An influx of native tūī with lead poisoning in the capital may be down to the water sitting in gutters.
The Zoo's animal hospital - The Nest - is seeing an increase in tūī birds with lead toxicity.
The Nest's senior vet Baukje Lenting said it's quite uncommon in nectar eaters.
"These little guys arrive very weak, often very wobbly on their feet and sometimes they have seizures from the poisoning."
Last year, 138 tūī were taken to The Nest and out of 39 tested for lead toxicity, 23 tested positive - about 16 percent of tūī admitted.
Tūī taken into care with poisoning can be treated, she said, although it requires hospitalisation, supportive care and time.
A Massey University study on kākā found that the lead most likely came from water that's sitting in the gutters which the kākā are drinking.
"The tūī, we haven't been able to do the isotope testing yet but based on the behaviour in cities, it's more likely that they're getting it from that same source rather than the other sources that we see wildlife getting lead toxicity from."