Kiwi call monitoring is carried out annually by volunteers and Department of Conservation staff sitting out at established listening points scattered throughout the Trust’s management area in Puketi Forest.
Listening is undertaken during May and June, when kiwi calling is at its peak, on fine calm moonless nights. Calls are recorded during the first two hours of darkness on four nights (a total of eight hours per site). By recording the time, direction, estimated distance and sex of each call, the number of kiwi calling within the area can be measured. Although not all birds call, a useful index of the kiwi population is obtained.
Juvenile kiwi don’t start calling until they are 3 or more years old, so the effects of predator control on breeding success are not immediately obvious.
Monitoring was first carried out in 2000, with further listening in 2004 and annually from 2006. There are 15 listening sites in the forest. Two are remote and are only monitored every few years. Results from the ten most regularly monitored sites are summarised in this graph.
There was a decline in call numbers from 2000 to 2004, which might reflect the effect of predation before the start of pest control. From 2004 to 2011, average call rates and the estimated number of kiwi calling increased by about 2.5 times. Numbers have remained similar since.