Bringing Back the Grey-Faced Petrel/Ōi to Bream Head

BARRY SCOTT (with Adam Willetts and Cathy Mitchell (Bream Head/Te Whara Conservation Trust))

The flight of nine recently fledged grey faced petrels/ōi from Bream Head/Te Whara Scenic Reserve in January of this year marked the third successful breeding season since re-establishment of a breeding colony on the Heads in 2015. This successful outcome was the result of an intensive predator control programme across the reserve and ongoing monitoring of the birds and their chicks throughout the breeding season. As discussions with project manager Adam Willetts and seabird expert Cathy Mitchell revealed, getting breeding success at Bream Head has been very challenging. Increased rodent control around the colony from 2015 onwards quickly led to success with survival of eggs in the 2016 and 2017 seasons but the hatched chicks did not survive because of stoat predation. Further predator control measures led to two seasons of success in 2018 and 2019 but then the presence of one rogue stoat led to a major setback in 2020 with all 10 chicks that were present in burrows on the eastern head being wiped out(1). Restoring a breeding population at Bream Head, one of only a few known mainland breeding sites for these birds(2), is a high priority for The Trust, which was established in 2002.

In July 2015 Adam discovered eight active burrows on the eastern head (Old Woman peninsula) of the reserve while hanging off a pohutakawa tree to scout a new trap line! This discovery led to more intensive trapping of predators around this site. The sign of old burrows here and at other sites suggested that birds had been visiting the Head for many years but because of predation this mainland colony was on the edge of extinction. To assist successful breeding the Trust decided to designate the eastern head, comprising a network of 20 burrows at three locations in close proximity to one another, as a study site. These sites were used to monitor breeding success of the grey-faced petrels in response to various predator control regimes and to use the results of this research as a guide to improve predator control across the Reserve as a whole.

To protect the grey faced petrels from predation by stoats, feral cats and rats, an intensive predator control programme was established around the study site. To target the stoats, double DOC200 traps, baited with fresh salted rabbit, are placed in close proximity to each of the burrows. These are serviced monthly from February through to May and then with the arrival of the birds, fortnightly from June through to January. Rodents are controlled by a combination of toxin (Pindone) feed stations (Philproof) and traps baited with peanut butter. Adam says “it is crucial the bait feeding stations never run out of bait otherwise the knock down of rats will be less effective”. In addition, a network of Steve Allen SA2 traps baited with fresh rabbit are used to target feral cats and stoats. These are checked weekly and reset with fresh bait.

The Grey-faced petrel is an all-dark oceanic bird with a short-hooked beak, long narrow wings with a wingspan of c. one metre. The body is black-brown but the area around the bill and throat is grey, hence its name. At sea it is fast and graceful and around colonies is usually very active on stormy nights. From studies of colonies on islands in the Hauraki Gulf and the West Coast (Bethell’s Beach), we know that the birds return to their breeding sites around April/May, where they re-establish pair bonds, prepare burrows and mate; the so- called prospecting time. They often engage in spectacular aerial displays before mating. After mating both birds depart the site to feed up at sea before returning to the burrow for egg laying, which occurs around June/July.

The male usually returns first followed later by the female who lays a single large white egg and then departs soon after back out to sea to feed. The pair then take turns to incubate the egg in shifts of 2-3 weeks. After the egg hatches in August the young chick is brooded by an adult for several hours to a few days and is then left alone in the burrow while both parents forage for food at sea. At this time the young chicks are highly vulnerable to predation. The chick is fed on average every 4 days but at times is not fed for up to 14 days, corresponding to the two patterns of feeding by the adults; short trip rotations of 1-3 days and long trip rotations of up to two weeks. When the chick is fed the parent may remain in the burrow for several hours but more commonly departs within 30 minutes, especially later in the season. Chicks fledge after 108-110 days corresponding to late December to mid-January. As the chicks mature they lose their down and start emerging from their burrows where they exercise their wings to build up strength for flying. This is thought to be an important time for them to bond to the site and thus return to breed 5 or more years after they depart. By late January the colonies are deserted.

To record the success of these predator control measures the Trust: (i) monitors the presence of predators at the breeding sites with trail cameras, (ii) measures the breeding success of the grey-faced petrels, and (iii) records the presence and breeding of other seabirds at Bream Head. Monitoring of predators is carried out using a combination of tracking tunnels and trail cameras and the results determine what additional measures need to be taken to protect the birds. The breeding success of the grey-faced petrels is monitored throughout the breeding season and includes determining the number of active burrows, the total number of eggs laid and hatched, and the number of chicks that fledge. Many of the burrows are long, so to access them study lids have been installed on a selection of these to record the status of the burrow. To minimize disturbance of breeding birds, endoscope cameras with a blue tooth connection to a cell phone are used to monitor egg laying and the early stages of development. The only time the birds are handled is when the chicks are banded late November before they fledge; an activity carried out by Cathy who has ‘level three’ bird handler qualifications and a permit from DOC for these activities. To monitor the presence of other seabirds around the reserve acoustic monitors are set up at specific times of the year to determine the presence of Cook’s petrels/titī (Pterodroma cookii; Sept-Nov), common diving petrels/kuaka (Pelecanoides urinatrix; Aug-Oct) and fluttering shearwaters/pakahā (Puffinus gavia; Aug-Oct). The first recordings were completed in 2021 and a report on the results is currently in preparation. 

However, predator control is not limited to the study site. A network of traps that target mustelids, rodents, brush-tailed possums and feral cats has been established across the entire 800 Ha reserve. Trapping lines have been set up 100 m apart and parallel to the sea. Some of these lines are along very steep and rugged terrain, necessitating the need for well trained and experienced staff to service them. Traps for stoats (DOC200) and possums (a mix of Steve Allan SA2 and Sentinel) are set at 200 m intervals. In addition, there are 1300 mini toxin feeding stations (Philproof) at 50 m intervals on the trapping lines, across the reserve. The first generation toxin, Pindone, is generally used as it has a very low risk of secondary toxicity and does not accumulate in the environment. However, this toxin is switched out every two years for either Double Tap or 1080 to target trap shy stoats and rodents. All traps and bait stations are designed to be inaccessible to the resident North Island brown kiwi population of around 150. A team of 3 contract rangers and 60 volunteers operate from the Trust base in Peach Road servicing all these traps as well as collecting the SD cards from the cameras, and chew and tracking cards. Servicing and monitoring such a large trap network by rangers and volunteers is a major logistical exercise that is managed by Adam. It also needs to be flexible as detection of predators such as feral cats or stoats requires an immediate response. Consequently, Adam is frequently out in the field auditing and checking everything is running smoothly. 

The intensity of the trapping has led to a reduction of the rat trapping index from ~65% in 2002 to less than 1% from 2015 onwards, which was sufficiently low to allow the re-introduction of birds previously extinct from the reserve, such as the toutouwai/North Island robin (Petroica longipes) and popokatea/whitehead (Mohoua albicilla), and has facilitated the self-reintroduction of kākā (Nestor meridionalis), korimako/bellbird (Anthornis melanura), occasional kākāriki/red crowned parakeets (Cyanoramphus novaezelandiae), and some seabirds around the coast. Possum numbers have fallen from an initial index of 85% (in 2010) to a current index of 0.6% (one possum caught every two months). Removal of possums has had a huge impact on the regeneration of the forest which prior to 2002 was in places very sparse. Suppression of predators has also greatly assisted the breeding and survival of many invertebrates including the Bream Head Skink (Oligosoma kaerakau)(3) and flax snail/pupurangi (Placostylus spp.). In addition to tracking tunnels and chew cards, a network of 33 infrared trail cameras (Browning Dark Ops and Bushnell DS No Glow) paired with automatic lure dispensers (ZIP motolure – with Best Foods mayonnaise), corresponding to one every 25 Ha, has been set up across the reserve to monitor for the presence of feral cats, stoats and possums as part of the Predator Free Whangārei possum eradication project. The use of the trail cameras is an essential component of the control measures so the team know what predators are present and how to respond. From monitoring in the first quarter of 2022 they know that at least six stoats are currently present in the reserve but have failed to engage with any of the traps. With that knowledge the team can introduce more targeted approaches to remove these remaining predators. To further protect the reserve a buffer zone of trapping that extends back to Paua Bay was established in 2021 by Predator Free Whangārei. Trail cameras have been installed across this area as well. This has enabled a ‘detect and respond’ approach to control predators in this buffer zone. Stoats remain the biggest predator challenge for the reserve as they are very difficult to catch, as highlighted by the recent incursions at Motutapu island and Shakespeare Regional Park(3). More promising methods such as the use of toxin-laced rat carcass(4) or toxin laced mayonnaise are being trialled by Zero Invasive Predator (ZIP) together with AI, and may be used in the near future. 

“Understanding predator behaviour is absolutely key to achieving high levels of pest suppression” says Adam. The dramatic decrease in possum numbers was achieved without using any toxins as possums are attracted to visual cues such as white fabric, which they can detect from 100 m or more. They then switch to olfaction for the final few metres that lead them to the baited trap. Trail cameras showed that Norwegian rats, in contrast to Ship rats, do not climb ropes at heights greater than 100 cm from the ground leading to traps, necessitating a change in catch strategy. Observations of rat feeding showed that Norwegian rats prefer meat to cereal baits. Other observations showed that stoats are very weary of any man-made devices in the environment such as traps, and are highly driven by olfaction and learned habits in targeting their prey. These observations and others inform the trapping strategies employed in the reserve. 

The work being undertaken by the Bream Head/Te Whara Conservation Trust is an excellent model of the benefits of community working with the Department of Conservation to restore and maintain an important ecological reserve. The involvement of the 60 plus volunteers together with the Predator Free Whangārei group has established a core group of conservation advocates within the greater Whangārei region. That strong community advocacy has a spillover benefit for conservation in the wider region. As outlined above the maintenance of a mainland area relatively free of predators is hugely challenging and requires considerable people and equipment resources. A key part of the success of this Trust has been the power of observation and follow up trials to better inform their predator control measures. They are ever watchful of new technologies and the need for testing them at their site. Hopefully, as new technologies evolve that make it easier to control predators like stoats, the task will get easier, but meanwhile The Bream Head Trust is very dependent on ongoing funding and support from their strong network of volunteers and supporters. Please support them. 

References:

1. Bryant J (2022). Whangarei scenic reserve celebrates victory with survival of chicks. Northern Advocate, 12 Feb, 2022.

   https://www.nzherald.co.nz/northern-advocate/news/whangarei-scenic-reserve-celebrates-victory-with-survival-of-chicks/R6CNRMV4RBRMFDUIUIM2WJMJFI/

2. Smallman ER (2022). Oi, grey faced petrel making a Raglan comeback. Stuff, Sept 14, 2016.

   https://www.stuff.co.nz/environment/84121485/oi-grey-faced-petrel-making-a-raglan-comeback

3. https://www.reptiles.org.nz/herpetofauna/native/oligosoma-kakerakau

4. Scott Barry (2020). The Grey Faced Petrel Colony at Awana. Aotea Great Barrier Environmental Trust. Bush Telegraph #31 Spring 2020.

5. Nichols M, Dent J and Edwards A (2022). Toxin-laced rat carcass baits for stoat elimination. New Zealand Journal of Ecology 46(1): 3453.

6. Veale A (2022). Recent stoat incursion in the Hauraki Gulf. Environmental News issue 45: 32-35.