Invasive parasites habitat change and heavy rainfall reduce breeding success in Darwin's finches

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

Dual parasitism of Fork-tailed Drongos by African and Jacobin Cuckoos §

Different species of brood parasitic birds, which lay their eggs in the nests of host foster-parents, rarely target the same host species population. We report brood parasitism of Fork-tailed Drongos Dicrurus adsimilis in the southern Kalahari Desert by both African Cuckoo Cuculus gularis and Jacobin Cuckoo Clamator jacobinus serratus. Drongos are the only known host for the African Cuckoo, and were more frequently parasitised by this species (21.8% nests). Nevertheless, parasitism rates suggest that in the Kalahari, drongos are also an important host for Jacobin Cuckoo (4.6% nests). Jacobin Cuckoos likely compete with African Cuckoos for drongo hosts, as exemplified by the occurrence of both African and Jacobin Cuckoo eggs in the same drongo clutch. The drongo’s defensive adaptations to parasitism by African Cuckoos, including egg rejection, may also curtail parasitism by Jacobin Cuckoos. The extent of competition between these cuckoo species and whether they possess adaptations to prevent one another’s access to drongo hosts remains to be explored.Keywords: alloxenia, brood parasitism, coevolution, host selection, offspring competitio

Effect of herbicide use on the breeding success of warbler finches.

<p>Percentage of successful warbler finch nests in areas with no control measures by the National Park (2010: n = 14, 2012: n = 32) and in areas where the National Park recently sprayed herbicides to control the invasive <i>Rubus niveus</i> (2010: n = 12, 2012: n = 42). Numbers above bars indicate total numbers of cases.</p

Age of chicks at brood loss.

<p>Percentage of nests with total brood loss depending on the chicks' age. Warbler finch (n = 21), small tree finch (n = 31). Total brood loss included the following types of nesting failures: dead chicks in the nest, empty nest and predated nests. Numbers above bars indicate total numbers of cases.</p

<i>Philornis downsi</i> intensity in warbler finch and small tree finch nests.

<p>Mean (± SD) number of <i>P. downsi</i> specimens (larvae, pupae and puparia) per nest of the breeding season 2012 of warbler finches and small tree finches for all nests with chicks (warbler finch n = 44, small tree finch n = 38), nests with chicks of six days and younger (warbler finch n = 11, small tree finch n = 20) and nests with chicks of seven days and older (warbler finch n = 33, small tree finch n = 18).</p

Variables that explained variation in breeding success of warbler finches and small tree finches in 2012 by GLMs with a binomial error structure.

<p>Significant variables are marked in bold.</p><p>Variables that explained variation in breeding success of warbler finches and small tree finches in 2012 by GLMs with a binomial error structure.</p

Breeding success and types of nesting failure.

<p>Proportional nesting outcome for the breeding season 2010 (A) and 2012 (B) of warbler finch nests and small tree finch nests of the <i>Scalesia</i> zone population on Santa Cruz, Galápagos. Numbers above bars indicate total numbers of cases.</p

Population trends of warbler finches and small tree finches.

<p>Mean (± SD) number of singing warbler finch males and small tree finch males per point count in the <i>Scalesia</i> zone on Santa Cruz, Galápagos, for the years 1997, 1998, 2008, 2010 (data from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0107518#pone.0107518-Dvorak1" target="_blank">[27]</a>), 2004 and 2005 (Dvorak et al. unpublished data) and 2012.</p

Invasive Parasites, Habitat Change and Heavy Rainfall Reduce Breeding Success in Darwin's Finches

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