A council and a bird expert are mystified at the discovery of hundreds of sodden and dying sparrows.
The New Plymouth District Council received a number of reports of the birds on the ground in the Devon Street East area on Friday.
Between 50 and 100 birds died and a similar number were revived by the local SPCA.
A Taranaki ornithologist, David Medway, says there many places in central New Plymouth where sparrows and other birds roost in large numbers.
"It appears that this happened in only two or three trees in one particular part of Devon Street and I have no evidence that any other sparrows which roost in other trees in central new Plymouth were affected in the same way," he said.
Some of the dead birds are being tested, with results expected by Tuesday.