title: Invasive parasites, habitat change and heavy rainfall reduce breeding success in Darwin's finches.
abstract: Invasive alien parasites and pathogens are a growing threat to biodiversity worldwide, which can contribute to the extinction of endemic species. On the Galápagos Islands, the invasive parasitic fly Philornis downsi poses a major threat to the endemic avifauna. Here, we investigated the influence of this parasite on the breeding success of two Darwin's finch species, the warbler finch (Certhidea olivacea) and the sympatric small tree finch (Camarhynchus parvulus), on Santa Cruz Island in 2010 and 2012. While the population of the small tree finch appeared to be stable, the warbler finch has experienced a dramatic decline in population size on Santa Cruz Island since 1997. We aimed to identify whether warbler finches are particularly vulnerable during different stages of the breeding cycle. Contrary to our prediction, breeding success was lower in the small tree finch than in the warbler finch. In both species P. downsi had a strong negative impact on breeding success and our data suggest that heavy rain events also lowered the fledging success. On the one hand parents might be less efficient in compensating their chicks' energy loss due to parasitism as they might be less efficient in foraging on days of heavy rain. On the other hand, intense rainfalls might lead to increased humidity and more rapid cooling of the nests. In the case of the warbler finch we found that the control of invasive plant species with herbicides had a significant additive negative impact on the breeding success. It is very likely that the availability of insects (i.e. food abundance)is lower in such controlled areas, as herbicide usage led to the removal of the entire understory. Predation seems to be a minor factor in brood loss.
authors.affiliation: Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Arno
authors.initials: A
authors.lastname: Cimadom
authors.affiliation: Charles Darwin Foundation, Puerto Ayora, Santa Cruz Island, Galápagos, Ecuador.
authors.forename: Angel
authors.initials: A
authors.lastname: Ulloa
authors.affiliation: Institute for Science and Technology, Klosterneuburg, Austria.
authors.forename: Patrick
authors.initials: P
authors.lastname: Meidl
authors.affiliation: Department of Zoology, University of Cambridge, Cambridge, United Kingdom.
authors.forename: Markus
authors.initials: M
authors.lastname: Zöttl
authors.affiliation: Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Elisabet
authors.initials: E
authors.lastname: Zöttl
authors.affiliation: Charles Darwin Foundation, Puerto Ayora, Santa Cruz Island, Galápagos, Ecuador.
authors.forename: Birgit
authors.initials: B
authors.lastname: Fessl
authors.affiliation: BirdLife Austria, Vienna, Austria.
authors.forename: Erwin
authors.initials: E
authors.lastname: Nemeth
authors.affiliation: BirdLife Austria, Vienna, Austria.
authors.forename: Michael
authors.initials: M
authors.lastname: Dvorak
authors.affiliation: Charles Darwin Foundation, Puerto Ayora, Santa Cruz Island, Galápagos, Ecuador.
authors.forename: Francesca
authors.initials: F
authors.lastname: Cunninghame
authors.affiliation: Department of Behavioural Biology, University of Vienna, Vienna, Austria.
authors.forename: Sabine
authors.initials: S
authors.lastname: Tebbich
mesh_terms: D000818:Animals; D001947:Breeding; D017753:Ecosystem; D004484:Ecuador; D005260:Female; D046369:Finches / Q000145:classification / Q000254:growth & development* / Q000469:parasitology*; D006540:Herbicides / Q000494:pharmacology; D008018:Life Cycle Stages / Q000187:drug effects; D008297:Male; D009117:Muscidae / Q000187:drug effects / Q000502:physiology*; D011157:Population Dynamics; D011235:Predatory Behavior; D011891:Rain; D012307:Risk Factors
chemical_list: D006540:Herbicides