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

String pulling and discrimination learning in jackdaws (Corvus monedula) and New Caledonian crows (Corvus moneduloides)

Ziel der ersten Studie war es, die Herangehensweise von Dohlen (Corvus monedula) und Neukaledonischen Krähen (Corvus moneduloides) beim Lösen von physikalischen Problemen zu untersuchen. Die Fähigkeit eine Schnur hochzuziehen, um an die Belohnung zu kommen (string pulling genannt), ist ein klassisches Beispiel von Problemlösung bei Vögeln. Diese Aufgabe erfordert die Koordination von Schnabel und Fuß. Die Dohlen hatten kaum Probleme den erforderlichen Bewegungsablauf auszuführen; jedoch verbesserte sich im Laufe der Versuchsdurchgänge die Latenzzeit bis zum Start des string pulling Verhaltens eher graduell. Im Gegensatz dazu hatten die Neukaledonischen Krähen größere Probleme den erforderlichen Bewegungsablauf auszuführen, die Latenzzeit bis zum Start des string pulling verbesserte sich aber sprunghaft nach 4-5 Versuchsdurchgängen. Insgesamt war aber nur ca. die Hälfte der Individuen je Art erfolgreich. Die Ergebnisse werden in Bezug auf den Einfluss von angeborenen Verhaltensweisen, operanter Konditionierung und Verständnis über Ziel-Mittel-Beziehungen („means-end understanding“) diskutiert. In der zweiten Studie wurde das Diskriminationslernen bei Dohlen in drei verschiedenen Sinnesmodalitäten (visuell, akustisch und Gewicht) untersucht. Alle drei Aufgaben wurden im Kontext von string pulling durchgeführt, deshalb mussten die Individuen an beiden Schnüren ziehen, um das Diskriminationsmerkmal wahrnehmen zu können. Die Ergebnisse zeigten, dass die Dohlen spontan begannen von einer Schnur zur anderen zu wechseln, bevor sie sich für eine entschieden (aktive Informationssuche), und dass sie in der Lage sind Objekte allein anhand ihres Gewichts zu unterscheiden. Obwohl der Versuchsaufbau das Potenzial hat, eine Standardmethode in der vergleichenden Kognitionsforschung in den Bereichen Diskriminationslernen und Wahrnehmung von Kausalzusammenhängen zu werden, sind die Ergebnisse zum Teil dürftig und mögliche Gründe dafür werden diskutiert.The aim of the first study was to investigate physical problem solving in jackdaws (Corvus monedula) and New Caledonian crows (Corvus moneduloides). The ability to retrieve a reward by pulling up a string is a classic example of problem solving in birds, which requires well co-ordinated and repeated actions of pulling up the string and stepping on the string. The jackdaws had fewer problems performing the required motor pattern once they stepped on the pulled up string, but the latency to start with string pulling decreased more gradually from trial to trial. In contrast, the New Caledonian crows had greater difficulties performing the required motor pattern of pull-stepping, but after 4-5 trials the latency of first pull-step showed a sudden decrease. However, only about half of the individuals in both species managed to solve the task. The results are discussed in respect to facilitating innate behavioural components, operant conditioning and means-end understanding. In the second study jackdaws’ discrimination ability in three sensory modalities (visual, acoustic, weight) was tested. The whole setup was put in the context of string pulling, thus the subjects were required to pull the strings in order to gain access to the discriminatory features in all three tasks. The results showed that jackdaws spontaneously adopted the crucial method of switching from one string to the other before making their choice (information seeking) and that jackdaws seem to be able to discriminate two objects solely on the basis of weight. Although the experimental setup has the potential of becoming a standard method for comparative research in discrimination learning and causal reasoning, the performance of the birds is poor overall and possible reasons for this are discussed

Invasive parasites, habitat change and heavy rainfall reduces breeding success in Darwin’s finches

Invasive eingeschleppte Krankheitserreger und Parasiten stellen weltweit eine immer größer werdende Bedrohung der Biodiversität dar. Sie können massiv zur Ausrottung von gefährdeten endemischen Arten beitragen. Die invasive parasitische Fliege Philornis downsi und andere eingeschleppte Prädatoren bedrohen die endemische Vogelwelt der Galapagos Inseln. In dieser Studie untersuchten wir den Einfluss dieser eingeschleppten Arten auf den Bruterfolg zweier Darwin Finken, dem Laubsängerfink (Certhidea olivacea) und dem Kleinen Baumfink (Camarhynchus parvulus). Die Population des Laubsängerfinken auf der Insel Santa Cruz ist in den letzten 15 Jahren um mehr als die Hälfte geschrumpft, wohingegen die Population des Kleinen Baumfinken mehr oder weniger stabil blieb. Ziel der Studie war es, zu untersuchen, ob der Laubsängerfink im Verglich zum Kleinen Baumfink während des Brutgeschäfts besonders sensibel auf verschiedene potentielle Stressfaktoren reagiert. Des Weiteren wollten wir feststellen, ob der niedrige Bruterfolg bedingt durch Parasiten und Prädatoren zum rapiden Rückgang dieser Art beiträgt. Der eingeschleppte Parasit Philornis downsi hatte einen negativen Einfluss auf den Bruterfolg beider untersuchten Vogelarten. Der Prädationsdruck war relativ gering. Unsere Daten weisen ebenfalls darauf hin, dass extreme Wetterbedingungen, wie Starkregenereignisse, und der Einsatz von Herbiziden zur Bekämpfung von invasiven Pflanzenarten sich zusätzlich negativ auf den Bruterfolg beider Darwin Finken auswirkten. Wir vermuten, dass beide Faktoren die Nahrungsverfügbarkeit während der Jungenaufzucht negativ beeinflussen, was die Mortalität der bereits durch Parasiten geschwächten Küken erhöht. Die jährlichen Schwankungen von Starkregen während der Brutsaison würden auch das unterschiedliche Ausmaß von P. downsi auf das Wachstum und die Mortalität der Jungen in vorherigen Studien erklären. Unsere Daten stützen die Hypothese, dass der geringe Bruterfolg zum Populationsrückgang beim Laubsängerfink und Kleinen Baumfink beiträgt. Zähldaten für den Kleinen Baumfink zeigen auch bei dieser Art einen Abwärtstrend in den letzten Jahren, sowie eine Veränderung in der Altersstruktur mit einer Zunahme von älteren Vögeln, was für einen geringeren Reproduktionserfolg spricht.Invasive alien parasites and pathogens are a major and growing threat to biodiversity worldwide, which can significantly contribute to the extinction of vulnerable endemic species. On the Galápagos Islands, the invasive parasite Philornis downsi and other introduced predators pose a precarious threat to endemic bird species. Here, we investigated the influence of these invasive species on the breeding success of two endemic Darwin’s finches: the warbler finch (Certhidea olivacea) and the sympatric small tree finch (Camarhynchus parvulus). The warbler finch has experienced a dramatic decline in population size, dropping by over 50% in the last 15 years on Santa Cruz Island, while the small tree finch has remained stable over the last decade. To address this differing population development, we aimed to identify whether warbler finches, in comparison with small tree finches, are particularly vulnerable during the breeding cycle, and if so, to look which stages were most affected. Furthermore, we wanted to determine whether low breeding success caused by parasites and predators contributed to the rapid decline of this species. We found that the introduced parasite Philornis downsi had a high negative influence on breeding success in both the arboreal finches. Our data does, however, suggest that extreme climatic conditions, such as heavy rain and control of invasive plant species with herbicides, may have an important additive negative impact on both species. We assume that these factors influence food supply during chick rearing, which in turn results in mortality in chicks that are already weakened by parasitism. The yearly variation in heavy rainfall during the breeding season may also explain the different magnitudes of Philornis effect on chick growth and mortality found in previous studies. Our data support the hypothesis that low breeding success leads to population decline in the warbler finch as well as in the small tree finch. For the latter species, counting data show a less stable population over the last few years, as well as an apparent change in age structure, with a higher prevalence of older birds suggesting low reproduction

Population dynamics of an invasive bird parasite, Philornis downsi (Diptera: Muscidae), in the Galapagos Islands.

The invasive parasitic fly, Philornis downsi (Muscidae), is one of the greatest threats to the avifauna of the Galapagos Islands. The larvae of this fly feed on the blood and tissues of developing nestlings of at least 18 endemic and native birds. The aim of the current study was to investigate biotic and abiotic factors that may influence the population dynamics of this invasive parasite. To study the influence of vegetation zone and related climatic factors on fly numbers, a bi-weekly monitoring program using papaya-baited traps was carried out at a dry, lowland site and at a humid, highland site on Santa Cruz Island between 2012-2014. Female flies, a large proportion of which were inseminated and gravid, were collected throughout the year at both sites, indicating females were active during and between the bird breeding seasons. This is the first evidence that female flies are able to persist even when hosts are scarce. On the other hand, catch rates of male flies declined between bird breeding seasons. Overall, catch rates of P. downsi were higher in the drier, lowland habitat, which may be a consequence of host or resource availability. Time was a stronger predictor of adult fly numbers than climate, further suggesting that P. downsi does not appear to be limited by its environment, but rather by host availability. Seasonal catch rates suggested that populations in both habitats were continuous and multivoltine. Numbers of adult female flies appeared to be regulated chiefly by simple direct density dependence, and may be governed by availability of bird nests with nestlings. Nevertheless, confounding factors such as the existence of reservoir hosts that perpetuate fly populations and changes in behavior of P. downsi may increase the vulnerability of bird hosts that are already IUCN red-listed or in decline

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

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

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

<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