"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," said DoC spokeswoman Liz Brooks.
"We're asking the public to keep looking for red-vented bulbuls and to call 0800 80 99 66 if they think they see one. To encourage this we've increased the reward to $1000 for a sighting call that leads to the response team capturing a red-vented bulbul."
The money will be offered until the end of February 2014.
It is thought that at least five of the angry birds are living in Auckland, arriving in the city 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," said Ms Brooks.
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 have been confirmed 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.
There have also been unconfirmed sightings in Orakei, in central Auckland, and at Walton, between Morrinsville and Matamata in Waikato.
Ms Brooks said the birds have a "very distinctive call, unlike other birds you normally hear".
Their distinctive call can be heard here.