152 Notornis, 2016, Vol. 63: 152-166 0029-4470 © The Ornithological Society of New Zealand Inc. Changes in the status and distribution of Australasian bittern (Botaurus poiciloptilus) in New Zealand, 1800s−2011 COLIN F. J. O’DONNELL Science & Policy Group, Department of Conservation, PO Box 4715, Christchurch 8140, New Zealand HUGH A. ROBERTSON Science & Policy Group, Department of Conservation, Private Bag 5, Nelson 7042, New Zealand Abstract We collated and reviewed 4179 records of the historic and contemporary distribution of the endangered specialist wetland bird, the Australasian bittern (matuku,Botaurus poiciloptilus), in New Zealand, to assess its current status and trends in its distribution across major habitat types. We mapped distribution in 5 time periods (pre-1900, 1900−1949, 1950−1969, 1970−1989, post-1990). We found that Australasian bittern are currently found throughout New Zealand with strongholds in Waikato, Northland and Auckland regions (46% of records) in the North Island, and Canterbury and West Coast (22%) in the South Island. They occur widely in freshwater and brackish riverine, estuarine, palustrine and lacustrine habitats. Australasian bittern were abundant (records of groups >100 birds) in Māori and early European times, but historical maps indicate their range appears to have been reduced by c. 50% over the last hundred years, with the most dramatic shrinkage in range occurring post-1970. Marked declines in occupancy began in Otago, Canterbury, Waikato, Wellington and Auckland regions between the 1900-1949 and 1950-1969 periods and reductions in range have been steady since. In comparison, declines in Northland, Southland, West Coast and Tasman/Nelson appear to be more recent and greatest between the 1970-1989 and post-1990 periods. The apparent shrinkage in range is supported by numerous observations in the literature. Australasian bittern distribution is now biased towards coastal areas and lowland wetlands of the North Island. Information indicates that range reductions were paralleled by marked declines in numbers: 34% of pre-1900 records were >1 bittern and 7.3% were >10, whereas post-1990, only 19% of records were >1 and 0.7% >10. The clearance and drainage of wetlands (c. 90% loss) and shooting were major causes of declines, but contemporary threats include continued habitat loss and degradation, accidental deaths from a range of causes, and predation by introduced mammals. Current trends in Australasian bittern populations suggest that they should be reclassified as Nationally Critical under the New Zealand threat classification system. Conservation management should focus on restoration of hydrology, water quality and aquatic food supplies, predator control, reedbed management and maintaining regional wetland networks. O'Donnell, C.F.J.; Robertson, H.A. 2016. Changes in the status and distribution of Australasian bittern Botaurus( poiciloptilus) in New Zealand, 1800s-2011. Notornis 63 (3-4): 152-166. Keywords swamp birds; wetlands; habitat use; threatened species; conservation status; distribution; habitat loss; bittern INTRODUCTION International 2015). Bitterns are difficult to study, The Australasian bittern (Botaurus poiciloptilus) is largely because they are rare, highly cryptic and a wetland specialist present only in New Zealand, secretive, and inhabit locations that are difficult to New Caledonia and southern Australia, where survey (Poulin & Lefebvre 2003; Gilbert et al. 2005; it inhabits a variety of fresh and brackish water O’Donnell et al. 2013). As a result, little information habitats (Buchanan 2009; O’Donnell 2011; BirdLife has been published on the status, populations, distribution and habits of Australasian bittern Received 29 June 2016; accepted 19 September 2016 (Marchant & Higgins 1990; Heather & Robertson Correspondence: [email protected] 2000; McKilligan 2005). Status of Australasian bittern 153 The Australasian bittern is classed as globally the 1800s to 2011) and describe landscape-scale Endangered by the IUCN (BirdLife International habitat use patterns derived from these data. 2015) and Nationally Endangered in New Zealand (Robertson et al. 2013), because numbers are thought to have been drastically reduced through loss and METHODS degradation of their wetland habitat. Degradation Collation of records of the remaining wetlands continues, with We collated as many records of Australasian bittern fragmentation, water abstraction, pest invasion and as possible between April 2009 and June 2011. To habitat modification being major threats (O’Donnell do this, we undertook computer-based searches 2000; Ministry for the Environment 2007; Ausseil of science publication databases and we contacted et al. 2008; Ausseil et al. 2011). In Australia, recent people in the Department of Conservation (DOC), regional declines in reporting rates of >90% are Fish & Game, Territorial Local Authorities, Te Papa, thought to represent genuine population declines Auckland, Canterbury and Otago museums, the (Buchanan 2009; Pickering 2010) and in New Ornithological Society of New Zealand (OSNZ) Caledonia there have been just 2 recent records (through its newsletters;e.g., Langlands & O’Donnell of booming males (BirdLife International 2015). 2009) and asked for records. We also searched the on- In 2011, the Australasian bittern was listed as line listservers BirdingNZ (www.birdingnz.net) and Endangered under Australian federal legislation New Zealand eBird (ebird.org). Records included (Department of Environment 2016). those lodged with the OSNZ Recording Scheme There is no information on rates of decline in since 1939 and published as Classified Summarised New Zealand, but we predict that the distribution Notes (e.g., Edgar 1972; O’Donnell & West 1996) and of bittern has shrunk at least since Europeans began the OSNZ Atlas Schemes (1969-1979 and 1999-2004; draining wetlands in the mid-1800s. Approximately Bull et al. 1985; Robertson et al. 2007). 90% of inland palustrine wetlands have been For each record we plotted the locations in drained, representing a massive loss of potential ArcGIS (Version 9). Grid references were recorded habitat (Ausseil et al. 2008; Ausseil et al. 2011). as New Zealand TM Projection (NZTM) using Although the extent of biodiversity loss associated the WGS 84 Map Datum. Many historical records with this clearance has not been measured, it is were in either imperial or New Zealand Map Grid likely that the decline in abundance and range of formats. They were converted to the NZTM using species dependent on wetlands has been severe. the Land Information New Zealand web-based Wetland loss also continues to occur in some regions conversion programme (http://apps.linz.govt.nz/ of New Zealand (e.g., Ledgard 2013), highlighting coordinate-conversion/). that further information is needed to quantify the We scored the accuracy of the location of each impacts of land use change on threatened species. record (sighting or calls) on a 4 point reliability It is important to develop a greater scale: understanding of the distribution and abundance of 1. Accurate record. Exact location point known Australasian bittern in New Zealand. If postulated (i.e., where the bird was sighted). declines are continuing, then it is important that conservation programmes focus on ways to 2. Specific habitat record. The location of the reverse these declines. Accurate information on habitat was known and it was associated distribution and habitat use provides baseline with a small polygon (e.g., somewhere information on potential threats to Australasian within a small wetland). bittern populations. These can be used to determine where and at what rates declines may be occurring 3. General habitat record. The location of the and to identify important sites for protection and habitat was known and it was associated management. Such information is essential for with a large polygon (e.g., somewhere within prioritising the timing and location of conservation a large wetland such as Lake Ellesmere, c. actions for this species. Actual population counts 20,000 ha). of Australasian bittern are unavailable, largely 4. Non-specific record. Only the general region because of difficulties in counting them (O’Donnell of the record was known or it was from an et al. 2013). Thus, in this paper we use distribution unknown location within a 10,000 yard records as a surrogate indicator to infer broad or metre grid square from the successive population trends and to explore possible range atlases of bird distribution (Bull et al. 1985; changes (Noss 1990). The aims of this paper are to Robertson et al. 2007). (1) collate a national database of distribution and habitat records of Australasian bittern, (2) describe Any vague or uncertain records were excluded. regional distribution patterns, (3) report on changes For example, numerous study skins in museums had in distribution and reporting rates over time (from no location data or only identified a large provincial 154 O'Donnell & Robertson Fig. 1. Regional territorial local authority boundaries used in analyses of Australasian bittern distribution in New Zealand. region (e.g., Canterbury region). We had no way of of death (if a specimen) attached to them. Records verifying that bittern were accurately identified were categorised according to broad habitat for every record we entered in the database. We characteristics if the information was known. In this assumed records in the published literature were paper, we describe distribution of records across accurate.