What is threatening the Wilkins' Finch?

The Wilkins' Finch (Nesopiza wilkinsi) is an olive-yellow songbird endemic to Nightingale Island, located in the remote archipelago, Tristan da Cunha in the South Atlantic. The bird is classed as critically endangers by the IUCN red list with an estimated population of 49 in the wild in 2021.

The birds spend the majority of their lives in the forest, feasting on fruit and seeds from Phylicia trees. They occasionally forage for insects in tussocks grass and fern-bush but this is not a sustainable primary food source.

Phylicia arborea is an evergreen shrub with a notable silver underside and needle-like leaves. It once flourished on the island providing the birds with the perfect habitat for foraging, breeding and sheltering.

However, an invasive scale insect was introduced to the Island by humans which feeds on these trees and secretes honeydew in its waste. Honeydew encourages mould growth which eventually hinders photosynthesis causing the tree to die causing major ecosystem stress.

Additionally, the Island experienced intense storms throughout 2019 which destroyed 80% of the forest resulting in habitat degradation and major ecosystem fluctuations. The extreme weather and scale insects caused the Wilkins' Finches to drop from 120 to just 20 breeding pairs over the next two years.

The birds only lay 1-2 eggs and have a relatively short breeding season between November and January, making it hard to quickly recover to a stable population. The eggs and juveniles are often predated on by the Tristan Thrush and habitat destruction caused by the scale insects has reduced nesting success even further.

What are we doing to help?

The RSPB are working alongside the centre for agriculture and bioscience international, FERA and the Nightingales government to combat the killer scale insects. In April, 2021 scientists released a parasitic wasp, Microterys nieteri onto the Island which kill the scale insects.

The wasps are orange-brownish on colour and around 4mm in size. They lay their eggs inside the host which kills it and allows for their offspring to emerge later. Since this ingenious introduction has began, there has been a population increase of 40-70 breeding pairs of Wilkins' Finches as of February this year.

Forest regrowth has been enhanced by conservationists by creating a tree nursery for Phylicia on the Island in order to recover biosecurity whilst the pests are being mitigated. It will take some time before the forest is restored to a state of healthy diversity but the Finch population seems to be following an upward trajectory.

Success in the past

Biocontrol is a form of pest, weed or disease prevention using natural organisms to deter a target species. Microterys nieteri is an invertebrate biocontrol agent or macrobial; itself and many other parasitoids have been used in agriculture in the past.

For example in New South Wales, Australia, farmers are placing capsules of parasitic wasp eggs as an alternative to expensive and environmentally damaging pesticides to mitigate silverleaf whitefly. Biocontrol is not only effective in conservation but is acting as a sustainable pest control method in the agricultural sector.