
Some predominantly mountain forest species became increasingly common; these include the crimson rosella, king parrot and yellow-faced honeyeater. The rainbow lorikeet, rare in suburban Melbourne in the 1970s, is now common and widespread, likely because of widespread plantings of flowering native shrubs and trees.
Third, for reasons that are unclear, a suite of species declined and later disappeared (for example, the crested shrike-tit and white-plumed honeyeater). Others remained, but the declining frequency of sightings in later years suggests they too may disappear in the future, such as the willie wagtail and rufous whistler. Surprisingly, several introduced species thought to be well-adapted to urban environments, including the house sparrow, goldfinch and song thrush, also declined and disappeared.
Fourth, colonisation of the park by the noisy miner, an aggressive native species well known to detrimentally affect bird communities in both regional and urban areas, had a profound impact on small native birds.
First recorded in 1998, noisy miners became established across the park by 2004. This coincided with a marked decline in small birds – such as thornbills, pardalotes and whistlers – whose numbers had been relatively stable from 1985 to 2003.
The numbers of wetland species varied greatly through time, responding to fluctuations in rainfall and incidences of drought and flooding. Peaks in numbers corresponded with times when there was plentiful water in the larger of the park’s two wetlands.
A long-term view
Long-term changes, like those we observed at Birrarung Park, are not an exception; they occur in many locations, both in urban and regional areas. But revealing them requires sustained observation, well suited to citizen science.
The dynamic nature of bird communities reflects the ability of many mobile species to move to where suitable habitat is available. But for communities to persist, the mix of suitable trees, shrubs and other habitat has to be preserved.
Urban environments, green spaces and parks, especially those connected along river systems, play a key role in conservation. They offer a variety of food, they facilitate bird movements through cities and towns, and they allow populations to spread into urban residential areas that otherwise have depleted bird communities.
Birdwatching offers multiple benefits: being out in nature, the excitement of detecting a new species, and the opportunity to contribute to understanding of how birds are responding to a changing world.
