1. Due to reductions in winter food resources, newly sown cereal seeds have become a key component of many bird species' diets, but these seeds are often treated with pesticides that may cause toxic effects. To complete an appropriate risk assessment, data on treated seed toxicity need to be combined with information about the risk of exposure of birds in the field and the factors that modulate such exposure. 2. We studied the abundance of pesticide-treated seeds available for birds in the field, the pesticides and their concentrations in treated seeds, and the bird species observed in the field that were feeding on these pesticide-treated seeds. The exposure of red-legged partridge to treated winter cereal seeds was characterized through the analysis of crop and gizzard contents of hunted individuals (n = 189). Moreover, we measured the contribution of cereal seeds in the autumn-winter diet of partridges in order to assess the potential risk of exposure to pesticide-treated seeds. 3. Density of treated seeds on the soil surface after sowing (11Á3 AE 1Á2 seeds m À2 in the centre of field and 43Á4 AE 5Á5 seeds m À2 in the headlands) was enough to provide, in an area between 6 and 50 m 2 , doses of six active ingredients above those indicating acute (i.e. a dose capable of killing 50% of individuals of a sensitive species) and / or chronic (no observed effect level) toxicity. 4. Up to 30 bird species were observed consuming treated cereal seeds in recently sown fields. Corn bunting was identified as an appropriate focal passerine species for the risk assessment of pesticide-treated seeds. 5. We found that treated seeds were an important route of pesticide ingestion for red-legged partridge; pesticide residues (six fungicides and two insecticides) were found in 32Á3% of crops and gizzards. Cereal seeds represented more than half (53Á4 AE 4Á3%) of total biomass consumed by partridges from October to February. 6. Synthesis and applications. The field exposure data combined with previous studies about the toxicity to partridges of using pesticide-treated seeds point to an unacceptable risk of this practice to farmland birds. Our results suggest that the prophylactic use of pesticide-coated seeds should be avoided, with the approval of this treatment considered on a case-by-case basis and accompanied with specific measures to minimize risks of adverse effects on avian communities.
Avian botulism kills thousands of waterbirds every year, including endangered species, but information about the differences between species in vulnerability to botulism outbreaks and the capacity to act as carriers of Clostridium botulinum is still poorly known. Here, we estimated the vulnerability to botulism of 11 waterbird species from Mediterranean wetlands by comparing the number of affected birds with the census of individuals at risk. The capacity of different species to act as carriers was studied by detecting the presence of the C. botulinum type C/D botulinum neurotoxin (BoNT) gene in fecal samples and prey items of waterbirds in the wild and by the serial sampling of cloacal swabs of birds affected by botulism. We found differences among species in their vulnerabilities to botulism, probably related to feeding habits, season of arrival, turnover, and, possibly, phylogenetic resilience. The globally endangered white-headed duck (Oxyura leucocephala) showed mortality rates in the studied outbreaks of 7% and 17% of the maximum census, which highlights botulism as a risk factor for the conservation of the species. Invasive water snails, such as Physa acuta, may be important drivers in botulism epidemiology, because 30% of samples tested positive for the BoNT gene during outbreaks. Finally, our results show that birds may excrete the pathogen for up to 7 days, and some individuals can do it for longer periods. Rails and ducks excreted C. botulinum more often and for longer times than gulls, which could be related to their digestive physiology (i.e., cecum development). IMPORTANCEBotulism is an important cause of mortality in waterbirds, including some endangered species. The global climate change may have consequences in the ecology of wetlands that favor the occurrence of botulism outbreaks. Here, we offer some information to understand the ecology of this disease that can be useful to cope with these global changes in the future. We have found that some species (i.e., coots and dabbling ducks) are more vulnerable to botulism and have a more relevant role in the onset and amplification of the outbreaks than other species (i.e., flamingos and grebes). Feeding habits can explain these differences in part; in addition to the well-known role of necrophagous fly maggots, we found here that water snails are frequent carriers of Clostridium botulinum. This is relevant, because these water snails can thrive in eutrophic and polluted wetlands, exacerbating other changes driven by climate change in wetlands.A vian botulism is an intoxication characterized by a severe flaccid paralysis of the muscles and final death by respiratory failure caused by the botulinum neurotoxins (BoNTs) produced by different types of Clostridium botulinum (1). There are 7 types of BoNT single toxins, plus their mosaics (with characteristics of two toxins), and each one affects different animal species and/or humans. In particular, avian botulism outbreaks in freshwater waterbirds are generally caused by the mosaic type C/D (2, 3...
Mediterranean wetlands show remarkable seasonal and annual variations in their hydroperiod, i.e. the period of time during which the wetland is inundated. Climate change-induced hydroperiod reductions have been shown to affect marshland birds but more studies are needed to understand this process in Mediterranean wetlands. The present study shows the demographic response of the Common Reed-warbler Acrocephalus scirpaceus to an unusual and prolonged drought in the Tablas de Daimiel National Park wetland (central Spain). We used data from two constant effort mist-netting stations (2005-2013), and spatially explicit capture-recapture Jolly-Seber models. The Reedwarblers continued reproducing in a dry environment for three years after the start of a dry phase, despite progressive declines in productivity, and ultimately stopped nesting in the fourth year. After the recovery of water levels in subsequent years, the population required another four years to recover a size and productivity similar to those preceding the drought. This situation may be common in the near future given ongoing alterations of the hydroperiod in
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