Invasive ring-necked parakeets Psittacula krameri in Belgium: habitat selection and impact on native birds

There is a large and growing number of alien species in ecosystems all over the world. In view of this, management efforts should concentrate on invasives that have detrimental effects on native biota. However, action against invasives is often hindered by a lack of relevant ecological information such as the expected distribution and impact of the invader. Our aims were to identify the habitat characteristics that influence ring-necked parakeet abundance in Belgium and to assess the effects of competition for nesting cavities with native hole-nesters. We determined the abundance of parakeets and native hole-nesters in 44 study sites using point counts. We examined the relationship between parakeet numbers and a set of habitat and landscape variables and to assess the effect of competition, we studied the relationships between the number of parakeets and the number of native hole-nesters. We found that parakeet abundance differs between vegetation types based on dominant tree species, and that abundance is higher in forests or parks surrounded by built-up areas. Parakeet numbers were also strongly associated with cavity density, suggesting that this may be a limiting factor. Of the two native hole-nesters considered to be the most vulnerable to competition (nuthatch and starling), we found a negative association with parakeet numbers for the nuthatch only. No relations were found with starlings or any of the other hole-nesting species examined. These findings should be considered in the debate concerning the possible need of action against this species.     

Interference competition between an invasive parakeet and native bird species at feeding sites

Interference competition has proved to be a factor of successful establishment of invasive species. This type of competition may have a stronger impact when native species have temporal niche overlap with the invasive species. The ring-necked parakeet Psittacula krameri has been successfully introduced in many countries and its interspecific agonistic behavior has already been reported. The purpose of this study is to analyze the territorial and preemptive interference competition between the ring-necked parakeet and native bird species in a recently colonized area. We used an empirical approach by recording video sequences in gardens equipped with bird feeders in winter. Our results showed that the ring-necked parakeet was the most frequent species at the feeders. Several native species showed temporal niche overlap with the ring-necked parakeet, the highest overlap being with the starling Sturnus vulgaris. The starling was also the species most impacted by interference competition with the parakeet. Our study suggests that, by being most frequently present at the feeders, by demonstrating the most agonistic behavior and by hindering access to food of the other species, the ring-necked parakeet is a superior competitor and may compete with native bird species.     

Comparative ecology of sympatric orange-fronted parakeets (

Sympatric orange-fronted (Cyanoramphus malherbi) and yellow-crowned parakeets (C. auriceps) were surveyed in a South Island beech (Nothofagusspp.) forest during the spring and summer of 1998/99. Habitat use, behaviour and diet were recorded for each parakeet identified. A single observer did all recording. Both species were seen most frequently in the upper-most 20% of the forest stratum. Orange-fronted parakeets were seen more frequently than yellow-crowned parakeets in the lowest 20% of the forest stratum. Orange-fronted parakeets were seen calling less frequently and comforting more frequently than yellow-crowned parakeets, and this may reflect a difference in breeding period behaviour. Both species were usually seen feeding. In summer, both species were seen feeding mostly on seeds, predominantly from mountain beech — but this was a beech mast year. The spring diet of both species appeared to be largely flowers and invertebrates. Orange-fronted parakeets were seen feeding on flowers less frequently and on invertebrates more frequently than yellow-crowned parakeets. We suggest factors that may have contributed to the decline in abundance of both species: (1) greater competition between the two species in a habitat substantially modified by humans; (2) competition with introduced finch species; (3) competition with wasps for invertebrates; and (4) vulnerability to introduced predators. These last two factors are likely to affect orange-fronted parakeets in particular, because they appear to feed more on invertebrates and make greater use of the ground and low-growing plants.     

Genetic analysis of interspecific hybridisation in the world’s only Forbes’ parakeet (Cyanoramphus forbesi) natural population

Genetic introgression from Chatham Island Red-crowned parakeet (Cyanoramphus novaezelandiae chathamensis) is a long-standing problem in the conservation of the rare Forbes’ parakeet (C. forbesi) on Mangere Island, New Zealand. Microsatellite genotypes, mitochondrial DNA sequences, and morphological markers have been applied to study the situation. An extensive history of hybridisation was detected in the single remaining Forbes’ parakeet population, where no less than 81% of all birds screened are considered hybrids. Genetic markers showed that a large proportion of birds identified as Forbes’ parakeets by crown plumage are cryptic hybrids. Only a small proportion of birds with Forbes’ parakeet morphotype were found to be genetically distinct from Chatham Island Red-crowned parakeets using microsatellite and mitochondrial DNA assignment tests, but these still represent an Evolutionarily Significant Unit (ESU) for conservation.     

Rapid morphological changes,admixture and invasive success in populations of Ring-necked parakeets (<Emphasis Type="Italic">Psittacula krameri</Emphasis>) established in Europe

The Ring-necked parakeet (Psittacula krameri), native of Asia and Africa, is a very successful invasive species in Europe: it has been present there for over 50 years. A recent study showed that European invasive populations occupy a colder climatic niche than in their native range but the establishment of this tropical species in temperate regions remains unexplained. Two main hypotheses may explain the success of Ring-necked parakeet in Europe: admixture between individuals from different origins and/or rapid adaptation to new environmental conditions. In this study, we investigated with molecular data the origin of European populations of Ring-necked parakeets to assess whether these populations result from admixture between individuals from different source populations. We also investigated the morphology of individuals from European populations and from the native range to assess whether the invasive populations have morphologically diverged from their source and could have become adapted to European conditions. We found evidence of admixture in some of the European populations but not all of them. Admixture between individuals from different origins within European populations thus cannot explain alone their invasive success. Conversely, we found that the morphology of the individuals from European populations has diverged from the morphology of native individuals, in a similar direction. Rapid adaptation to European environmental conditions via phenotypic plasticity or natural selection could thus be a factor explaining the invasive success of Ring-necked parakeets in Europe.     

Identification methods and deterministic factors of owl roadkill hotspot locations in Mediterranean landscapes

Road fatalities are among the major causes of mortality for Strigiformes species and may affect the population’s survival. The use of mitigation strategies must be considered to overcome this problem. However, because mitigation along the total length of all roads is not financially feasible, the locations where Strigiformes roadkills are more frequent (i.e., road fatality hotspots) must be identified. In addition to hotspot identification, factors that influence the occurrence of such fatalities should be recognized to allow mitigation measures to be delineated. We used road fatality data collected from 311 km of southern Portugal roads over a 2-year period to compare the performance of five hotspot identification methods: binary logistic regression (BLR), ecological niche factor analysis (ENFA), Kernel density estimation, nearest neighbor hierarchical clustering (NNHC), and Malo’s method. BLR and ENFA modelling were also used for recognizing roadkill deterministic factors. Our results suggest that Malo’s method should be preferred for hotspot identification. The main factors driving owl roadkillings are those associated with good habitat conditions for species occurrence and specific conditions that promote hunting behavior near roads. Based on these factors, several mitigation measures are recommended.     

Assessing <Emphasis Type="Italic">Octopus vulgaris</Emphasis> distribution using presence-only model methods

The distribution of the common octopus (Octopus vulgaris) in the Mediterranean and Eastern Atlantic waters is evaluated using two presence-only analyses: The maximum entropy model (Maxent) and the ecological niche factor analysis (ENFA). Maxent predicts those geographical areas that satisfy the environmental or abiotic requirements of a species while ENFA explores the niche and habitat preferences of O. vulgaris. The analyses were implemented recovering the spatial information from 213 octopus presence data collected from surveys and bibliographical records. Together, these analyses provided reasonable estimates of the species distribution and the octopus habitat. Among the gathered set of explanatory environmental variables, sea bottom temperature, sea bottom salinity, surface dissolved oxygen and sea surface chlorophyll-α appear as the main variables involved in O. vulgaris distribution. These results were confronted with the available literature.     

Nest habitat selection by the Austral parakeet in north‐western Patagonia

Identifying habitat or nesting microhabitat variables associated with high levels of nest success is important to understand nest site preferences and bird–habitat relationships. Little is known about cavity availability and nest site requirements of cavity nesters in southern hemisphere temperate forests, although nest site limitation is suggested. Here we ask which characteristics are selected by the Austral parakeet (Enicognathus ferrugineus) for nesting in Araucaria araucana–Nothofagus pumilio forest in Argentine Patagonia. We compared nest plot and tree characteristics with unused plots and trees among areas of different A. araucana–N. pumilio density. We also examine whether nest plot and tree use and selection, and the associated consequences for fitness of Austral parakeets are spatially related to forest composition. Austral parakeets showed selectivity for nests at different spatial scales, consistently choosing isolated live and large trees with particular nest features in a non‐random way from available cavities. Mixed A. araucana–N. pumilio forests are ideal habitat for the Austral parakeets of northern Patagonia, offering numerous potential cavities, mainly in N. pumilio. We argue that Austral parakeet reproduction and fitness is currently very unlikely to be limited by cavity availability, although this situation may be rapidly changing. Natural and human disturbances are modifying south temperate forests with even‐aged mid‐successional stands replacing old growth forests. Cavity nesting species use and need old growth forests, due to the abundance of cavities in large trees and the abundance of larvae in old wood. Neither of the latter resources is sufficiently abundant in mid‐successional forests, increasing the vulnerability and threatening the survival of the Austral.     

Landscape-scale evaluation of habitat uses by sympatric mammals foraging for bark and buds in a heavy snowfall area of northern Japan

This study focused on influences of three different growing populations of mammals foraging for bark and buds—Japanese serows (Capricornis crispus), Tohoku hares (Lepus brachyurus angustidens), and Japanese macaques (Macaca fuscata)—on a cool-temperate forest in northern Japan. To acquire the initial knowledge to facilitate ecological monitoring of the influences, we evaluated habitat uses by each species on a landscape scale by using ecological niche factor analysis (ENFA), and identified commonalities and differences among the uses by using discriminant analysis (DA). Within a 50-km² area, we selected five 5-km transects and recorded tracks of each mammal on the snow surface along transects during the month of March in 2008 and 2009. The track data were used as the proof of species presence for entry into ENFA and DA. Marginality and specialization of species habitat use, computed by ENFA, indicated that the macaque habitat represented the most heterogeneous distribution and the lowest environmental tolerance, which was strictly limited by altitude and terrain conditions to prevent exposure to severe cold climate conditions. This refuge selection by macaques resulted in habitat segregation from serows, although it appears that both mammals prefer the same young broadleaf forests. Meanwhile, the serow was observed to be distinctly inclined to use mountainous forests and to avoid artificial environments. As a result, its habitat could be differentiated from that of the hare, as confirmed by coefficients of a discriminant factor. These findings indicate that the impact of three different mammals foraging on the native vegetation could be quite restrictive.     

Establishment success of invasive ring‐necked and monk parakeets in Europe

Aim 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. Location European human population centres where ring‐necked parakeet (Psittacula krameri) and/or monk parakeet (Myiopsitta monachus) introductions have occurred. Methods 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 Maxent , 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. Results 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. Main conclusions 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.     

Reproductive timing as a constraint on invasion success in the Ring-necked parakeet (<Emphasis Type="Italic">Psittacula krameri</Emphasis>)

Climate similarity favors biological invasion, but a match between seasonality in the novel range and the timing of life cycle events of the invader also influences the outcome of species introduction. Yet, phenology effects on invasion success have generally been neglected. Here we study whether a phenological mismatch limits the non-native range of a globally successful invader, the Ring-necked parakeet, in Europe. Given the latitudes at which parakeets have established across Europe, they breed earlier than expected based on breeding dates from the native Asian range. Moreover, comparing the breeding dates of European populations to those of parakeets in the native Asian range, to five native breeding bird species in Europe and to the start of the growing season of four native European trees shows that the discrepancy between expected and actual breeding phenology is greater in northern Europe. In northern European populations, this temporal mismatch appears to have negative effects on hatching success, and on population growth rates in years that are colder than average in the first six months. Phenological mismatch also can explain why parakeets from African populations (that are more likely to breed in autumn) have been poor invaders compared to parakeets from Asia. These lines of evidence support the hypothesis that the reproductive phenology of the Ring-necked parakeet can be a limiting factor for establishment and range expansion in colder climates. Our results provide growing support for the hypothesis that the match between climate seasonality and timing of reproduction (or other important life cycle events) can affect the establishment success, invasive potential and distribution range of introduced non-native species, beyond the mere effect of climate similarity.     

Ecological niche modeling of the sympatric giant and red pandas on a mountain-range scale

Habitat use and separation between the two sympatric species, the giant panda and the red panda, have been primary causes of coexistence at the fine scale. In this paper, we addressed the question of coexistence between species in space. By Ecological Niche Factor Analysis, we calculated species-specific habitat requirements, built habitat suitability maps and examined interspecific differences in spatial niche parameters. According to the ENFA scores, suitable habitats in the giant and red panda are surrounded by high-altitude, and are rich in conifer forest. Compared with the giant panda, however, the red panda rather preferred sparse forests, and normally colonized far from village and road. Despite similar narrow niche breadth for both pandas, difference of niche overlap indices implied that the width of environmental niche of red pandas almost completely encompasses that of the giant panda. We, therefore, suggest that differences in use of ecological niche variables may contribute to coexistence of the sympatric species in space. Based on highly suitable locations of the sympatric species maps, most official reserves appear to be poorly located or are too small, and new reserves are recommended to be established in the central part of core habitats in the Liangshan Mountains.     

A general framework for the statistical exploration of the ecological niche

We propose a new statistical framework for the exploratory analysis of the ecological niche, the “General niche-environment system factor analysis” (GNESFA). The data required for this analysis are (i) a table giving the values of the environmental variables in each environment unit (EU, e.g., the patches of habitat on a vector map), (ii) a set of weights measuring the availability of the EUs to the species (e.g., the proportion of the study area covered by a given patch), and (iii) a set of utilization weights describing the use of the EUs by the focal species (e.g., the proportion of detections of the species in each patch). Each row of the table corresponds to a point in the multidimensional space defined by the environmental variables, and each point is associated with two weights. The GNESFA searches the directions in this space where the two weight distributions differ the most, choosing one distribution as the reference, and the other one as the focus. The choice of the utilization as the reference corresponds to the MADIFA (Mahalanobis distances factor analysis), which identifies the directions on which the available EUs are in average the furthest from the optimum of the niche, allowing habitat suitability modelling. The choice of the availability as the reference corresponds to the FANTER (Factor analysis of the niche, taking the environment as the reference), which identifies the directions on which the niche is the furthest from the average environment (marginality) and those on which the niche is the narrowest compared with the environment (specialization). The commonly used ENFA (Ecological niche factor analysis) is at the middle point between the MADIFA and the FANTER, considering both distributions as the reference and the focus simultaneously. When used concurrently, these three analyses allow an extensive exploration of the system.     

An isotopic technique to mark mid-sized vertebrates non-invasively

Understanding the basis of habitat choice having important implications for explaining the distribution of organisms, as well as helping to differentiate between habitats of different quality for effective management. In this study, the effects of sex, age and reproductive status on habitat use patterns of cheetahs Acinonyx jubatus in the Serengeti plains were explored using Ecological Niche Factor Analysis (ENFA). Our results showed that gender and territoriality did not affect patterns of habitat use. However, females tended to be more specialized when they were young than when they were older, displaying a more restricted ecological niche. Likewise, older females without cubs were more specialized than the same adult females with young cubs. This result did not hold for younger females. Altogether, the ENFA approach allowed us to (1) use the large amount of incidental sighting data collected over 12 years on cheetah spatial distribution; (2) identify the importance of reproductive status and age on the relationship between animals and their habitat; (3) further demonstrate that ENFA is applicable in a wide range of situations, including for exploring individual variation in niche definition.     

Dynamic species distribution models reveal spatiotemporal habitat shifts in native range‐expanding versus non‐native invasive birds in an urban area

Urbanisation as a major driver of changes leads to the extinction of some species while others increase in abundance, especially non‐native species. Spatiotemporal distribution patterns of these successful species are likely to be shaped by their response and tolerance to urban features. This study assesses the anthropo‐ecological requirements of two co‐occurring bird species, the native range‐shifting jackdaw Corvus monedula and the non‐native invasive ring‐necked parakeet Psittacula krameri. We built yearly models over an eight‐year period using an ensemble modelling approach assessing response differences through time and between species. Predictors describing human‐made structures, socio‐ecological proxies and resources availability were extracted from temporally coincident databases. Dispersal and habitat constraints were implemented in final models to provide more realistic forecasts of species future distributions. Ensemble models evaluated with a random partition of the training dataset showed a higher accuracy than those evaluated with an independent dataset from another time period. Our results highlight temporal variations in the relative importance of predictors for both studied species. Single‐season occurrence data may thus be insufficient to characterize species ecological requirements. The ring‐necked parakeet and the jackdaw showed different responses to urban features. Jackdaws preferred the more urbanized part of the city while the distribution of parakeets was strongly positively associated with the density of exotic ornamental trees. We concluded that ring‐necked parakeet range expansion is likely to be driven by its effective ability to exploit urban resources which native species do not or under exploit, suggesting an open window of foraging opportunities. However, the jackdaw may be misled by a high cavity availability and a large amount of low‐quality anthropogenic food in the urban core. We suggest that dynamic SDMs are a critical tool not only to forecast the future expansion of invasive species but also for a better understanding of processes driving urban biodiversity persistence.     

Presence-absence versus presence-only modelling methods for predicting bird habitat suitability

Habitat suitability models can be generated using methods requiring information on species presence or species presence and absence. Knowledge of the predictive performance of such methods becomes a critical issue to establish their optimal scope of application for mapping current species distributions under different constraints. Here, we use breeding bird atlas data in Catalonia as a working example and attempt to analyse the relative performance of two methods: the Ecological Niche factor Analysis (ENFA) using presence data only and Generalised Linear Models (GLM) using presence/absence data. Models were run on a set of forest species with similar habitat requirements, but with varying occurrence rates (prevalence) and niche positions (marginality). Our results support the idea that GLM predictions are more accurate than those obtained with ENFA. This was particularly true when species were using available habitats proportionally to their suitability, making absence data reliable and useful to enhance model calibration. Species marginality in niche space was also correlated to predictive accuracy, i.e. species with less restricted ecological requirements were modelled less accurately than species with more restricted requirements. This pattern was irrespective of the method employed. Models for wide‐ranging and tolerant species were more sensitive to absence data, suggesting that presence/absence methods may be particularly important for predicting distributions of this type of species. We conclude that modellers should consider that species ecological characteristics are critical in determining the accuracy of models and that it is difficult to predict generalist species distributions accurately and this is independent of the method used. Being based on distinct approaches regarding adjustment to data and data quality, habitat distribution modelling methods cover different application areas, making it difficult to identify one that should be universally applicable. Our results suggest however, that if absence data is available, methods using this information should be preferably used in most situations.     

Modelling habitat-suitability using museum collections: an example with three sympatric Apodemus species from the Alps

Aim, Location Although the alpine mouse Apodemus alpicola has been given species status since 1989, no distribution map has ever been constructed for this endemic alpine rodent in Switzerland. Based on redetermined museum material and using the Ecological-Niche Factor Analysis (ENFA), habitat-suitability maps were computed for A. alpicola , and also for the co-occurring A. flavicollis and A. sylvaticus .
Methods In the particular case of habitat suitability models, classical approaches (GLMs, GAMs, discriminant analysis, etc.) generally require presence and absence data. The presence records provided by museums can clearly give useful information about species distribution and ecology and have already been used for knowledge-based mapping. In this paper, we apply the ENFA which requires only presence data, to build a habitat-suitability map of three species of Apodemus on the basis of museum skull collections.
Results Interspecific niche comparisons showed that A. alpicola is very specialized concerning habitat selection, meaning that its habitat differs unequivocally from the average conditions in Switzerland, while both A. flavicollis and A. sylvaticus could be considered as 'generalists' in the study area.
Main conclusions Although an adequate sampling design is the best way to collect ecological data for predictive modelling, this is a time and money consuming process and there are cases where time is simply not available, as for instance with endangered species conservation. On the other hand, museums, herbariums and other similar institutions are treasuring huge presence data sets. By applying the ENFA to such data it is possible to rapidly construct a habitat suitability model. The ENFA method not only provides two key measurements regarding the niche of a species (i.e. marginality and specialization), but also has ecological meaning, and allows the scientist to compare directly the niches of different species.     

Foraging ecology of the red-crowned parakeet (

The diet of red-crowned parakeets (Cyanoramphus novaezelandiae novaezelandiae) and yellow-crowned parakeets (C. auriceps auriceps) was compared on Little Barrier Island, New Zealand between 1986 and 1987. Significant dietary differences were observed in these sympatric, congeneric species. Yellow-crowned parakeets ate significantly more invertebrates than red-crowned parakeets, which fed on a greater variety of plant foods. Red- crowned parakeets were found in all vegetation types depending on the availability of food and were commonly seen foraging on the ground in open habitats. In contrast, yellow-crowned parakeets were more arboreal and showed distinct preferences for forested habitats. The existence of both parakeet species in sympatry is examined as is the ecological importance of invertebrate food sources. Observed differences in the behaviour and ecology of parakeet species on Little Barrier Island are used to provide insight into the present day distribution and status of parakeets on mainland New Zealand.