In August last year a small green pigeon flew across the Tasman Sea – and into the history books. It became the first vagrant bird species to be intercepted at the New Zealand border and put down as a potential biosecurity risk. Te Papa bird expert Colin Miskelly tells the unfortunate story of New Zealand’s first rose-crowned fruit-dove.

Venturing across the Tasman Sea

Australia is a major source of vagrant bird species in New Zealand. Recent examples of Australian species detected in New Zealand for the first time have included a dusky woodswallow in 2014 and a magpie-lark in 2008. Such vagrancy happens many times each year. Australian-sourced vagrant bird species currently in New Zealand include chestnut-breasted shelducks, gull-billed terns and white-throated needletails, while Australian wood duck, glossy ibis and barn owl have recently established breeding populations here. Looking further back into the mists of time, most New Zealand birds have their nearest relatives in Australia, and would have reached New Zealand by flight.

A few New Zealand bird species routinely migrate across the Tasman Sea in large numbers, including Hutton’s shearwater, Australasian gannet, banded dotterel, and white-fronted tern. Several other species use Australia as a staging post en route to migration destinations in other lands (e.g. lesser knot and shining cuckoo), and so birds of many species cross the Tasman Sea in both directions in their thousands every year.

Supertramps

A few bird groups in the south-west Pacific are well-known for their ability to cross large ocean gaps and colonise new lands. Ecologists refer to these groups as ‘supertramps’ due to their high dispersal ability. One of the supertramp groups are fruit-doves of the genus Ptilinopus, with about 55 species spread from Southeast Asia across Oceania. Three fruit-dove species occur in rainforests of eastern Australia, including the subject of this blog – the rose-crowned fruit-dove.

It was a wild and stormy night

FPSO Raroa is a petroleum processing and storage vessel that remains anchored about 1.5 km from the wellhead platform in the Maari oil field, about halfway between Taranaki and Farewell Spit. During the third week of August 2019, the Raroa crew were hunkered down after a prolonged westerly storm that had prevented other vessels coming alongside for several weeks. About 9 pm on the night of 22 August, a crew member found a strange bird hiding in a corner of the process area. The bird was captured and placed in a box, and the decision was made to fly it to New Plymouth during a scheduled helicopter flight the next morning.

Once ashore, the bird was brought to the attention of Biosecurity New Zealand. Images of the bird in its box were shared with the Department of Conservation, Wellington Zoo, and Te Papa, and the bird was provisionally identified as a juvenile rose-crowned fruit-dove. Biosecurity New Zealand staff were advised of the significance of the find as a new record for New Zealand, that (as a natural vagrant) the bird was automatically protected under the Wildlife Act, and that many birdwatchers would be interested in the fate of the bird, particularly if it was released from care.

A grim outcome

After much consideration, Biosecurity New Zealand decided that the bird posed an unmanageable risk to New Zealand, and it was put down that evening. The following information was provided by Biosecurity New Zealand a few days later:

“Rest assured that this was not a decision we took lightly, a number of staff were involved on Friday to ensure the best result was made for biosecurity to protect New Zealand and also the bird.

 “As the bird was brought to mainland New Zealand by helicopter, our main concern was with the biosecurity risk that it posed. Once we had established it was not an endangered species, the options of returning, treating or destroying the bird were carefully considered.

“There was a risk that the bird was carrying pests and/or diseases that we do not have in New Zealand which could pose a threat to our native wildlife. Biosecurity NZ does not have an Import Health Standard for live birds, which means we do not have a benchmark to undertake the tests required to clear the bird of any biosecurity risks. Designing this from scratch for the testing of one bird was not possible to do within a timeframe that avoided compromising the welfare of the bird, which was already deteriorating.

“For these reasons it was decided that the best option was for the bird to be euthanised.”

What is New Zealand?

From a biosecurity perspective, Biosecurity New Zealand considered that the bird had been imported. The Biosecurity Act 1993 defines New Zealand as referring to the land and the outer limits of the territorial sea (12 nautical miles = 22.2 km from the coast). In contrast, the Wildlife Act defines New Zealand (since 1996) as including the Exclusive Economic Zone (200 nautical miles = 370.4 km from the coast). FPSO Raroa is anchored about 73 km from the coast. While on the vessel, the dove was protected under the Wildlife Act, However, once it was placed on a helicopter and flown to the mainland it was considered as an importation, and so Biosecurity New Zealand had a responsibility to assess the biosecurity risk that it posed.

Confirmation of identity

The specimen was donated to Te Papa, where it was prepared as a study skin. Images of the bird, along with a detailed description, and an analysis of diagnostic features compared to related species, were forwarded to the Birds New Zealand Records Appraisal Committee in late December. The RAC accepted the identification of the bird in March 2020. Birds New Zealand uses the same definition of New Zealand as the Wildlife Act. As the dove is considered to have reached New Zealand naturally, the RAC recommended that rose-crowned fruit-dove be added to the New Zealand list.

Two degrees of separation

One of the ironies in this case is that if the dove had flown two degrees either north or south of its chosen course, it could have flown a similar distance and made landfall in Taranaki or Golden Bay. In all likelihood it would have disappeared into the treetops, but just maybe it would have been noticed by an astonished birdwatcher or cat owner.

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