MONITORING MOHUA (YELLOWHEAD) POPULATIONS IN THE SOUTH ISLAND, NEW-ZEALAND, 1983-93

The mohua (or yellowhead, Mohoua ochrocephala) is an endangered hole-n esting passerine which is now absent from > 75% of its former range. T his paper describes an 11 year monitoring programme, which was set up to survey 14 populations at 12 key sites throughout the range of the m ohua, in order to document the pattern of population change and provid e early warning of likely local extinctions. Between 1983 and 1993, on e mohua population became extinct. Five of the 14 populations declined significantly, and three of these were on the verge of extinction by 1993. One population increased, and seven did-not change significantly , although a declining trend was recorded at five of these. Six popula tion crashes coincided with irruptions of stoats (Mustela erminea) fol lowing heavy beech (Nothofagus) seeding.