The Environment Protection Authority (EPA) is seeking assistance from members of the public after 15 satin bowerbirds died from chemical poisoning in Modanville, near Lismore, in the past few weeks.
Investigations conducted by North Coast Local Land Services have confirmed that the bird deaths were caused by the banned insecticide Fenthion.
As the responsible regulator for pesticide use, the EPA is exploring the possibility that the birds may have been deliberately targeted. No other bird species is known to have been impacted. Satin bowerbirds are a protected native species.
EPA Manager Regional Operations North Coast Benjamin Lewin said the killing of native birds, whether through intentional or reckless pesticide misuse, was a serious offence.
"We are encouraging anyone with information on these deaths, or anyone who may have seen some activity that could be related to this illegal baiting, to contact the EPA as soon as possible," Mr Lewin said.
Fenthion, which was banned from use in 2014 with a phase out period of one year, is a broad-spectrum organophosphorus insecticide. Fenthion is extremely toxic to birds and substantial penalties exist for the possession and use of Fenthion. The chemical was widely used in the past for insect control on a broad range of fruit crops and for external parasite control on livestock.