Eco-ethological characterisation of the alien species vinous-throated parrotbill (Paradoxornis webbianus) and evaluation of its effects on indigenous species.

The phenomenon of exotic species (or alien) species introduction is increased in the last few years, closely connected to the increment in human activities on the global scale. In spite of the high number of introduced organisms, only few of them succeed in establishing a new range and become naturalised, that is establish self-sustaining populations. Then, only a small part of naturalised species can become an invasive species and a threat to biological diversity. There are many reasons inducing a demographic explosion of these species, in particular the lack of limiting factors such as competitors and predators presence and also the introduced species characteristics, themselves such as population growth rate, or migratory strategy can cause invasiveness.\nThe impact and cost of biological invasions are global and enormous, in both ecological (for example native species extinction, ecosystem alteration) and economic terms. In fact, biological invasions are the second threat to biodiversity after habitat destruction. \nParrotbills (Paradoxornis webbianus), Chinese Passeriformes, were introduced in Varese Province, north-western Italy, in 1995 by an animal trader that introduced 150 animals. In the same year these birds were found in Brabbia Marsh Natural Reserve, on southern side of Lake Varese.\nThe expansion of this species has been confirmed from frequent sightings since 2003 in other province areas, like Lake Comabbio, Besozzo and Bagnoli Valley, south-east of Brabbia Marsh.\nFollowing the major international nature protection directive exhortations we carried out a multiple scale approach to study genetics and auto-ecology of this species and to understand its impact on indigenous species. In particular, the aims of this project were: to define the present species distribution, to develop knowledge on parrotbill auto-ecology, and to evaluate the potential competition with other species, evaluating parrotbill invasiveness.\nWe carried out 5 censuses from February 2006 to February 2008, to establish species expansion that reconfirmed the 2003 presence areas. Moreover, the area occupied by parrotbills presents several ecological corridors that can lead to an eventual future expansion. \nParrotbill were caught using mist-nets during bird ringing seasons in the Brabbia Marsh Ornithological Station. During the bird ringing operations we caught once 367 animals and 318 other animal were instead caught more than one time, for a total of 685 animals caught. \nNumber of caught parrotbills varied during the years, following meteorological events: in fact, population decreased after winters with high snow abundance. Using the Schnabel and the Burnham and Overton methods we calculated population size estimates. The two methods gave different results, in particular the Burnham and Overton method overrated population estimate if compared with Schnabel, but we can estimate a population between 350 to 3500 animals in Brabbia Marsh reserve.\nWe monitored 19 animals during different periods of the year with radio tracking technique using tags (BD-2N, Holohil Ltd, Ontario, Canada) weighing 0.43 g. Home range dimensions vary from less than an hectare (0.2-1.3 ha) in the reproductive season, to 35 hectares (20- 35 ha) in winter season, with intermediate situations during autumn, when dimension range was wider (9.5-47.5 ha). Differences in home range dimensions were statistically significant (ANOVA F (2,16) =8.9291 P= 0.003) and moreover this result is in accordance to the home range dimensions registered in the area of origin.\nTo analyse habitats present in the home range we used two different methods, in particular Compositional Analysis and Ivlev’s electivity index. In both cases emerged that parrotbills prefer wetland areas, in particular grey willow shrub, marsh areas.\nTo study parrotbills environmental perception in terms of scale we used program FRACTAL to analyse movement patterns derived from radio tracking data. The analysis of variance shows that the parrotbill spatial perception increases with scale (ANOVA F(1,476)=247.65 P<0.001) and changes with seasons (ANOVA F(2,475)=8.3953 P=0.0003). These results indicate that the potential dispersal season is during autumn, when parrotbills show a broader spatial scale perception.\nTo understand species auto-ecology we analysed parrotbills diet using faecal samples collected during the ringing bird sessions. Diet composition changes during the year, in particular proportion of vegetal items increased from spring to winter (ANOVA F(3,174) =142.77 P<0.001). Diet is composed in particular by Ichneumonidae, Chrysomeloidea, Carabidae, Scarabaeoidea and Araneidae. The vegetable part is composed by ate elder (Sambucus nigra), pokeweeds (Phytolacca sp.) and seeds of common reed (Phragmites australis). \nWe also compared the parrotbills diet with trophic spectra of 10 indigenous species using the Proportional Similarity Index the Pianka’s Overlap Index. Both methods gave similar results, the parrotbill diet resulting similar to the diet of all species considered, and the most similar \nspecies resulted are the reed warbler (Acrocephalus scirpaceus) (PSI: 0.43; OI:0.61) and the reed bunting (Emberiza schoeniclus) (PSI: 0.34; OI:0.52). \nSpecies invasiveness was estimated according to the “Risk assessment models for establishment of exotic vertebrates in Australia and New Zealand”. Considering all factors of this decision support model, the parrotbill invasivity risk is classified as Serious, in accordance to the Vertebrate Pest Committee of Australia.\nAll these results, connected with other species characteristics (generalism, large geographic original range, monogamy, monomorphic, social foraging, and non migratory strategy) suggest that the parrotbill, even if it is not yet an invasive species in our zone, could become a pest in the future.

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