Plant invasion causes alterations in Darwin's finch feeding patterns in Galapagos cloud forests

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 Darwin's finches. We posit that food web disturbances caused by invasive Rubus niveus (blackberry), have contributed to the rapid decline of the insectivourous green warbler finch (Certhidae olivacea). We compared the birds' dietary changes in long-term management, short-term management and unmanaged areas. We measured C:N ratios, and & delta;15N-nitrogen and & delta;13C-carbon values in both consumer tissues (bird-blood) and food sources (arthropods), as indicators of resource use change, and collected mass abundance, and arthropod diversity data. We characterised the birds' diets using isotope mixing models. The results revealed that finches in (blackberry-invaded) unmanaged areas foraged more on abundant, yet lower quality, arthropods present in the invaded understory. This suggests that blackberry encroachment leads to a decrease in food source quality with physiological consequences for green warbler finch chicks. Results also implied that blackberry control has a short-term impact on food source quantity, which led to a decrease in chick recruitment that we observed in our previous studies; despite this, in the long-term, these managed systems show signs of recovery within three years of restoration.

Automated summary

Invasive species, especially the blackberry plant, pose a significant threat to forest biodiversity, particularly on islands like the Galapagos. This study examines the impact of blackberry invasion on the decline of the green warbler finch, a unique species found in the cloud forest. The study compares the dietary changes of the finches in managed and unmanaged areas, and the results indicate that blackberry encroachment leads to a decrease in food source quality and quantity, resulting in a decline in chick recruitment.