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

1
College of Science and Engineering, Flinders University, Adelaide 5001, Australia
2
Konrad Lorenz Research Center, Core Facility for Behavior and Cognition and Department of Behavioral and Cognitive Biology, University of Vienna, 4645 Grünau im Almtal, Austria
*
Author to whom correspondence should be addressed.
Academic Editor: Jukka Jokimäki
Birds 2021, 2(4), 427-444; https://doi.org/10.3390/birds2040032
Received: 15 September 2021 / Revised: 1 December 2021 / Accepted: 2 December 2021 / Published: 4 December 2021
(This article belongs to the Special Issue Feature Papers of Birds 2021)
Invasive species on islands pose high risk to endemic flora and fauna unable to defend themselves. In this study, we measure the effects of introduced predators and the parasitic Avian Vampire Fly on nesting success in the critically endangered Medium Tree Finch on Floreana Island in the Galapagos archipelago. Only 10.4% of nests produced young, and the rest were killed by either predators or parasites. The lowest nests were primarily depredated by rats, the highest nests had evidence for predation by birds, and nestlings at the intermediate nest height were killed by parasitic fly larvae. In conclusion, confronted by introduced mammalian and avian predators and parasitic flies, there is no safe nesting height for this critically endangered species, and nesting success is far too low to sustain the population. Control measures are urgently needed to save Darwin’s finches from extinction.
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). View Full-Text
Keywords: Rattus rattus; Philornis downsi; Short-eared Owl; Smooth-billed Ani; avian predators; invasive species; nest condition; Galápagos Archipelago; Floreana Island; conservation management Rattus rattus; Philornis downsi; Short-eared Owl; Smooth-billed Ani; avian predators; invasive species; nest condition; Galápagos Archipelago; Floreana Island; conservation management
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MDPI and ACS Style

Kleindorfer, S.; Common, L.K.; Sumasgutner, P. Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper). Birds 2021, 2, 427-444. https://doi.org/10.3390/birds2040032

AMA Style

Kleindorfer S, Common LK, Sumasgutner P. Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper). Birds. 2021; 2(4):427-444. https://doi.org/10.3390/birds2040032

Chicago/Turabian Style

Kleindorfer, Sonia, Lauren K. Common, and Petra Sumasgutner. 2021. "Nesting Success and Nesting Height in the Critically Endangered Medium Tree Finch (Camarhynchus pauper)" Birds 2, no. 4: 427-444. https://doi.org/10.3390/birds2040032

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