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The monk parakeet (Myiopsitta monachus) is a South American species unique among parrots; it builds communal stick nests that allow independence from tree or cliff cavities required by most parrots. As a very successful invasive species, it has expanded into several countries around the world. Questions remain around the factors that allowed this species to be such a successful invader in its native range as in other countries, and particularly the extent that evolutionary processes may be involved in adapting to new areas. Along with this line of analysis, we focused on assessing whether morphological characteristics are sufficiently heritable, and therefore responsive to selection. As the first step in this direction, we have estimated heritability of monk parakeet in six external morphological traits considered of potential adaptability value. Samples were obtained in the province of Córdoba in central Argentina. Data from seven microsatellites were used to determine the familial relationships among individuals. Heritabilities and genetic correlations were estimated by means of animal models. We found evidence for significant heritability in the six traits measured, particularly in weight, tarsus length and bill width. We also found evidence of maternal effects on morphological traits, particularly in the traits with lower heritability: wing length, bill length and tail length. Genetic correlations between traits were significant and associated with phenotypic correlations, suggesting that these traits are constrained in terms of evolutionary potential, whereas the amount of additive genetic variance in weight, tarsus length and bill width indicate that these traits could be responsive to selection.

Aim: Effective policy and management responses to the multiple threats posed by invasive alien species (IAS) rely on the ability to assess their impacts before conclusive empirical evidence is available. A plethora of different IAS risk and/or impact assessment protocols have been proposed, but it remains unclear whether, how and why the outcomes of such assessment protocols may differ. Location: Europe. Methods: Here, we present an in-depth evaluation and informed assessment of the consistency of four prominent protocols for assessing IAS impacts (ElCAT, GISS, Harmonia⁺ and NNRA), using two non-native parrots in Europe: the widespread ring-necked parakeet (Psittacula krameri) and the rapidly spreading monk parakeet (Myiopsitta monachus). Results: Our findings show that the procedures used to assess impacts may influence assessment outcomes. We find that robust IAS prioritization can be obtained by assessing species based on their most severe documented impacts, as all protocols yield consistent outcomes across impact categories. Additive impact scoring offers complementary, more subtle information that may be especially relevant for guiding management decisions regarding already established invasive alien species. Such management decisions will also strongly benefit from consensus approaches that reduce disagreement between experts, fostering the uptake of scientific advice into policy-making decisions. Main conclusions: Invasive alien species assessments should take advantage of the capacity of consensus assessments to consolidate discussion and agreement between experts. Our results suggest that decision-makers could use the assessment protocol most fit for their purpose, on the condition they apply a precautionary approach by considering the most severe impacts only. We also recommend that screening for high-impact IAS should be performed on a more robust basis than current ad hoc practices, at least using the easiest assessment protocols and reporting confidence scores.

Over 40 species of parrots, members of order Psittaciformes, have established nonnative populations globally. Monk parakeets (Myiopsitta monachus) are among the most invasive bird species worldwide. In their introduced range, populations of monk parakeets have caused negative impacts on native species, habitats, economies, and human safety. Lethal population management has been complicated by the intelligence of monk parakeets, as they quickly alter behavior to avoid risks. Further, lethal control programs have been halted due to public controversy, as parakeets are highly charismatic. The contraceptive DiazaCon has been demonstrated to effectively reduce fertility in monk parakeets and other psittacines. In field applications, chemical control agents (e.g., toxicants and contraceptives) must be delivered in a manner that prohibits access by nontarget species. We developed and tested a parakeet-selective feeder. The feeder allows access by parakeets and limits access by nontarget bird species by lowering a wire exclusion curtain around the feeder, requiring a zygodactyl toe arrangement to access food. We tested the parakeet-selective feeder in trials with captive and freeranging monk parakeets and nontarget species in Florida, USA. Monk parakeets successfully accessed food from the parakeet-selective feeder throughout the study. The mean number of daily feeder uses by nontarget species decreased from a high of nearly 16 uses per day when the exclusion curtain was not implemented to < 1 use per day when implemented. Our findings suggest the parakeet-selective feeder is a promising tool for delivery of bait treated with chemical control agents to manage monk parakeets and other nonnative parakeet populations, but implementation success will likely vary by target species, location, local faunal diversity, and availability of alternative forage.

Due to their large population sizes, synanthropic birds, including native and invasive species, can transmit pathogens to other vertebrates, and even humans. In particular, Newcastle disease virus (NDV) can cause lethal infections in a wide range of avian species as well as mild infections in humans and other non-avian hosts. In this study conducted in Barcelona, Spain, we assessed the seroprevalence of NDV in three synanthropic species comprising one native species (feral pigeon, Columba livia var. domestica ; N = 16) and two invasive parrots (monk parakeet, Myiopsitta monachus , N = 50; and rose-ringed parakeet, Psittacula krameri , N = 23). These species are considered to have played important roles in the introduction and spread of NDV due to their high population densities, gregariousness, and prolonged viral shedding through faeces. We found a high seroprevalence of NDV in the feral pigeon (56%) and monk parakeet (38%) but a low seroprevalence in the rose-ringed parakeet (4%). These differences may be explained by the frequent interactions among feral pigeons and monk parakeets in their daily lives facilitating viral transmission from the former to the latter, because the feral pigeon is a well-known NDV reservoir. By contrast, the low seroprevalence of NDV in rose-ringed parakeets could be explained by its less frequent contacts with other urban bird species. The high seroprevalence of NDV in feral pigeons and monk parakeets provides new insights into the roles of novel interspecific relationships in the transmission and spread of NDV, and the risk of these synanthropic species as a source of NDV in urban environments. Finally, our findings highlight the need to monitor NDV in both native and non-native birds to prevent its spread to poultry, wildlife, and humans.

Invasive alien species are a growing threat to biodiversity, and identifying the mechanisms that enable these species to establish viable populations in their new environment is paramount for management of the problems they pose. Using an unusually large number of both failed and successful documented introductions of parakeets (Aves: Psittacidae) in Europe, we test two of the major hypotheses on the establishment success of invading species, namely the climate-matching and the human-activity hypothesis. European human population centres where ring-necked parakeet (Psittacula krameri) and/or monk parakeet (Myiopsitta monachus) introductions have occurred. Data on ring-necked and monk parakeet introductions in Europe were gathered from various sources, including published books and articles, but also from unpublished reports and local grey literature. Information was verified with experts from the region under consideration. In order to test the climate-matching hypothesis, we verified whether the climatic factors that determine the parakeets' native ranges also explain establishment success in Europe. Parakeet occurrence data from the native ranges were analysed using the presence-only modelling method M axent, and correlations between parakeet establishment and climatic and anthropogenic variables in Europe were assessed using both stepwise logistic regression and the information-theoretic model selection approach. The establishment success of ring-necked and monk parakeets was found to be positively associated with human population density, and, both in the native and in the introduced regions, parakeet occurrence was negatively correlated with the number of frost days. Thus, parakeets are more likely to establish in warmer and human-dominated areas. The large number of independent parakeet introductions in Europe allows us to test the often-used climate-matching and human-activity hypotheses at the species level. We show that both hypotheses offer insight into the invasion process of monk and ring-necked parakeets. Our results suggest that, in the future, parakeet establishment probability may increase even further because global warming is likely to cause a decrease in the number of frost days and because urbanization and human populations are still increasing.

Background Non-native species are often introduced in cities, where they take advantage of microclimatic conditions, resources provided by humans, and competitor/predator release to establish and proliferate. However, native communities in the surrounding rural or natural areas usually halt their spread through biotic resistance, mainly via top-down regulative processes (predation pressure). Here, we show an unusual commensal interaction between exotic and native bird species that favours the spread of the former from urban to rural habitats. Results We show how Monk parakeets Myiopsitta monachus , an invasive species often introduced in cities worldwide, associated for breeding with a much larger, native species (the white stork Ciconia ciconia ) to reduce predation risk in central Spain, thus allowing their colonization of rural areas. Parakeets selected stork nests close to conspecifics and where breeding raptors were less abundant. Parakeets always flushed when raptors approached their nests when breeding alone, but stayed at their nests when breeding in association with storks. Moreover, when storks abandoned a nest, parakeets abandoned it in the following year, suggesting that storks actually confer protection against predators. Conclusions Our results show how a protective-nesting association between invasive and native species can counteract biotic resistance to allow the spread of an invasive species across non-urban habitats, where they may become crop pests. Monk parakeet populations are now growing exponentially in several cities in several Mediterranean countries, where they coexist with white storks. Therefore, management plans should consider this risk of spread into rural areas and favour native predators as potential biological controllers.

Biological invasions are widely recognised as a significant threat to biodiversity, a driver of global change and a relevant economic problem. Actions to control or eradicate invasive alien species (IAS) can cause great controversy, especially when targeted species are charismatic. Thus, better understanding people’s perceptions of invasive species is key for ensuring more effective IAS management. The ring-necked parakeet (Psittacula krameri) and the monk parakeet (Myiopsitta monachus) are two of the most successful avian invaders worldwide, causing several ecological and socio-economic impacts in recipient regions. We used image-based questionnaires to assess differences in people’s perceptions of recently established ring-necked and monk parakeet colonies in an urban environment (Porto, Portugal). Most participants recognised both species and had a positive perception of the parakeets, with respondents’ education, gender and age influencing their perception. Potential ecological, economic and social impacts caused by these species do not seem be widely acknowledged yet, likely due to the limited awareness of IAS or the incipiency of their impacts in the area. Our results suggest future actions to manage feral parakeet populations in the area will likely be met with public opposition. While increased public literacy about IAS might help improve risk awareness, complementary tools should be used to promote support for potential interventions. Social assessments are vital to identify, evaluate and address social costs and benefits of IAS. Further research should adopt a multidisciplinary approach to foster communication in IAS management actions, implementing effective and sustainable measures to tackle biological invasions by charismatic vertebrates.

The psittacine beak and feather disease (PBFD) is a globally widespread infectious bird disease that mainly affects species within the Order Psittaciformes (parrots and allies). The disease is caused by an avian circovirus (the beak and feather disease virus, BFDV), which is highly infectious and can lead to severe consequences in wild and captive populations during an outbreak. Both legal and illegal trading have spread the BFDV around the world, although little is known about its prevalence in invasive parrot populations. Here, we analyze the BFDV prevalence in sympatric invasive populations of rose-ringed (Psittacula krameri) and monk parakeets (Myiopsitta monachus) in Southern Spain. We PCR-screened 110 blood samples (55 individuals from each species) for BFDV and characterized the genotypes of five positives from each species. About 33% of rose-ringed parakeets and 37% of monk parakeets sampled were positive for BFDV, while neither species showed disease symptoms. The circovirus identified is a novel BFDV genotype common to both species, similar to the BFDV genotypes detected in several parrot species kept in captivity in Saudi Arabia, South Africa and China. Our data evidences the importance of an accurate evaluation of avian diseases in wild populations, since invasive parrots may be bringing BFDV without showing any visually detectable clinical sign. Further research on the BFDV prevalence and transmission (individual–individual, captive–wild and wild–captive) in different bird orders and countries is crucial to understand the dynamics of the viral infection and minimize its impact in captive and wild populations.

The monk parakeet (Myiopsitta monachus) is an invasive species introduced in Chile during the early seventies and now abundant in several areas of Santiago metropolis. For most of our knowledge, there are no genetic studies focused on the invasion of monk parakeets in Chile. The current study aims to assess the levels of population structure in monk parakeets from different municipalities in Santiago through next generation sequencing. Genetic material was obtained from pectoral muscle collected from monk parakeet fledglings (n = 204) sampled in Santiago, Chile. Using Double digest, restriction-site associated DNA (ddRADseq), 102,834 loci and 3195 SNPs were identified, allowing a high-resolution study in a population with little genetic diversity explained by an invasive founder effect. Genetic structure was modeled using the fixation index, STRUCTURE, and principal component analyses. Results showed low levels of genetic structure in the monk parakeet population from Santiago, evidencing high genetic flow between all studied municipalities. However, slight differences were observed when parakeets from the northern areas of Santiago were compared to those from the rest of the city. The geography of the city might explain these differences; with a small succession of hills of up to 400 m, potentially in-part isolating a northern reproductive colony. It is also possible that this northern population originated from or bred with a different release event or a combination of these factors. This study represents the first genetic characterization of monk parakeets in Chile and provides a high-resolution model to study recent invasion processes.

While most of the knowledge on invasive species focuses on their impacts, little is known about their potential positive effects on other species. Invasive ecosystem engineers can disrupt recipient environments; however, they may also facilitate access to novel resources for native species. The monk parakeet (Myiopsitta monachus) is a worldwide invader and the only parrot that builds its own communal nests, which can be used by other species. However, the ecological effects of these interspecific interactions are barely known. We compared the role of the monk parakeet as a nest-site facilitator in different rural and urban areas, both invaded and native, across three continents and eight breeding seasons. A total of 2690 nests from 42 tenant species, mostly cavity-nesting birds, were recorded in 26% of 2595 monk parakeet nests. Rural and invaded areas showed the highest abundance and richness of tenant species. Multispecies communal nests triggered interspecific aggression between the monk parakeet host and its tenants, but also a cooperative defense against predators. Despite the positive effects for native species, monk parakeets also facilitate nesting opportunities to other non-native species and may also transmit diseases to tenants, highlighting the complexity of biotic interactions in biological invasions.