Molecular characterisation of haemoparasites in forest birds from Robinson Crusoe Island: Is the Austral Thrush a potential threat to endemic birds?

SummaryThe Juan Fernández Firecrown Sephanoides fernandensis and Juan Fernández Tit-Tyrant Anairetes fernandezianus are two endemic forest birds inhabiting Robinson Crusoe Island and are classified as ‘Critically Endangered’ and ‘Near Threatened’ respectively by IUCN. Previous research concluded that the two main factors involved in the decline of these birds were habitat degradation and the introduction of predator / competitor species. However, the potential role of parasitic diseases has not yet been explored. In order to explore hypothetical host-switching phenomena, we genetically identified the haemoparasites present in four bird species, the two endemic species mentioned above and two recent colonisers, Green-Backed Firecrown Sephanoides sephaniodes and Austral Thrush Turdus falcklandii. We failed to find infections by different blood parasites (Plasmodium, Haemoproteus, Leucocytozoon, Trypanosoma, Babesia and Isospora) in the endangered Juan Fernández Firecrown. However, the Juan Fernández Tit-Tyrant was infected with some parasites shared with the Austral Thrush. The latter species may function as a key-host species on the island as it showed both the higher hemoparaasitic diversity and prevalence. The role of Green-Backed Firecrowns is apparently of lower importance because only one individual was found parasitized. The Austral Thrush could be responsible of the introduction of some parasites also isolated from the Juan Fernández Tit-Tyrant and represent a potential threat to the endemic firecrown due to its role as a reservoir. The spread of Austral Thrushes could increase the contact between species, increasing the probability of a switching event.

Conservation of the Juan Fernandez firecrown and its island habitat

The Juan Fernandez Islands constitute two distantly separated (182 km) major islands, of which Isla Robinson Crusoe is the closest (667 km) to the Chilean mainland, and a number of smaller surrounding islets. The endemic Juan Fernandez firecrown Sephanoides fernandensis once inhabited both major islands and numbered many thousands. Today it exists only on Isla Robinson Crusoe and numbers just a few hundred. Another hummingbird, the green-backed firecrown S. sephaniodes, inhabits this island but also occurs on the mainland. The islands are in ecological meltdown as a result of the removal of much of the native (largely endemic) biota. This degradation has been exacerbated by introduced herbivorous and carnivorous mammals, which are extirpating all that remains. In a previous investigation the authors assessed the evolutionary relationships and genetic variation in the Juan Fernandez firecrown population. They showed that the species: (i) is a relative of the high Andean hummingbirds; (ii) is a close sister species of the green-backed firecrown; (iii) dispersed to the islands approximately 0.5–1 million years ago, unlike the green-backed firecrown, which is probably a very recent invader; (iv) maintains some genetic variation, although significantly lower than that found in the green-backed firecrown island population. Because of their relatively recent divergence the authors aimed to find out if the two species compete for resources. In addition, they assessed the conservation options for the Juan Fernandez firecrown and provided recommendations for its management. They concluded that the survival of the Juan Fernandez firecrown is inextricably linked to the holistic restoration of ecosystem/ community function of the island. The initial step must involve the removal of introduced mammals, followed by replanting of native flora. Although the authors do not support the use of captive propagation as a general conservation tool, they believe that, because the Juan Fernandez firecrown is composed of only one small population that is under extreme threat of extinction, a captive population should be established.