Evidence of hidden hunger in Darwin's finches as a result of non-native species invasion of the Galapagos cloud forest

Abstract

Invasive species pose a major threat to forest biodiversity, particularly on islands, such as the Galapagos. Here, invasive plants are threatening the remnants of the unique cloud forest and its iconic Darwins finches. We posit that food web disturbances caused by invasive Rubus niveus (blackberry), but also the management measures used to control it, could contribute to the rapid decline of the insectivourous warbler finch (Certhidae olivacea). We compared changes in long-term management, short-term management and unmanaged areas. We measured C:N ratios, {delta}15N-nitrogen and {delta}13C-carbon signatures in bird blood and arthropods, as indicators of resource use change, in addition to mass abundance and diversity of arthropods. We reconstructed the birds diets using isotope mixing models. The results revealed that finches in (Rubus-invaded) unmanaged areas foraged on abundant yet low quality arthropods and had shorter tarsi. Is this the first evidence of hidden hunger in degraded terrestrial ecosystems in Galapagos?