Darwin’s finches treat their feathers with a natural repellent

Abstract

Darwin’s finches are highly innovative. Recently we recorded for the first time a behavioural innovation in Darwin’s finches outside the foraging context: individuals of four species rubbed leaves of the endemic tree Psidium galapageium on their feathers. We hypothesised that this behaviour serves to repel ectoparasites and tested the repellency of P. galapageium leaf extracts against parasites that negatively affect the fitness of Darwin’s finches, namely mosquitoes and the invasive hematophagous fly Philornis downsi. Mosquitoes transmit pathogens which have recently been introduced by humans and the larvae of the fly suck blood from nestlings and incubating females. Our experimental evidence demonstrates that P. galapageium leaf extracts repel both mosquitoes and adult P. downsi and also inhibit the growth of P. downsi larvae. It is therefore possible that finches use this plant to repel ectopoarasites.

Environmentally cued hatching in the bird‐parasitic nest fly Philornis downsi

“…Under this situation, first instars could either wait until nestlings hatch or feed on parent birds, as has already been demonstrated through the presence of anti-Philornis antibodies in brooding females (Huber et al, 2010;Koop et al, 2013b) and through the finding of P. downsi larvae and pupae in which eggs failed to hatch (Cimadom et al, 2016;Fessl et al, 2018). We suggest that increased larval longevity in Philornis may facilitate exploitation of ephemeral and unpredictable resources such as nestlings.…”

“…More specifically, extended lifespan in neonate larvae may facilitate oviposition in nests that contain host eggs but no nestlings. Under this situation, first instars could either wait until nestlings hatch or feed on parent birds, as has already been demonstrated through the presence of anti-Philornis antibodies in brooding females (Huber et al, 2010;Koop et al, 2013b) and through the finding of P. downsi larvae and pupae in which eggs failed to hatch (Cimadom et al, 2016;Fessl et al, 2018).…”

“…In various species of Darwin's finches in Gal apagos (Fessl et al, 2006) and in society finches in captivity (Bulgarella et al, 2017) the first instars feed within the nares or ears of nestling birds and feed externally on the body of nestlings in the second and third instars. There is some recent evidence from Darwin's finches that young P. downsi larvae can feed on brooding females as well (Huber et al, 2010;Koop et al, 2013b;Cimadom et al, 2016) but the dynamics of this behaviour are not well understood (Fessl et al, 2018). The development time of their nestling hosts (taking Darwin's finches as an example) ranges between 12 and 14 days (Fessl & Tebbich, 2002).…”

“…Philornis downsi fitness is presumably maximised by timing oviposition and hatching such that the complete development time of larvae can be completed on a brood of nestlings. There is some recent evidence from Darwin's finches that young P. downsi larvae can feed on brooding females as well (Huber et al, 2010;Koop et al, 2013b;Cimadom et al, 2016) but the dynamics of this behaviour are not well understood (Fessl et al, 2018).…”

Evidence for rapid downward fecundity selection in an ectoparasite (Philornis downsi) with earlier host mortality in Darwin’s finches

“…Previously, P. downsi larvae were only present in Darwin's finch nests once the host nestlings had hatched (Fessl & Tebbich, 2002;O'Connor et al, 2014). However, in recent years, there have been a growing number of observations of P. downsi larvae in nests during the incubation phase suggesting that larvae are feeding on incubating females (Cimadom et al, 2016;Common et al, 2019). Incubating female finches have been found to express P. downsi-specific antibodies (Huber et al, 2010), and females with higher antibody levels were found to have fewer parasites in their nest (Knutie et al, 2016;Koop, Owen, Knutie, Aguilar, & Clayton, 2013).…”