Pāteke update on Aotea | Great Barrier Island 

TESS van der WELL (Biodiversity Ranger), Dr. LEIGH JOYCE (Acting Senior Ranger Biodiversity), Dr. SARAH DWYER (Supervisor) (Department of Conservation, Aotea | Great Barrier Island)

Pāteke/brown teal (Anas Chlorotis) are an endemic dabbling duck that were once abundant and widely distributed throughout New Zealand(1) but are now classified as ‘Threatened – nationally increasing’ according to the New Zealand Threat Classification System(2). Pāteke are most abundant on Aotea/Great Barrier Island, Northland, and Coromandel, with an estimated total population of 1000-5000(2)(3). The threat classification has a qualifier of ‘Conservation Dependent’ meaning that pāteke need help for their population to recover(2).   

As omnivores, pāteke are known to feed on at least 78 taxa including vegetation, fungi, and various terrestrial and aquatic invertebrates(4). Their varied diet means they can live in a range of habitats such as wetlands, ponds, lakes, estuaries, swamp forest, streams, and rivers. Adults are mainly nocturnal, usually staying hidden in the grass or overhanging vegetation during the day and coming out at night to forage. Young ducklings also feed during the daytime accompanied by the female parent, which makes them more vulnerable to predation. Given their varied habitat use and nocturnal behaviours, the summer months provide a good opportunity for population monitoring when the birds flock to find a mate and strengthen mating bonds(5). The Department of Conservation (DOC) and local community have undertaken annual flock counts to monitor pāteke population trends on Aotea since 1994 (Flock count results are outlined in Annual Pāteke Reports(6)). The methodology follows the National Guidelines for Monitoring Pāteke(7) with all flock sites counted on a single day during February/March and repeated a further two times to obtain the best overall count. While the methodology is known to have limitations, it provides a long-term data set to track general population trends. It should also be noted that a flock count is not a population estimate nor is it a count of the number of individual birds on the island. 

During the 2022 annual flock count, pāteke were counted at 41 sites across Aotea(6). The 2022 total flock count of 465 pāteke showed a slight increase, compared to 447 birds recorded in 2021 and 429 birds in 2020(6). The overall trend since the 1990s indicates that the Aotea pāteke population has been declining, with a significant rate of decline between 1994 and 2000, fluctuating counts of between 530 and 927 from 2002 to 2010, and relatively low counts from 2016 onwards. The lowest count of 429 pāteke was recorded in 2020. Although the flock counts indicate an overall decline in pāteke numbers some of the variation may be due to pāteke moving to new sites, which could result in a full count not being recorded. For example, the Burrill’s drain flock count declined from a maximum of 146 pāteke in 2019 to 8 birds in 2020, and although there is no clear explanation for this decrease, it may be partly due to birds flocking at new locations. Seasonal variation and environmental factors may also affect flock count numbers, and it is interesting to note that the Burrill’s drain flock count increased in 2022, with a maximum of 129 birds recorded(8). Pāteke are known to move sites, especially if old flock sites have less stable pond habitats prone to drying out during drought conditions. Northland flock sites had an “expansion” of range leading to pāteke population count increases (rather than increases at old established flock sites) so it is important to regularly search for new likely flock locations (Nigel Miller pers. comm). It will be interesting to see if the last 12 months of “damp” conditions is reflected in the 2023 annual flock counts (hopefully as a result of improved breeding success). 

As for many native bird species that have experienced significant declines since the 1800s(9), there are numerous contributing factors to consider when trying to understand the reasons for the decline in pāteke numbers on Aotea. To help pāteke recovery on Aotea, DOC has primarily focused on feral cat trapping, pūkeko control, and pond and waterways restoration. However, as John Ogden notes in Issue 36 of Environmental News, the pāteke population has not recovered as would be expected with ongoing predator control at Whangapoua(10). Predation by feral cats is probably a significant contributor to pāteke mortality, however the causes of decline are complex and most likely due to a combination of factors, including predation, habitat destruction, drought conditions, food availability and starvation. More research and monitoring is needed to determine what factors are having the greatest impact on pāteke survival and recruitment. Evidence and anecdotal observations identify predation by feral cats, pūkeko and harriers; and rats are known to prey upon eggs and compete for food. Other threats include habitat degradation, competition for resources by paradise ducks and mallards; and predation by eels and ruru/morepork, however the most significant threat of predation is from introduced carnivorous mammals(7). Climate change may have long-term implications for survival rates and changes in behaviour, with increasingly dry seasons and drought on Aotea affecting water quality, pond levels, wetland habitat and food availability, with juvenile pāteke dying of starvation. In 2021, the Department of Conservation established a dedicated pāteke Biodiversity Ranger role to try and gain a better understanding of the complex pressures affecting the pāteke population on Aotea, with a view to managing the most significant pressures.  

Additional Flock Counts

In 2021, additional monthly flock counts were conducted throughout the flocking season (November to January) at the main flocking sites around Whangapoua and Harataonga to observe dispersal trends. Large variations were seen among counts across the different sites during the 2021-22 flocking season, warranting further consideration of pāteke movements around Aotea, the timing of annual flock counts, and potentially whether birds are moving off island. 

Camera Monitoring

Pāteke nest in shrubby undergrowth near waterways as it keeps them hidden from predators and close to their foraging site(11). Finding nests can be challenging, so a pāteke detection dog was used in July 2021 to locate nests and pathways found at Harataonga, Whangapoua and Awana, in order to monitor hatching success and duckling survival. 

A total of eight nests were discovered with clutch size ranging from 4-7 eggs. Most nests were located within 20 metres of a water body. Five nests were found under punga skirts, two in kikuyu and one on a pōhutukawa tree hidden amongst epiphytic kiekie. Cameras were set up to monitor parent behaviour and hatching success. Unfortunately, not enough data was collected to conclude hatching success, however, the footage showed the parents leaving the nest and eggs left unattended for 30-50 minutes every night. Rats were captured visiting the nest and playing with eggshells but there was no evidence of them preying on unhatched eggs. 

Cameras were also set up along pāteke pathways which were found along fence lines and adjacent to creeks or roads. Pāteke use these tracks daily to commute between roosts and foraging sites(11). Once eggs had hatched, adult ducks were seen taking their ducklings down these pathways to foraging sites. Soon after pāteke ducklings were observed on the pathways, paradise shelducks were seen using the tracks with clutches of up to 17 ducklings. Data from the 2021-22 monthly flock counts also showed high numbers of paradise shelducks (maximum of 163 at Burill’s drain) using the same habitat as pāteke, with the highest numbers towards the end of the flocking season. High numbers of paradise ducks were also seen flocking on Awana Stream in January 2021 (approximately 70) and February 2022 (approximately 60) (Barry Scott pers. comm). The trail camera footage also showed that the pathways were shared with feral cats, rats, pūkeko and feral pigs. 

Monitoring of Feral Cats and Rats

Trap data records identify the number of feral cats captured in recent years, however there is no historical baseline data to estimate long-term feral cat population trends on Aotea. In 2021, DOC established a network of 32 baited trail cameras at set point locations along 8 transects around Whangapoua to monitor feral cats, following the same methodology used by Auckland Council across central regions of the island. Monitoring was undertaken for 21 nights in both May and October in 2021 and 2022, recording the presence of cats, harriers, rats, pigs, rabbits, pāteke, pūkeko, banded rail, paradise ducks, magpies, and shore-wing plovers (however some records may be recounts rather than discrete individuals). 

An index for each species counted in the camera images was determined by the formula: 

The 2021 results showed an increase in cat detections per 1000 camera hours in May (3.7) compared to October (1.1). Harrier detections were also higher in May (19.4) compared to October (5.7), while rat numbers were higher in October (107.6 compared to 65.4 detections per 1000 camera hours). These initial results indicate when pāteke may be most vulnerable to predation, however ongoing monitoring is required to identify long-term trends in feral cat numbers. This information will assist feral cat control, for the Tū Mai Taonga project, and pāteke management decisions. 

Rodent monitoring was set up at Harataonga (4 lines) and Whangapoua (8 lines) in 2021. Each line consisted of 10 tunnels spaced at 50 metre intervals. Monitoring started in November 2021 and records were taken four times (in February, May, August, and November) to align with the existing island-wide rodent monitoring. Initial rat tracking index (RTI) results for November 2021 were 35% at Whangapoua and 28% at Harataonga. 

Predator Control

Cat trapping efforts varied in terms of the number of months per year control was carried out in the Whangapoua basin. Feral cat control was only undertaken during April-September between 2013-2017. This increased to nine months of the year from 2018 onwards in response to the declining pāteke population, and then to year-round trapping in 2021. Conibear (quick-killing body-gripping traps) and live capture traps were set around Whangapoua basin along roads and near sand dunes. Following a review of the network in 2021, additional traps were added at the edge of the bushline. 

Pūkeko are known to eat both ducklings and eggs and large numbers can have an impact on pāteke breeding success due to habitat competition(12). Pūkeko control by shooting and cage trapping commenced in 2001 and continued until 2015 before it was reintroduced in 2017, with more intensified control during the pre-breeding season in 2021 and 2022. 

Wetland Restoration

To increase pāteke foraging, breeding and roosting sites, DOC has managed ponds and wetlands around Whangapoua, including undertaking weed control and native planting. In 2021, roughly 2600 plants were planted near waterways and ponds around Okiwi to provide suitable habitat for pāteke. Mercer grass, Mexican devil, lotus major and kikuyu are known to grow into dense mats reducing areas of open water, choking waterways, and reducing the ability for pāteke to feed. Last year the Whangapoua wetland management plan was reviewed and updated, and a work plan was created to include both weed control and planting. 

Conclusion

DOC is continuing existing predator control, habitat restoration and monitoring in partnership with the Aotea community and Auckland Council, and new monitoring initiatives will help identify where future efforts and resources should be directed. Pāteke will also benefit from feral cat and rat control undertaken by the DOC Jobs for Nature funded Ngāti Rehua Ngātiwai ki Aotea-led Tū Mai Taonga project. The pāteke programme is the main focus of acting Senior Ranger Biodiversity, Dr Leigh Joyce (who is on a 14-month secondment while Louise Mack is on maternity leave). The plan is to finish the draft Pāteke Literature review and gather information from existing scientific research, publications, reports and monitoring – to collate what we already know about pāteke on Aotea and identify areas where knowledge and data is lacking; to be able to prioritise further research and help determine ongoing management decisions so that we can prevent further decline and protect pāteke. In order to utilise resources effectively, we need to gain a better understanding of the complex factors threatening the pāteke population on Aotea. It is important to identify gaps in our knowledge, including available information on nesting, duckling, juvenile and adult survival rates, recruitment, and causes of mortality, so that we can determine when pāteke are most vulnerable. 

DOC is planning a community hui in September to discuss ideas and the possibility of setting up a community “citizen science” website specifically for pāteke on Aotea. There is a wealth of local knowledge in the Aotea community and observations about pāteke behaviour, threats, flock sites and long-term trends in numbers - and it would be fantastic to capture this knowledge and involve the community and schools in monitoring and recording current and historical information to help manage the pāteke population. 

Acknowledgements

Thank you to all those in the Aotea community who have been trapping in their back yards, restoring wetlands and waterways, and participating in pāteke flock counts. 

References:

1. Worthy, T.H., 2002. Fossil distribution of brown teal (Anas chlorotis) in New Zealand. Wellington, UK: Department of Conservation. 

2. Robertson, H.A., Baird, K.A., Elliott, G.P., Hitchmough, R.A., McArthur, N.J., Makan, T.D., Miskelly, C.M., O’Donnell, C.F., Sagar, P.M., Scofield, R.P., and Taylor, G.A., 2021. Conservation status of birds in Aotearoa New Zealand, 2021. 

3. O'Connor, S.M., Maloney, R. and Pierce, R.J., 2007. Pateke (Anas chlorotis) recovery plan, 2005-10. Science & Technical Pub., Department of Conservation. 

4. Moore, S.J. and Battley, P.F., 2003. Cockle-opening by a dabbling duck, the brown teal. Waterbirds, 26(3), pp.331-334. 

5. Sheridan, K. and Waldman, J., 2020. Evaluating the success of reintroduction of Pāteke (Brown Teal) to lake and forest habitats in a predator‐controlled preserve in New Zealand. Ecological Management & Restoration, 21(3), pp.237-246. 

6. Mack, L. 2022, Department of Conservation: GBI Pāteke Project – Annual Report 2021-22 (Draft).

7. Pierce, R.J.; Maloney, R.F.; Neill, E.; O’Connor, S.M. 2003: National guidelines for monitoring pateke (brown teal)—second edition 2003. Wildland Consultants Ltd Contract Report No. 477. Prepared for Department of Conservation, Wellington (unpublished). 33 p 

8. Giblin, S. 2021. Pāteke Literature Review. Aotea – Great Barrier Island 2021 (draft). Department of Conservation. 

9. Hayes, F.N. and Williams, M., 1982. The status, aviculture, and re-establishment of brown teal in New Zea-land. Wildfowl, 33(33), pp.73-80.

10. Ogden, J., 2016. Pateke population trends and the impact of predator control, Great Barrier Island. Great Barrier Island Environmental News, 36.

11. Lewis, D.M., 2018. Resource selection by New Zealand pāteke/brown teal (Anas chlorotis) at two North Island locations (Doctoral dissertation, University of Otago). 

12. Watts, J., Maloney, R., Keedwell, R., Holzapfel, A., Neill, E., Pierce, R., Sim, J., Browne, T., Miller, N. and Moore, S., 2016. Pāteke (Anas chlorotis) population trends in response to predator control on Great Barrier Island and Northland, New Zealand. New Zealand Journal of Zoology, 43(3), pp.258-274.