Additive negative effects of Philornis nest parasitism on small and declining Neotropical bird populations

Abstract

SummaryThe declining-population paradigm holds that small populations are particularly vulnerable to anthropogenic influences such as habitat destruction, pollution and species introductions. While the effects of particular stressors, such as parasitism, may be unimportant in a large, healthy population, they can be serious and even devastating in situations characterised by a restricted geographic range, or by fragmented or reduced population sizes. We apply this idea to nest parasitism of threatened Neotropical bird species that exist in small populations, focusing on dipteran nest parasites in the genusPhilornis. We review the literature onPhilornisparasitism exerting negative pressure on bird populations that have become small and isolated due to human actions and present a new case ofPhilornisparasitism of a threatened hummingbird species. Our aim is to raise awareness about the exacerbating effect that nest parasites can have on small and declining bird populations; especially when biological information is scarce. The five reviewed cases involve two species of Darwin’s Finches in the Galápagos Islands attacked by the invasiveP. downsi, two species of hawks on islands in the Caribbean attacked by the nativeP. piciandP. obscura, and the Yellow CardinalGubernatrix cristatain southern South America attacked by an unknownPhilornisspecies. We also present new documentation of parasitism of a threatened hummingbird species in mainland Ecuador by an unidentifiedPhilornisspecies. We recommend more field studies to determine the presence of nest parasites in bird populations worldwide to improve understanding how nest parasites affect bird fitness and population viability and to allow time to act in advance if needed. Parasitism byPhilornismay represent a severe mortality factor in most already threatened bird species, putting them at greater risk of extinction. Therefore, parasitism management should be included in all threatened species recovery plans.

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

“…The human-induced extinction rate is particularly high for island birds [13]. New predators and/or parasites rapidly diminish naïve prey on islands [11,14,15], either because of adult mortality or low nesting recruitment. Yet, we lack understanding into the combined effects of multiple introduced species at different trophic levels, such as parasite and predator, on avian nesting success.…”

Sub-lethal effects of permethrin exposure on a passerine: implications for managing ectoparasites in wild bird nests

“…For some threatened bird species, the management of parasites is an essential component of recovery plans because of their impact on reproductive success ( Bulgarella et al , 2019 ). For example, in the Dominican Republic, nest parasitism by the fly Philornis pici is a contributing factor to the decline of the critically endangered Ridgway’s hawk ( Buteo ridgwayi ; BirdLife International, 2018 ; Hayes et al ., 2019 ).…”

A roadmap to identifying and filling shortfalls in Neotropical ornithology

“…Knowing the critical importance of these interspecies interactions, both local and widespread, we must wonder at how many additional examples await discovery within Neotropical bird communities. Work on parasites and their impacts on Neotropical bird populations, especially in the context of global change are even more limited but are now known to be potentially extremely important at least in insular systems (Bulgarella et al 2018).…”