Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper)

Sonia Kleindorfer,Lauren K Common,Petra Sumasgutner

doi:10.3390/birds2040032

Sonia Kleindorfer, Lauren K Common + Show 1 more

Open Access

https://doi.org/10.3390/birds2040032

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Abstract

When different introduced species across trophic levels (parasite, predator) invade island systems, they may pose significant threats to nesting birds. In this study, we measure nesting height and infer causes of offspring mortality in the critically endangered Medium Tree Finch (Camarhynchus pauper), an island endemic restricted to Floreana Island on the Galápagos Archipelago. Considering all nests at which a male built a nest, sang and attempted to attract a female (n = 222 nests), only 10.4% of nests produced fledglings (5% of nests had total fledging success, 5.4% of nests had partial fledging success). Of the 123 nests chosen by a female, 18.7% produced fledglings and of 337 eggs laid, 13.4% produced fledglings. Pairing success was higher for older males, but male age did not predict nesting success. All nests with chicks were infested with avian vampire fly larvae (Philornis downsi). We attributed the cause of death to avian vampire fly if chicks were found dead in the nest with fly larvae or pupae (45%) present. We inferred avian (either Asio flammeus galapagoensis or Crotophaga ani) predation (24%) if the nest was empty but dishevelled; and black rat (Rattus rattus) predation (20%) if the nest was empty but undamaged. According to these criteria, the highest nests were depredated by avian predators, the lowest nests by rats, and intermediate nests failed because of avian vampire fly larvae. In conclusion, there is no safe nesting height on Floreana Island under current conditions of threats from two trophic levels (introduced parasitic dipteran, introduced mammalian/avian predators; with Galápagos Short-Eared Owls being the only native predator in the system).

Highlights

Introduction conditions of the Creative CommonsIslands occupy only 5.3% of the world’s surface, contain a disproportionate amount of biodiversity, and experience by far the greatest proportion of species extinction and extinction risk [1], mostly due to invasive species [2,3]
The human-induced extinction rate is high for island birds [13]
The critically endangered Medium Tree Finch (C. pauper) is an island endemic restricted to Floreana Island, Galápagos Archipelago

Summary

Introduction

Introduction conditions of the Creative CommonsIslands occupy only 5.3% of the world’s surface, contain a disproportionate amount of biodiversity, and experience by far the greatest proportion of species extinction and extinction risk [1], mostly due to invasive species [2,3]. Birds 2021, 2 high levels of endemism and few predators and parasites compared with the mainland source population [4,5], and have inspired natural history theory [6,7,8,9]. These systems are currently challenged by combinations of introduced species [10], why many endemic island species are increasingly the focus of conservation efforts [11,12]. We lack understanding into the combined effects of multiple introduced species at different trophic levels, such as parasite and predator, on avian nesting success

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