BackgroundReports from UK hunters of ‘rice grains’ in muscles of shot wildfowl (Anatidae) coincided temporally with the finding of sarcocystosis in a number of ducks found as part of the Wildfowl & Wetlands Trust long-term general surveillance of found dead waterbirds. Sarcocystis rileyi has also been relatively recently confirmed in wildfowl in north-eastern Europe.MethodsThis study uses four approaches to investigate UK wildfowl sarcocystosis: first, through a hunter questionnaire that captured historical case data; secondly, through an online reporting system; thirdly, DNA sequencing to characterise UK cases; and fourthly, histological myopathy assessment of infected pectoral muscle.ResultsOur questionnaire results suggest Sarcocystis infection is widely distributed throughout the UK and observed in 10 Anatidae species, reported cases increased since the 2010/2011 shooting season, with the online reporting system reflecting this increase. DNA sequencing (18S rRNA gene and internal transcribed spacer-1 region) of UK isolates confirmed S rileyi in the five dabbling duck host species tested and the associated histopathological myopathy is described.ConclusionThis work highlights an emerging issue to European wildfowl species and provides much opportunity for further research, including the impacts of S rileyi and the described myopathy on host health, fitness and survival.
Globally, there is increasing effort to transition away from the use of lead ammunition to mitigate its known risks to wildlife and human health. Whenever this transition is stated hunters frequently cite concerns about the effectiveness of non‐lead ammunition, how it will result in greater crippling rates, and associated animal welfare costs. This area has been little studied, but recent studies have found no differences in crippling rates using lead and steel ammunition. Using segmented linear regression we evaluated 37 years of waterfowl harvest data in Illinois, United States, overlapping the transition to non‐lead shot for waterfowl hunting in order to assess how crippling rates changed following the ban. The average crippling rate prior to the lead shot ban was 23% for both ducks and geese and reduced to an average of 15% and 11% for ducks and geese (respectively) following the ban. In addition, the annual trend in the proportion of ducks and geese crippled reversed following the ban, from a significant annually increasing to a significant annually decreasing trend. We offer hypotheses on behavioural and technological changes which may explain these changes and predict that crippling losses will not increase in Europe following a ban on the use of lead ammunition over wetlands in 2023.
1. There is a need to assess the sustainability of wild bird harvest in the United Kingdom (UK), and more widely, across Europe. Yet, data on populations and harvest sizes are limited.2. We used a demographic invariant method (DIM) to estimate potential excess growth (PEG) for populations of UK wintering waterbirds and calculated a sustainable harvest index (SHI) for each. We compared this with population trends and conservation classifications (e.g. Birds of Conservation Concern [BoCC]) to assess the sustainability of harvests and the utility of these classifications.3. Our approach found evidence for potential overharvest of mallard Anas platyrhynchos, Eurasian teal Anas crecca, gadwall Mareca strepera, Canada geese Branta canadensis, greylag geese Anser anser and woodcock Scolopax rusticola.Whether DIM methods predict overharvest is highly dependent on estimates of maximum population growth rates inferring PEG. We found estimates of maximum population growth to be variable across a range of different methods.4. We found no relationship between SHI and short-term wintering trends or conservation classification under the UK's BoCC framework. There was however a positive relationship between SHI and long-term wintering trends. 5. Policy implications. Our results suggest that UK-based harvest is unlikely to be a major determinant of population trends for the majority of UK overwintering waterbirds, but harvest rates for some species may exceed that required to maintain stationary population growth. The lack of a relationship between conservation classifications and SHI strongly suggests that such conservation classifications are not an appropriate tool for making decisions about harvest management. Instead, our assessment provides the basis for a framework to make evidence-based decisions on sustainable harvest levels in the face of incomplete data. There is currently no clear policy instrument in the UK to support such a framework via controls on either harvest effort or mortality of waterfowl.We believe such an instrument is urgently needed to ensure the UK can adapt to changing pressures and ensure the sustainable use of our wildlife populations.
Crippling loss (waterfowl downed, but not retrieved) is a recognized component of waterfowl harvest, but there are few contemporary estimates. We used a zero-inflated negative binomial model to account for false reporting of zeros and estimated waterfowl crippling losses from harvest data reported in a 2018-2019 survey of waterfowl hunters in Illinois, USA. We found that crippling rates declined rapidly with increasing harvest and moderately with increasing days afield. For the most active hunters (days afield), the probability of falsely reporting zero crippling loss increased with the number of ducks they reported harvesting, whereas for the least active hunters we found the reverse. We suggest that modest improvements in hunter skill could produce significant reductions in crippling loss.
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