The proverbial canary in the coalmine sprang to mind when I drove the winding road to New Norfolk recently to help compile the annual census of Tasmania’s three gull species.
The old coalmining concept of caged canaries warning miners of the presence of deadly methane gas had nothing to do with the debate about the Adani mine project in Queensland which has revived the canary metaphor in both cartoon and protest poster.
Although the black-throated finch, whose habitat encompasses the mine, has become a symbol for the anti-mine protesters, my thoughts were more focused on how birds have become a barometer for environmental health in a broader sense.
Rachel Carson alerted us to the threat of a silent spring in her book of the same name in the 1950s but the book was not just about falling numbers of birds in a poisoned environment. She also pointed out that the insecticide DDT also posed a danger to humans, and was being detected in mother’s milk.
Birds living in close proximity to humans are ideal subjects for measuring and monitoring the health of suburban and city environments and this is where the kelp, Pacific and silver gulls come into play.
Each year in mid-winter BirdLife Tasmania volunteers spread out across the state to count gull numbers. The exercise is one of the oldest – spanning 40 years – and most comprehensive bird surveys in the country.
I was assigned an area covering both banks of the Derwent from Bridgewater to New Norfolk, plus the eastern side of the river running to the Tasman Bridge.
The gulls were in short supply until I reached New Norfolk and found a good number of kelp gulls splashing in the clear waters of the Derwent and then drying their feathers on the causeway of the New Norfolk rowing club.
For the record, I counted 33 adult birds in crisp black and white livery and 83 immature birds in “salt and pepper” juvenile plumage.
Such a large number of young birds indicated the population of kelp gulls in New Norfolk was in a healthy state but when the overall data from this year was collected it showed lower numbers for all Tasmanian gull species. Numbers, though, are known fluctuate and are actually higher than when counts first stated in the 1980s.
Although researchers have traditionally looked at what affect coastal habitat loss and chemical poisoning have on gull species, the silver gulls in Tasmania have thrown up some interesting facts of their own.
The study of our smallest gull has alerted scientists to the dangers of the bird’s urban diet, which mirrors that of humans because in cities they tend to feed on fast-food.
Comparisons with silver gulls on Bass Strait islands and those in Hobart have shown the latter have high levels of cholesterol, producing ailments like obesity and diabetes found in humans.
It was a fact not lost on me as I munched a double cheeseburger at McDonald’s in Bridgewater mid-way through the survey – outside I counted 15 overweight silver gulls the restaurant’s car park.