Context. All over the world, invasive alien mammals present conservation problems. Feral horses are invasive in many countries and their management is challenging. Aims. To determine the demography of feral horses in Tornquist Park, Argentina, so as to develop a quantitative basis for their management. Methods. Ground counts of individually identified female horses were conducted monthly from 1995 to 1997 and from 2000 to 2002, and seasonally in 1998 and 1999. We calculated the age structure, foaling and survival rates of mares and analysed the effects of adult density and rainfall on demographic parameters. The population trend was calculated by fitting a logistic equation to annual adult mare counts. Key results. The foaling rate averaged 0.55 annually and the survival rate in females averaged 0.89 for adults, 0.91 for juveniles, 0.87 for yearlings and 0.94 for foals. We found adult density, rainfall and the previous year’s rainfall to have a significant effect on fecundity but no effect on adult, juvenile and foal female survival rates. Adult density had a significant negative effect on female yearling survival; however, the effect is probably trivial. The logistic equation parameters gave r = 0.327 and carrying capacity (K) = 240 adult mares. Conclusions. A density-dependent response is suggested. The population growth is mainly limited by low fecundity, with the reduced adult female survival probably also playing a minor role. Implications. It is expected that the present long-term demographic study will contribute to the understanding of feral ungulate ecology and improve the management of feral populations.

Feral invasive mammals challenge management strategies worldwide including the feral horse (Equus caballus) population in Tornquist Park, Argentina. In this study, I constructed population matrix models using demography data collected between 1995 and 2002. I validated the models with independent counts from 2008 to 2016. I individually identified feral horses and recorded them as I walked a fixed path that covered 20 km 2 . I performed an elasticity analysis to estimate the influence of the demographic parameters on population growth rate. In addition, I explored whether body condition score could be a proxy for carrying capacity. Model projections with the highest values of fecundity and survival exhibited by females of all ages during 1995-2002 fit the counts from 2008 to 2016, when growth rate was moderate (λ = 1.10), very well. Elasticity of adult female survival (0.54) was 4 times higher than for fecundity and survival of all other ages. Body condition of adult females at the end of winter, 2012-2013, after reductions in density, was improved compared with 2001-2002 when the population approached carrying capacity. The validated population model together with body condition score could allow managers to take more informed decisions when planning the control of feral horses in Tornquist Park. This approach could also be applied to other small, closed, feral horse populations and other large-mammal populations.

Invasive alien species (IAS) can act as vectors for the introduction of pathogens in ecosystems and their transmission to threatened native species (TNS), leading to biodiversity loss, population reductions and extinctions. We assessed pathogens potentially occurring in a set of IAS in the Southern Cone of South America and identified TNS potentially vulnerable to their effects. Also, we assessed how risk analysis systems proposed or adopted by national authorities in the study region value the importance of pathogens. We identified 324 pathogens in the selected IAS, which could potentially affect 202 TNS. Wild boar (Sus scrofa) was the IAS with the largest number of pathogens (91), followed by domestic dog (Canis familiaris) (62), red deer (Cervus elaphus) (58), rock dove (Columba livia) (37), American vison (Neovison vison) (18), European hare (Lepus europaeus) (17), common starling (Sturnus vulgaris) (12), common slider (Trachemys scripta) (6), and American bullfrog (Lithobates catesbeianus) (2). Most TNS were in the ''vulnerable'' IUCN category, followed by ''endangered'' and ''critically endangered'' species. Bacteria were the most frequently represented pathogens (112), followed by ectoparasites (78), viruses (69), protozoa and other (65). The direct effects of IAS on native wildlife are beginning to be addressed in South America, and their potential impact as pathogen spreaders to native wildlife has remained largely unexplored. Risk analysis systems associated with the introduction of IAS are scarce in this region. Although the existing systems contemplate hazard analyses for the co-introduction of pathogens, they underestimate the potential impact of diseases on TNS. Conservation efforts in the region would benefit from systems which give pathogen risk a relevant place, and from government agencies promoting targeted disease surveillance in IAS and wildlife.

El día 11 de septiembre de 2015 se desarrolló la mesa redonda “Invasión del estornino pinto (Sturnus vulgaris) en Argentina”, en el marco de la XVI Reunión Argentina de Ornitología organizada por la Sección Ornitología del Museo de La Plata (Facultad de Ciencias Naturales y Museo, Universidad Nacional de La Plata). En esa oportunidad se informó acerca de las características de la especie, de las consecuencias de su introducción en distintos países, del estado actual de la invasión en Argentina y de los antecedentes relacionados con su control. Además, se realizó una actividad en la que los participantes propusieron medidas de acción prioritarias para el manejo de la especie a nivel local, regional y nacional. En esta contribución resumimos los aspectos más relevantes de la reunión y las conclusiones de la misma.

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