Researchers have pointed to a potential risk to kākā making a comeback in urban Wellington.

And this time it isn't predators threatening our native parrot species, but lead exposure likely stemming from the city's roofs.

And findings from a just-published study suggests the problem might not just be one for the endangered kākā, but other city bird species as well.

Researchers began investigating after Wellington Zoo's The Nest Te Kōhanga and Massey's Wildbase Hospital saw more kākā being admitted for lead-poisoning treatment.

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To assess levels in the wider urban population, researchers captured and collected blood from 37 free-ranging adult kākā from Zealandia Ecosanctuary, a 225-hectare predator-proof reserve on the doorstep of urban Wellington, where kākā were reintroduced in 2002 as part of a restoration initiative.

They aimed to identify the physiological effects of those exposed to lead, and where the birds were potentially being exposed.

The adult kākā were captured and blood was collected at two locations in suburban Wellington over a nine-month period.

Results from the recently published study showed lead exposure in 43.2 per cent of the birds studied, although no mortality was observed during this study, lead exposure was associated with reduced body condition in kākā.

But the study's lead author, Massey University wildlife veterinarian Dr Aditi Sriram, said that mortality was just part of the picture.

"We know exposure to large concentrations of lead will kill them, but we wanted to see the physiological effects of small amounts of lead over a long-time," Sriram said.

"Zealandia have been monitoring these birds for years, so we were able to join forces with them and their data to see the levels of exposure in kākā and its effect on these birds."

When a bird was acutely exposed to lead and had high-levels of lead in its blood, it could affect their ability to forage - and even effect the reproductive success and make them more susceptible to illness.

Once it left the blood, lead was redistributed to and could accumulate in other places in the body like the liver, kidney, and could even be incorporated into bone.

"This ultimately means that lead can influence population survival long-term."

The kākā with the highest recorded blood lead concentration showed clinical signs of lead toxicity and displayed unusual behaviour, such as approaching people without apprehension, and returning to readily hand-feed from captors upon release.

"We know exposure to large concentrations of lead will kill them, but we wanted to see the physiological effects of small amounts of lead over a long-time," says Massey University wildlife veterinarian Dr Aditi Sriram. Photo / Supplied

Confirming roofing as an urban source of lead exposure would require further investigation, but the researchers found strong evidence that lead contamination from roofs may be an important source.

Lead isotope values of roof-collected rainwater overlapped with kākā blood lead isotope values, suggesting this to be an important source of exposure in this population.

"Since they are regularly sighted on roofs, we thought perhaps they were being exposed to lead-based products such as roofing materials and paint," Sriram said.

"Because of the inquisitive nature of these birds, an expanding urban population, they venture to backyard and roofs attracted by supplementary food from residents."

"Traditionally a lot of research has been done on lead exposure for waterfowl and raptor species through things like lead buck-shot, but not parrot species in the urban environment or through roofing."

Kākā were reintroduced to Wellington in 2002, as part of a restoration initiative. Photo / Supplied
Kākā were reintroduced to Wellington in 2002, as part of a restoration initiative. Photo / Supplied

Following on from this work, a study investigating long-term survival and trends in lead exposure to gain a comprehensive understanding of lead exposure in this population was warranted.

Wildbase Director and study co-author Professor Brett Gartrell said this work highlights a growing problem that wildlife face as they move into our expanding cities.

"Some species of wildlife are adapting to urban sprawl and finding niches in urban environments but this also exposes them to new threats," Gartrell said.

Historically, ammunition had been the most common source of lead poisoning in wildlife, but this study has determined a new threat, he said.

"This study identifies a previously undescribed urban source of lead for wildlife.

"It is likely that other animals drinking from rainwater collecting on urban rooftops are similarly being poisoned.

"It also suggests work is needed to determine the risks to human health."

Gartrell said the observed link between lead exposure and body condition highlighted the potential for lead exposure to affect physiological function and ultimately influence population survival long-term.

"Managing wildlife in urban areas requires a considered and species-specific approach, which includes a thorough understanding of the risks and threats of urban exposure in wildlife," he said.

Massey University wildlife veterinarian Dr Aditi Sriram examines a kaka. Photo / Supplied
Massey University wildlife veterinarian Dr Aditi Sriram examines a kaka. Photo / Supplied

"Exposure to lead is one of many threats confronting kākā inhabiting urban areas, and the long-term success of this population is dependent on appropriately evaluating and mitigating these risks."

Further work was now being done to look at the effects of lead on kākā chicks and tui, with early findings from this research suggesting they are also affected.

The study, published in the journal Science of the Total Environment, was also co-authored by School of Veterinary Science's Associate Professor Wendi Roe and Zealandia Ecosanctuary's Mr Matu Booth.