Problem

Tarāpunga / red-billed gulls (Chroicocephalus novaehollandiae scopulinus) and tara / white-fronted tern (Sterna striata) nest on artificial structures in the Tāmaki Estuary, Auckland, New Zealand. The Department of Conservation ranks both species as At Risk / Declining (Robertson et al. 2021). Both species have also nested on moored boats in the estuary which creates human-wildlife conflict.

*Piles under Waipuna Bridge (middle, photo taken from land). Photo by Shaun Lee.*

*Piles under Waipuna Bridge (western end, photo taken at low tide). Photo by Shaun Lee.*

Hypothesis

A nesting platform on the large piles (72cm diameter) that rise c2m above Mean High Water Springs (MHWS) under Waipuna Bridge. The piles are safe form mammalian predators who could not swim then climb to the nests. This area is less impacted by light pollution than Panmure Bridge where there is a tarāpunga colony.

Challenge	Solution
The nests are exposed to avian predators including the adjacent tarāpunga.	Using vertical canes to stop flying attacks on chicks. See Preston Dock Common Terns below.
The nest structures might be used by tarāpunga.	This is not a poor outcome but if the spaces are deep and small they might not be so suitable for tarāpunga. There is a small chance that nearby nesting feral pigeons are also interested in the structure.
Colonies are ephemeral (McLean 2018) with birds moving regularly.	This could be an advantage as species with higher site fidelity would be harder to attract. Suggest the addition of a 3D printed decoy to improve the chances of success I the first season.
The structure will attract human attention.	Clearly label the structure as a ‘trial bird nest for endangered terns’ include a phone number & URL to a blog post about the project. Centre the decoy to keep it less accessible / visible to humans. The height of the piles will help deter vandals. Even at low tide access requires a boat or a swim. Graffiti on the bridge may have been enabled by retired pontoons.
Installation difficulties	The piles are tall and using a ladder on a boat is tricky. A platform that connects the piles is visible 2.5hrs after high tide at the western end. A ladder could be used on the platform but it will be slippery.
Monitoring	There is no pedestrian access to the bridge. A land based site inspection from Finn Place identified the western piles as easy to monitor.

*Preston Dock Common Tern nest boxes made by the Fylde Bird Club in Lancashire.*

Tara do not use nesting material (NZBirdsOnline), a small amount of sand could cover the floor of the nests. The Preston Tern Nest Boxes use gravel. Drainage holes should be added to keep water out.

Proposed design

Based on the Preston Dock Common Tern nest boxes. Tara are not much larger than Common Tern but we have made the nest boxes smaller to dissuade tarāpunga form nesting here. Boxes dimensions made of ‘Radiata Premium Grade Smooth Decking 140 x 32mm’. The extra depth allows for a max of 40mm of gravel.

How the nest boxes might attach to a platform on top of the piles.

Timing

Tara tend to arrive at a prospective nesting location only a few days before laying, and there is a high degree of synchronisation of laying within a colony (NZBirdsOnline 2022). Eggs are laid between October-December (NZBirdsOnline 2022). Prospecting may begin weeks before egg laying. We plan to deploy the structure by mid September.

Deployment

The structure was deployed on the 14th of September 2022 (with a few modifications). I had a huge amount of help from a friend who is much more handy with an impact driver than me. The decoy is a bit odd looking as its just a scaled up tara iti with a different paint job. Five tara flew past while we were working and roosted on the piles in the center of the channel. We decided not to deploy the canes until we had active nests.

Update 15 Sep 2022. 10:00am-10:45am.

Four tara and three tarāpunga were roosting on the piles in the centre of the estuary. Every ten minutes or so they would be quite loud with both species calling and jostling for space but no confrontations observed. There were three close passes of the decoy and on at least two of these occasions it seemed like the terns were calling at it. No terns landed on the boxes but both species visited the piles near me. One tern was foraging from a pole which gave it a good view of any fish swimming above the platform in the shadow of the bridge, but it did not dive. One tern dived on in the centre area.

Update 18 Sep 2022. 5:15pm-6pm

About three gulls regularly on the piles in the centre of the estuary. Lots of gull movement and calls, more gull activity between the bridges than the 15th. No terns seen.

Update 28 Sep 2022. 2:15-2:20pm

Constant red-billed gull activity. Three gulls roosting on centre piles. Two pied shags feeding on the southern side.

Update 10 Oct 2022. 1:00-1:01pm

Low tide, no activity. Just a pied shag foraging under the bridge.

Update 23 Oct 2022. 5:00-5:01pm

High tide, no activity. Just a few gulls roosting on centre piles.

Update 02 Nov 2022. 1pm.

Photo taken from pole mounted GoPro shows gulls are prospecting the nest boxes.

A pair of tara have nested on one of the center piles.

Update 26 Nov 2022. 11am.

Two pairs of tarāpunga have nested in the boxes. One of them has really filled it up with material!

Tara also look to be nesting in an adjacent boat.

Update 23 Dec 2022. 12pm

The first pair of gulls have a chick, the second nesting gulls have not increased their nest height at all. Maybe because the other pair can keep watch.

Update 15 Jan 2023. 5:30pm

I’m hoping the chick is in one of the nest boxes and the second nest is not being sat on because it is hot, and the nest has a chick. Alternatively there is another adult down in the nest box. If the recent storms had destroyed either nest or pushed the chick off the adults would likely have moved on.

Update 18 Feb 2023. 5:00pm

The structure is cyclone proof! Weather stations at St Helier’s and Howick recorded wind speeds of 40 knots (74kph). Despite the roosting gulls in the photo I dont think there were any active nests on the structure today.

Additional visit 22 Feb shows nesting material in five of the six boxes. To my knowledge only the two with the most nesting material were used for nesting.

Update 22 Nov 2023. 11:00am

The gulls nested here earlier this year with a chick ready to fledge already. It also looks like at least three of the nest boxes were utilised. There was also a juvenile on a nearby boat and on a pylon under the bridge where tara nested last year.

Update 28 Jan 2024. 2:00pm

The gulls are still using the platform for nesting even tho there is space at the main colony. I think the design is just too appealing to gulls.

References

NZBirdsOnline 2022. https://nzbirdsonline.org.nz/species/white-fronted-tern Accessed August 2022.

Robertson et al. 2021. Hugh A. Robertson, Karen A. Baird, Graeme P. Elliott, Rodney A. Hitchmough, Nikki J. McArthur, Troy Makan, Colin M. Miskelly, Colin. J. O’Donnell, Paul M. Sagar, R. Paul Scofield, Graeme A. Taylor and Pascale Michel. Conservation status of birds in Aotearoa New Zealand, 2021. New Zealand Threat Classification Series 36. Department of Conservation, Wellington. 43 p.

Mclean 2018. Successful restoration of an unnatural breeding habitat for white-fronted terns (Sterna striata). Notornis, 2018, Vol. 65: 54-58. The Ornithological Society of New Zealand Inc.