Fenced sanctuaries protect native birds
You’d think this was settled by now, but studies are only now showing that fenced, predator-free sanctuaries on the main islands of New Zealand actually protect native birds.
‘‘These findings provide compelling evidence that fenced sanctuaries effectively conserve native island bird populations,’’ reported three authors in the journal Ecosphere earlier this month.
They also found that native bird species are ‘‘more likely to benefit from invasive mammal eradications than introduced species’’.
In other words, native birds can probably out-compete introduced bird species once mammal predators are removed, a welcome result, said co-author John Innes, a wildlife ecologist with Landcare Research.
Fenced, predator-free sanctuaries on the North and South Islands are relatively new.
The first, Wellington’s Zealandia, was fenced in 1999.
It is to be expected that 10 or 20 years would pass before good data on their birdlife were available for analysis and publication in peer-reviewed journals, Innes said.
Researchers deeply immersed in bird studies have long known fenced sanctuaries work, but the data have largely not been published, he said.
The most recent paper looked at three fenced sanctuaries on the North Island and paired each with a nearby reference site with similar ecology but minimal mammal control. This design set up conditions to test whether fences work.
Researchers compared bird densities in the fenced reserves – Ta¯ wharanui Regional Park on the Northland Peninsula; Maungatautari Ecological Reserve, south of Cambridge; and Rotokare Scenic Reserve, in South Taranaki – and in the paired reference sites in 2016 and 2017.
‘‘Densities of nine endemic bird species were higher in sanctuaries compared to unprotected sites,’’ wrote lead author Sara Bombaci of Colorado State University.
Densities of kaka, north island saddleback, bellbird, redcrowned parakeet, north island robin, and whitehead all improved significantly. There was ‘‘no significant difference’’ for population densities of European introduced birds or relatively recent arrivals, such as grey warbler, fantail and silvereye.
This aspect of the research was a ‘‘novel but not unexpected result’’, said Dr Paul Scofield, a senior curator in natural history at Canterbury Museum.
‘‘It is great that this paper – and a few others recently – give us some solid data’’ on bird sanctuaries, Scofield wrote. He has previously been critical of the poor data available on fenced sanctuaries.
Predator fences will likely have a mixed role in eradicating rats, possums and stoats. On one hand, ‘‘fenced sanctuaries are the only viable pathway for restoring most critically endangered birds to mainland forests’’, according to the recent Bombaci and Innes paper.
On the other hand, players such as Zero Invasive Predators have long said fences are too expensive and porous to be used at scale across the country.
Nonetheless, ‘‘sanctuaries of many kinds are ... showing everyone what Predator Free NZ could achieve’’, Innes wrote.
But the idea that AotearoaNew Zealand could revert to a pre-human state was only a dream, according to Scofield.
The recent paper largely aligns with data and conclusions that emerged from a study of Zealandia earlier this year.
‘‘New Zealand’s novel approach to recovering rare species holds great promise for conserving biota at risk from invasion in other global hotspots of endemism,’’ Bombaci said.
‘‘Predator fences will likely have a mixed role in eradicating rats, possums and stoats.’’