Number of common ravens observed at the studied landfill (waste storage centre of Saint-Flour, central France) during the different resighting protocols (see methods) before, during and after non-lethal shots performed in the roosts and surrounding foraging areas during the evenings of the 23 and 24 July 2016

Number of common ravens observed at the studied landfill (waste storage centre of Saint-Flour, central France) during the different resighting protocols (see methods) before, during and after non-lethal shots performed in the roosts and surrounding foraging areas during the evenings of the 23 and 24 July 2016

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Some protected species have benefited from human activities to a point where they sometimes raise concerns. However, gaps in knowledge about their human-related behaviour hamper effective management decisions. We studied non-breeding common ravens Corvus corax that aggregated and predated livestock in the surroundings of a landfill. Combining sever...

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... In crows, several studies concluded that culling is ineffective in reducing the numbers (Jiguet, 2020;Preininger et al., 2019) because of their specific group dynamics. Immature crows gather in large groups at sites where food is abundant and move regularly between groups, function as metapopulations at broad spatial scales (Marchand et al., 2018). ...
... In crows, several studies concluded that culling is ineffective in reducing the numbers (Jiguet, 2020;Preininger et al., 2019) because of their specific group dynamics. Immature crows gather in large groups at sites where food is abundant and move regularly between groups, function as metapopulations at broad spatial scales (Marchand et al., 2018). Culling at local scale is therefore not effective in reducing numbers at large spatial scale so that hunting needs to be organized on a large scale to be effective, which, in turn is logistically and ethically ...
... One-time disturbances or relocations do not reduce raven numbers over the long term, and even successful curtailment of further raven growth may simply plateau abundances at undesirable levels (Coates et al. 2007, Marchand et al. 2018. In the absence of continued management, long-lived breeders can simply return to the territory the following year to renest, or re-placement breeders may instead move into the prematurely vacated nesting territories (Boarman 2003, Webb et al. 2004). ...
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Some avian species have developed the capacity to leverage resource subsidies associated with human manipulated landscapes to increase population densities in habitats with naturally low carrying capacities. Elevated corvid densities and new territory establishment have led to an unsustainable increase in depredation pressure on sympatric native wildlife prey populations as well as in crop damage. Yet, subsidized predator removal programs aimed at reducing densities are likely most effective longer-term when conducted in tandem with subsidy control, habitat management, and robust assessment monitoring programs. We developed decision support software that leverages stage structured Lefkovitch population matrices to compare and identify treatment strategies that reduce subsidized avian predator densities most efficiently, in terms of limiting both cost and take levels. The StallPOPd (Version 4; available at https://doi.org/10.7298/sk2e-0c38.4) software enables managers to enter the area of their management stratum and the demographic properties (vital rates) of target bird population(s) of interest to evaluate strategies to decrease or curtail further population growth. Strategies explicitly include the reduction in fertility (i.e., eggs hatched) and/or the culling of hatchlings, non-breeders and/or breeders, but implicitly comprise reduction in survival or reproduction through subsidy denial. We illustrate the utilities of the software with examples using common ravens (Corvus corax; ravens) in the Mojave Desert of California, USA. Unfortunately, the survival and reproduction effects of each unit of a particular subsidy in that system have remained elusive, though this is the priority of current research. Because the software leverages a life history representation that is known to characterize hundreds of wildlife species in addition to ravens, the work expands the suite of tools available to wildlife managers and agricultural industry specialists to abate bird damage and impacts on sensitive wildlife in habitats with persistent human subsidies.
... With the capacity for widespread movements, non-breeders raise concerns regarding spill-over predation, whereby individuals subsidized by AFSs invade adjacent areas, inflating predation and impacting trophic networks there [37,38]. Far-ranging flights also pose a challenge for the nonlethal conservation management of problematic nonbreeder populations, such as translocations [39] and the control of food sources [25]. Addressing these issues are complex as within non-breeder groups, individuals can differ widely in terms of foraging preferences and space use [33,40,41], based on age and origin (e.g., wild-reared versus released from captivity) cohorts [33,42] and on external factors (e.g., resource type, seasonality of the environment) [23,31]. ...
... The averaged maximum daily displacement (presented on a logarithmic scale) also differed between d adults and juveniles, e captive-released and wild-caught individuals, but not f seasonally. White circles with red error bars depict model-averaged estimates from a generalised linear mixed model (GLMM), with 95% confidence intervals (Table 2) from problem areas, targeting less vagrant juveniles, who are also easier to capture [39], may prove to be more effective than wide-ranging adults. ...
... In temperate climates, natural food source availability decreases starting autumn through winter, and increases once again in spring. Avian scavengers, like ravens, can experience higher food-searching costs in low temperatures, high snow cover (which hides natural food sources), short day lengths, and limited opportunities for good flight conditions (e.g., fewer thermal uplifts in winter reduces flight distance and duration) [23,31,39,49,79]. When conditions get warmer, anthropogenic food availability in temperate regions can change as large amounts of garbage melt out of the snow [32], and as organic waste is raked out of barns to compost in the warming weather. ...
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Background Anthropogenic food sources (AFSs) are widespread in human-transformed landscapes and the current scale at which they occur drives ecological change at the individual, population, and community levels. AFSs are exploited extensively by common ravens, Corvus corax . Understanding how raven populations use AFSs can provide insight into their ecological responses to AFSs. Methods We equipped 81 ravens in the Austrian Alps with GPS-transmitters over a period of 2.75 years. Using these tracking data, we investigated how cohort differences (i.e., age, sex, and origin) and seasonal changes influence raven movement patterns (i.e., occurrence distribution and maximum daily displacement) and AFS-use (i.e., number of AFSs visited and probability of being present at any AFS) at 45 extensively exploited sites. Results We found that proxies for experience and dominance, inferred by age (i.e., juvenile versus adult) and origin (i.e., wild-caught versus captive-bred-released) cohorts, influenced movement patterns and the number of AFSs visited. However, all individuals were equally likely to be present at AFSs, highlighting the importance of AFSs for non-breeders in the study population. Seasonal changes in environmental conditions that affect energetic demands, the availability of natural and anthropogenic food, and foraging competition, influenced individuals’ occurrence distributions and AFS-use. We found that under harsher conditions in autumn and winter, individuals ranged wider and depended on AFSs to a larger degree. However, contrary to expectation, they were less likely to be present at AFSs in these seasons compared to spring and summer, suggesting a trade-off between time spent moving and exploiting resources. We attribute the small ranging movements exhibited by non-breeders in spring and summer to the presence of highly territorial and socially dominant breeders. As breeders mostly stay and forage within their territories during these seasons, competition at AFSs decrease, thereby increasing the likelihood of individuals being present at any AFS. Conclusions We emphasize that movement and AFS-use differ according to cohort differences and the seasonality of the environment. Our results highlight that predictable AFSs affect foraging strategies among non-breeding ravens. The extent of AFS-exploitation among non-breeding ravens in our study emphasize the potential of AFSs in shaping raven movement and resource-use.
... As a consequence, culling is largely implemented to regulate corvid numbers, and long-term repeated trapping during the breeding season can durably reduce their densities (Díaz-Ruiz et al. 2010;Chiron and Julliard 2013;Kövér et al. 2018a). However, in most study cases, culling is inefficient to reduce numbers (Preininger et al. 2019) and so damages, because of the local scale of trapping and the large spatial scale of metapopulation dynamics (Marchand et al. 2018;Lorreto et al. 2017). Indeed, large-scale long-term culling cannot be implemented efficiently when the nuisance is only local. ...
... Despite initial dispersal upon laser treatment, American crows Corvus brachyrhynchos returned to treated urban roosts within 15 min (Gorenzel et al. 2002). Similarly, scaring with distress calls marginally reduced Corvus corax numbers at roost but during a single night only (Marchand et al. 2018). Finally, translocations are expensive and do not prevent displaced individuals to return, because nonbreeding individuals are highly mobile within very large home ranges (Marchand et al. 2018). ...
... Similarly, scaring with distress calls marginally reduced Corvus corax numbers at roost but during a single night only (Marchand et al. 2018). Finally, translocations are expensive and do not prevent displaced individuals to return, because nonbreeding individuals are highly mobile within very large home ranges (Marchand et al. 2018). As most current control strategies seem inefficient (Jiguet 2020), it appears necessary to look for other solutions to reduce or mitigate the damages. ...
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Urban crows feed mainly on food wastes, also often dig up plantations and uproot grass in search of soil invertebrates, locally leading to extended damages to flower and lawn beds. Lethal methods to reduce crow numbers are largely inefficient, because of the large spatial scale of metapopulation dynamics. We tested experimentally if the mowing management of lawns could reduce grass uprooting by foraging crows in Paris during two consecutive years. Six lawn beds were mown as usual, six others remained unmown from September until February when we estimated the uprooted extend and the abundance of underground invertebrates. Unmowing led to taller grass, higher invertebrate abundances and a reduction of uprooting by 50%. It is ethically more acceptable than any lethal method, and provides economic benefits, by reducing the costs of lawn restoration, but also of mowing. We conclude that restricted mowing is ecologically, economically and ethically efficient to reduce grass uprooting by foraging urban crows. Graphical abstract
... However, recent investigations in corvid dispersal and dynamics provide elements challenging the efficiency of any local control intended to reduce numbers (Heinemann et al., 2020). Immense individual home ranges and fusion-fission group dynamics (Loretto et al., 2017) have been documented in ravens Corvus corax and crows (Uhl, 2016) rendering any local initiative to reduce numbers inefficient (Marchand et al., 2018). Immature ravens and crows gather in large groups at sites where food is abundant and predictable, while birds move regularly and individually between such groups, functioning in metapopulations at broad spatial scales, up to 40,000 km2 in a French raven population (Marchand et al., 2018;see Fig. 2). ...
... Immense individual home ranges and fusion-fission group dynamics (Loretto et al., 2017) have been documented in ravens Corvus corax and crows (Uhl, 2016) rendering any local initiative to reduce numbers inefficient (Marchand et al., 2018). Immature ravens and crows gather in large groups at sites where food is abundant and predictable, while birds move regularly and individually between such groups, functioning in metapopulations at broad spatial scales, up to 40,000 km2 in a French raven population (Marchand et al., 2018;see Fig. 2). Any local damages can not be solutioned by culling locally, as the local turnover of individuals is high (0.68 in Marchand et al., 2018), and the metapopulation is far larger than the local population. ...
... Immature ravens and crows gather in large groups at sites where food is abundant and predictable, while birds move regularly and individually between such groups, functioning in metapopulations at broad spatial scales, up to 40,000 km2 in a French raven population (Marchand et al., 2018;see Fig. 2). Any local damages can not be solutioned by culling locally, as the local turnover of individuals is high (0.68 in Marchand et al., 2018), and the metapopulation is far larger than the local population. As a consequence, any efficient control could only occur at those spatial scales able to alter the spatial dynamics of the species. ...
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The recent discovery that cats and mustelids can be infected by SARS-CoV-2 may raise the question of monitoring domestic, feral and wild populations of such animals, as an adjunct to the elimination of COVID-19 in humans. Emergency solutions might consider large scale control of these animals in the wild. However, looking at science recently published on native vertebrate pest control reveals first that usual controls do not succeed in reducing animal numbers and associated damages, second that controlling can be counter-productive in increasing the infectious risks for humans and livestock. The examples of red fox and corvids are detailed in a European context, illustrating the urgent need for an ethical evaluation of ecological and economic costs and benefits of pest control strategies. A complete scientific evaluation process must be implemented and up-dated regularly, to be organized in four major steps, once the aim of the control strategy has been defined: (1) evaluating damages/risks caused by the animals, to be balanced with the ecosystem services they may provide, also in terms of economic costs; (2) unravelling spatial and temporal population dynamics of target animals to identify, if any, optimal control scenarios – which could be done within an adaptive management framework; (3) estimating the economic costs of implementing those optimal control scenarios, to be compared to the economic costs of damages/diseases; (4) finally evaluating how the control strategy reached its aims. A modern fable of the Fox and the Crow should deliver a timely moral for an ethical, ecological and economical appraisal of pest control strategies in Europe.
... The likely dispersal distances identified by Heintze a century ago are remarkably similar to known movement distances in present-day corvids in northern Europe (see also Cramp and Perrins, 1994;e.g., Wernham et al., 2002;Fransson and Hall-Karlsson, 2008;Czarnecka and Kitowski, 2010;Pesendorfer et al., 2016;Marchand et al., 2018). This confirms that corvids are important vectors for long-distance dispersal of plants, and offer a maximum dispersal distance far greater than is generally recorded for other mechanisms including epizoochory, anemochory, and obviously barochory (Bullock et al., 2017). ...
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It is well-known that some members of the crow family (Corvidae) are important for seed dispersal either via frugivory (e.g., when feeding on berries) or by scatter hoarding (e.g., of nuts). Dispersal via gut passage of seeds within a fleshy fruit can be considered “classical endozoochory.” However, corvids are rarely recognized as vectors of plants lacking a fleshy fruit, or a large nut (such as plants with a dry achene, capsule or caryopsis). Dispersal of such seeds via gut passage can be considered “non-classical endozoochory.” A century ago, Heintze (1917a,b); Heintze (1918) reported on extensive field studies of seed dispersal by 11 species of European Corvidae. His work is overlooked in contemporary reviews of corvid biology. We resurrect his work, which suggests that contemporary views about seed dispersal by corvids are too narrow. Heintze identified 157 plant taxa from 42 families which were dispersed by corvids by endozoochory, as well as another nine taxa only dispersed by synzoochory (which includes scatter-hoarding). Most (54%) of the plant species dispersed by endozoochory lack a fleshy fruit and have previously been assigned to other dispersal syndromes, mainly associated with wind (10%), self-dispersal (22%) or epizoochory (18%). Plants lacking a fleshy fruit were particularly well-represented from the Caryophyllaceae (12 species), Poaceae (14 species), and Polygonaceae (8 species). Of 27 taxa germinated by Heintze from seeds extracted from corvid pellets or feces (71% of those tested), 20 lack a fleshy fruit. Similarly, of 32 taxa he recorded as seedlings having germinated from pellets in the field, 11 lacked a fleshy fruit. However, Heintze's quantitative data show that classical endozoochory is dominant in Magpies Pica pica and Hooded Crows Corvus cornix, for which 97% of seeds dispersed were fleshy-fruited. Corvids overlap with waterfowl as vectors of terrestrial plants dispersed by non-classical endozoochory, and 56 species are dispersed by both corvids and dabbling ducks according to the lists of Heintze and Soons et al. (2016). Finally, Heintze's data show that corvids were already dispersing alien plants in Europe a century ago, such as the North American Dwarf Serviceberry Amelanchier spicata.