We are delighted to report that native birds have begun to recover in the Perth River valley, just 18 months after our winter 2019 predator removal operation successfully eliminated stoats. In July, follow up actions removed the last resident possum, and we have now almost finished off the last few rats.

We recently analysed almost two years’ worth of native bird detections from our network of 142 lured trail cameras. In the graphs below, these detections are broken down by the percentage of the camera network that detected each species every seven days.

Note:

There are currently two gaps in the data, on November 1-21 and April 14-28, in which footage has not yet been processed. We will update the graphs as soon as this footage review is complete.
The camera network has also infrequently detected ruru (morepork) throughout the survey period.

The lured camera network is low to the ground, and is designed to detect possums, rats and stoats, not native birds. Therefore, these incidental records are unlikely to show the full extent of recovery as a result of the predator elimination. Nevertheless, this network has provided us with rich data about the activity and relative abundance of a wide range of species within the Perth River valley—demonstrating once again the versatility and value of this camera tool.

Highlights

Kea

*Juvenile kea in the Perth River valley, March 2020 (Chad Cottle)*

The Kea Conservation Trust (KCT) and DOC have reported that kea up and down the West Coast double-clutched (mated and raised fledglings twice) during the 2019-20 breeding season.

Our observations in the Perth River valley support this conclusion. Fledgling kea were spotted in the site as early as October 2019, and as late as March 2020, and young kea in different age classes have been seen within the same period. This indicates that kea have had a very successful breeding season, which is likely to be significantly enhanced by the absence of stoats in the valley.

Both ZIP team members and experienced helicopter pilots continue to report frequent kea sightings during their work in the field site, including a memorable encounter with 13 juvenile kea in February 2020, and another with 27 juvenile kea in April 2020.

Kākā

Before the predator removal operation, no kākā were detected on camera in the Perth River valley. Kākā were first encountered by our field rangers in the field site in August 2019, after the completion of the operation. Adults and juveniles have since been detected in the camera network on several occasions, by 12 different cameras throughout the site.

In June 2020, two of our field rangers captured the footage below of a kākā feeding on a rotten standing tree trunk near the confluence of the Perth and Barlow Rivers. Since September of this year, our team has reported increasing sightings of kākā within the same area. In November 2020, kākā were seen for the first time in both the Teichelmann Creek and Lower Barlow areas.

Kākā nest in holes in tree trunks. This makes them extremely vulnerable to predation by stoats, which can kill eggs, chicks and incubating adults in a single attack. A five-year study at Lake Paringa, South Westland, between 2010 and 2015, found that thirty times more kākā chicks were produced in an area after 1080 treatment than in an area where no 1080 was used.

We are therefore pleased, but not hugely surprised, that the successful elimination of stoats from the Perth River valley has led to an increase in kākā sightings. We look forward to seeing this population thrive!

Yellow-Crowned Kākāriki

Before the predator removal operation, yellow-crowned kākāriki were very infrequently heard by our field rangers during the course of their work. They are now regularly heard by field rangers up and down the Barlow Valley, and have been seen beneath the forest canopy on several occasions, including the sighting below in October this year.

Kererū

*A kereru caught on camera in the Perth River valley, June 2020*

Before the predator removal operation, kererū were frequently sighted by our field team. However, no kererū were detected in our camera network until after the first phase of the operation. Over the last year, our team members have regularly seen kererū throughout the field site, and have even occasionally encountered large flocks of 30 or more birds!

Whio

Whio (blue ducks) were detected on just two cameras in the field site during 2019, before the predator removal operation, and on four cameras in 2020. The relatively low number of detections is not surprising, given that whio live on the river, and the camera network is primarily located in the bush! During the 2019-20 breeding season, whio ducklings were spotted on several occasions by members of the ZIP field team in the upper Barlow River area—the first time since we began work in the site in early 2018. In November 2020, rangers reported seeing whio ducklings in two tributaries of the Perth River.

Female whio are especially vulnerable to stoats during the nesting season, and rats and possums have been known to destroy whio nests and eggs, so the elimination of these species is expected to have a positive impact on the Perth River valley whio population.

Whio naturally live at low densities on the large, flood-prone rivers of South Westland, with an average of 1 pair per km of river. The modest increase in whio sightings and detections we have observed since the predator elimination is a very positive indication that the population is beginning to recover in the absence of predators.

Tauhou (silvereye)

Interestingly, silvereye activity appears to be highly seasonal, with dramatic increases in detections during the winter months, and reduced activity during the warmer months. So far, there has been no observable impact either way on the population as a result of the predator elimination.

Ngirungiru (tomtit)

Ngirungiru activity also appears to be highly seasonal; however a general increase in detections can be observed following the predator removal operation. In February 2020, seven months after the operation, ngirungiru detections peaked at 22%, compared with 15% in February 2019.

Ngirungiru are frequently seen by our field team in all areas of the field site.

Kakaruai (South Island robin)

Our team regularly see kakaruai around the Perth River valley. The bird pictured above is a regular visitor to ZIP’s bivvy in the Upper Barlow area.

The footage below was recently captured by one of our field rangers near a tributary of the Barlow River, where a friendly kakaruai cleaned her boot and gaiter.

Kārearea (falcon)

Kārearea are frequently seen and heard around the Perth River field site, including one that is regularly sighted near the Upper Barlow bivvy.

Ruru (morepork)

Ruru photographed in the Perth River field site, July 2020 (Chad Cottle)

Ruru are occasionally seen and heard by our field rangers, and detected by our camera network.

The ruru above was photographed by one of our rangers in July 2020 near a tributary of Scone Creek, after it landed nearby looking rather unhappy to have been woken up!

Koekoeā (long-tailed cuckoo)

Koekoeā have been regularly heard throughout the Perth River valley during spring and summer 2020, particularly around the Upper Barlow River area.

Tūī and korimako (bellbird)

Camera detections of both tūī and korimako have increased during the last year, and both species are regularly seen and heard throughout the field site.

Great news: Native birds are beginning to recover in the Perth River valley!