BITTERN again! by John Ogden
Environmental News Issue 30 Winter 2013
Photo of bittern chick taken on the hot-springs track on 16th January 2013. Thanks to Herman and the Allom family.
2012 data: Amelia Geary and Steve Corin have produced a draft report on the bittern monitoring organized by Amelia and carried out by a few Brave Barrier Souls over three mosquito-ridden nights last September (2012), and again for a night in November. The results were initially disappointing as not much was recorded by the 24 participants during the total of 95 hours of listening for bittern “booms”. However, the summarized data suggest that at least six bitterns were recorded, and that there is a small breeding population still present on the Island. Amelia also collated and graphed the bittern sightings made since 2008 on Okiwi Station.
Fig 1. Bittern sightings or booming in the Kaitoke Swamp and environs 2000-2013. Dark bars represent the start of summer periods in which nesting definitely occurred (young seen). Black outlines represent years in which booming was recorded.
2000 – 2012 additional data: In September 2006 the GBICT organised a ‘bittern listening’ (17 participants) at dawn and dusk at four locations around Kaitoke swamp and at two locations in the Okiwi/Whangapoua swamp area (Ogden, 2006). Also, there are casual observations by various people, which I have collated since 2000. Although most of these additional data are from areas around the Kaitoke swamp (Kaitoke Swamp, Kaitoke Bridge area , Oxborough’s property, Golf Club and Claris Club, Police Station Swamp), other areas include swamps at Medlands , Sugarloaf Creek, Kiwiriki Creek, Coffins Creek, and the Kaiarara. At the northern end of the Whangapoua estuary bitterns have been seen on the Waikaro block. Clearly, although sightings are few, bitterns are at least occasionally present on swamps throughout Great Barrier Island.
On average only one or two observations have been recorded each year in the Kaitoke area (Fig.1). However it is noteworthy that two definite observations of fledged chicks have been made (2003, 2012) and two other observations of (probably) two birds close together (2006, 2012). Booming indicates that nesting has probably occurred in at least six years.
Booming and nesting occurs in the Kaitoke area from September to January, while on the Okiwi Station most observations are between March and July (Fig 2). These observations are suggestive of nesting in the Kaitoke area and subsequent dispersal (of juveniles?) to the Okiwi Block. Probable bittern booming has also been heard in the valleys draining into Port Fitzroy Harbour (Kaiaraara, Coffins Creek and Kiwiriki) the September – November period.
Fig 2. Summary of bittern observations on Great Barrier Island. Red bars are DOC data from Okiwi Station May 2008 – April 2013 (n=28). Green bars are from locations on or close to Kaitoke Swamp 2000 – 2013 collated by J. Ogden (n= 16). Running mean is the smoothed total of these two locations plus observations elsewhere on GBI (total n=59). Dark green bar (Jan.) represents fledged young.; green with black outlines, all booming observations.
Comparison with earlier data: Bittern was recorded in the first account of the birds of Great Barrier (Hutton, 1868)The number of bitterns found in subsequent studies is similar to that recorded here; Bell and Braithwaite (1964) indicate at least eight birds in 1960, seen or heard at Whangapoua Swamp, Sugarloaf Creek and Kaitoke, while Ogle (1981) records birds at five locations (Kaitoke Swamp, Whangapoua Estuary margin, near Motairehe, swampy pastures central Oruawharo Bay, and near Okiwi airstrip). Bell and Braithwaite visited Great Barrier in June and December, while Ogle’s observations were made in March and April, so the latter’s observations were made outside the usual booming season. Ogle (1981) thought that it was possible that bittern distribution on Great Barrier was being reduced due to habitat modification. Bitterns were formerly more ‘very numerous’ in the swamp behind Whangapoua Bay according to the Mabeys (quoted by Bell & Braithwaite, 1964) and were also frequently seen at Awana before the swamp was drained (Muriel Curreen; personal communication c. 1998). Overall, these earlier reports suggest that bittern were more widespread and abundant than is the case now.
Acknowledgements: To all those people who gave up their evenings or mornings to sit about listening for bitters – a big thankyou! Too many to name individually but you know who you are. Many thanks also to others who phoned or Emailed their observations. The community has many eyes and ears and if data are recorded and collated it is surprising what can be discovered.
References:
Bell, B. D., & Braithwaite D. H. 1964. The birds of Great Barrier and Arid Islands. Notornis 10: 363-383.
Geary, A. & Corin S. 2013. Monitoring Report. Australasian Bittern. Great Barrier Island. 2012. Dept of Conservation. GRBAO-22380.
Hutton, F. W. 1868. Notes on the birds of Great Barrier Island. Transactions and Proceedings of the New Zealand Institute 1: 104-106.
Ogden, J. 2006. The Second Gt. Barrier Bird Count. Environmental News #8 (Spring 2006), See also: GBICT; Biodiversity Advice Fund Report 2. (Ref No. AV207).
Ogle, C. C. 1981. Great Barrier Island Wildlife Survey. Tane 27: 177-200.