ANGRY BIRD: The aggressive red-vented bulbul are "prolific breeders" and one of the world's most invasive species.

The bounty on Auckland's most-wanted bird has been boosted to $1000.

Authorities are worried that red-vented bulbuls are on the loose in the city and that the invasive pest bird could become established.

Last month a reward of $300 was offered to anyone providing information leading to the capture of a red-vented bulbul. The reward has been boosted to $1000.

Red-vented bulbuls, which come from Asia, can cause significant damage to fruit and vegetable crops and are known to chase and attack other birds. The Ministry for Primary Industries, Department of Conservation (DOC) and Auckland Council are working together to track and eradicate red-vented bulbuls in Auckland.

"The reward has raised awareness of the red-vented bulbul that's been sighted throughout Auckland," DOC spokeswoman Liz Brooks said.

"We've had more than 70 calls about possible sightings since we offered the $300 reward, a month ago, but are still working to capture one of these birds."

Brooks said people should call 0800 80 99 66 if they thought they had seen one of the birds.

"We think there are at least five red-vented bulbuls in Auckland, which most likely arrived by ship or yacht. They've arrived in Auckland twice before and were successfully eradicated both times.

"They're here again and we want to eliminate them before they make themselves at home."

The red-vented bulbul is one of the most invasive bird species in the world and in New Zealand is listed as an unwanted organism under the Biosecurity Act 1993. The maximum penalty for importing, trading, releasing, exhibiting or breeding a red-vented bulbul is five years in prison or a fine of $100,000.

Red-vented bulbuls were located in three clusters in Auckland: south Auckland (Mangere /Manurewa/ Alfriston), west Auckland (Henderson/Te Atatu / Massey) and on the North Shore (Devonport / Belmont / Takapuna).

There's also been a confirmed sighting on the Whangaparaoa Peninsula.

Unconfirmed sightings have been made in Orakei, in central Auckland, and at Walton, between Morrinsville and Matamata in Waikato.

The red-vented bulbuls is a medium-sized bird, about 20 centimetres long, which is about the size of a starling. It has a black head, a dark back, grey-white belly, and a distinctive crimson-red patch beneath its tail.