At nearly a metre long, it was the Australian magpie nest that stunned researchers.
"The nest was basically made up of coat hangers, electrical wire, saw blades, cable ties and, I think, the plastic 3D glasses were right up there with one of the most surprising things you find," said ecologist Kathy Townsend.
"We envisioned that it had a safety pin through its beak because it was very hardcore."
Marine scientist Dr Townsend and ecologist Dominique Potvin from the University of the Sunshine Coast studied nearly 900 preserved bird nest specimens collected between the years 1832 and 2018.
Their world-first research on bird nests at Museums Victoria and the CSIRO in Canberra was published this month in the scientific journal Oecologia.
It was the first study of its kind to use museum specimens to determine the effects on wildlife in rural and urban backyards.
Post-war pollution
The researchers found that more than 30 per cent of modern-day nests had manmade debris in them, but that was not always the case.
"And the first thing we see are bits of [things] like newspaper and cotton thread and then material, so of course that's still biodegradable."
But things changed in the 1950s post-war era when the first piece of plastic appeared in a nest.
"It was a piece of plastic string found in a nest that was from Melbourne and that 1950s time period related to the time when plastic polymers were starting to become more available across Australian society," Dr Townsend said.
She said the number of manmade materials — mostly plastics — in nests coincided with the urbanisation in Australia and increased from about 4 per cent in 1832 to almost 30 per cent in 2018.
Co-author Dr Potvin said while the presence of plastic in nests may have made nests stronger, it was detrimental to birds' health.
"If you have material that can't break down in your nest, you're far more likely to become entangled and possibly injured [or] have an accidental amputation," she said.
'They're smart'
Dr Townsend said as well as pollution, the number of nest parasites increased over time which they believed was linked to the amount of eucalyptus leaf in the nest.
"So we think that there might be some connection between using some of those natural eucalypt-type materials in the nest, which help reduce the number of parasites that are in there as well.
"They're smart these birds."
During the research, the ecologists looked at the nests of more than 60 different Australian bird families.
Dr Townsend said in contrast to the "not very complex" seabird nests, the complexity of terrestrial bird nests was astounding.
"As a marine scientist coming in to look at this amazing array of terrestrial nests, it gave me a real appreciation for just the intricate structures and how complex and diverse Australia's bird community is in generating these nests," she said.
"Some of them are just beautiful little woven structures; like the rufous fantail, for example, uses only just fine grass and spiders' webs to create their nest and they're beautiful little delicate structures.
