Corvids are often viewed as efficient predators capable of limiting prey species populations. Despite this widely held belief, a comprehensive review quantifying the effect of corvids on the ...demography of prey species is lacking. We examine the impacts of crows, ravens Corvus spp. and Eurasian Magpies Pica pica on the population parameters of other bird species. We summarize results from 42 studies, which included 326 explicit evaluations of relationships between a corvid and a potential prey species. Population parameters of studied prey species were categorized as abundance‐related (numbers, nest density) or productivity‐related (nest success, brood size). Information from both experimental removal studies and correlative studies was examined. Combining all studies, no negative influence of corvids on either abundance or productivity of prey species was found in 81% of cases. Negative impacts were significantly more likely in cases examining productivity rather than abundance (46 vs. 10%). Experimental studies that removed only corvid species were significantly less likely to show a positive impact on productivity than those removing corvids alongside other predators (16 vs. 60%). This suggests that the impact of corvids is smaller than that of other predators, or that compensatory predation occurs. The impact of corvids was similar between diverse avian groups (such as gamebirds, passerines and waders; or ground‐nesting and other species). Crows were found to be significantly more likely to have a negative impact on prey species productivity than were Magpies (62 vs. 12%), but no differences were found in relation to prey abundance. We conclude that while corvids can have a negative impact on bird species, their impact is small overall, and nearly five times more frequent for productivity than for abundance. These results suggest that in most cases bird populations are unlikely to be limited by corvid predation and that conservation measures may generally be better targeted at other limiting factors. However, negative impacts were found in a minority of cases, and those may require further investigation to develop management tools to mitigate such impacts where they are of economic or conservation concern.
Resurgence refers to the relapse of a target behavior following the worsening of a source of alternative reinforcement that was made available during response elimination. Most laboratory analyses of ...resurgence have used a combination of extinction and alternative reinforcement to reduce target behavior. In contingency‐management treatments for alcohol use disorder, however, alcohol use is not placed on extinction. Instead, participants voluntarily abstain from alcohol use to access nondrug alternative reinforcers. Inasmuch, additional laboratory research on resurgence following voluntary abstinence is warranted. The present experiment evaluated resurgence of rats' ethanol seeking following voluntary abstinence produced by differential reinforcement of other behavior (DRO). Lever pressing produced ethanol reinforcers during baseline phases. During DRO phases, lever pressing continued to produce ethanol and food reinforcers were delivered according to resetting DRO schedules. Ethanol and food reinforcers were suspended during resurgence test phases to evaluate resurgence following voluntary abstinence. Lever pressing was elevated during baseline phases and occurred at near‐zero rates during DRO phases. During the resurgence test phases, lever pressing increased, despite that it no longer produced ethanol. The procedure introduced here may help researchers better understand the variables that affect voluntary abstinence from ethanol seeking and resurgence following voluntary abstinence.
Abstract In treatments based on differential reinforcement of alternative behavior, applied researchers and clinicians often provide multiple, qualitatively different reinforcers (i.e., synthesized ...reinforcement) rather than a single reinforcer (i.e., isolated reinforcement) contingent on alternative behavior. Some research shows that providing synthesized reinforcement for alternative responses within such treatments produces more rapid and complete suppression of target behavior; however, there is limited research evaluating the durability of these effects during treatment disruptions. Conceptual explanations of resurgence (e.g., resurgence as choice, context theory) suggest that treatments that include synthesized alternative reinforcement may lead to more resurgence of target behavior when alternative reinforcement is disrupted relative to treatments using isolated reinforcement. We evaluated this hypothesis within a three‐phase resurgence evaluation. We exposed rats to isolated or synthesized reinforcement for alternative responding in the second phase, and we exposed rats to extinction in the third phase. Synthesized alternative reinforcement produced more rapid and complete suppression of target behavior than did isolated reinforcement in the second phase; however, exposure to extinction following synthesized reinforcement produced more resurgence. We discuss these results in terms of their implications for applied research and their support for current conceptual explanations for resurgence.
Conventional approaches for the assessment of population abundance or trends are usually based on a single source of information, such as counts or changes in demographic parameters. However, these ...approaches usually neglect some of the information needed to properly understand the population as a whole, such as assessments of the non-breeding proportion of the population and the drivers of population change. The Bearded Vulture Gypaetus barbatus is a threatened species and its Pyrenean population (the largest in Europe) inhabits parts of Spain, Andorra, and France. We developed an Integrated Population Model (IPM) using data from a long-term study (1987–2016) in the three countries, including capture–mark–recapture of 150 marked individuals, to assess population size and age structure at the whole population scale, and obtain estimates of survival and breeding parameters of this population. The breeding population experienced a geometric mean population increase of 3.3% annually, falling to 2.3% during the last 10 yr. The adult proportion of the population increased with time, from 61% to 73%. There were 365 (95% Bayesian credible interval BCI: 354–373) adult breeding birds in 2016, representing 49% of the adult population and 36% of the total population (estimated at 1,026 individuals, 95% BCI: 937–1,119). The large number of non-breeding adults probably led to higher mean age of first reproduction than previously estimated, and to an estimated 30–35% of territories occupied by polyandrous trios. Population growth rate was positively and strongly correlated with adult survival, which had a much greater effect on population growth than productivity. The effects of subadult and juvenile survival on population growth were weaker. We found strong evidence for a density-dependent decrease in juvenile survival, productivity and adult survival, leading to reduced population growth with increased population size. Our approach allowed us to identify important conservation issues related to the management of supplementary feeding sites and geographic expansion of this population. Our study supports the use of IPMs as a tool to understand long-lived species, allowing simultaneous estimates of the non-breeding size of the population (which is critical for understanding population functioning), better estimates of population parameters, and assessment of demographic drivers.
Knowledge of feeding ecology of declining species, such as farmland birds, is essential to address their conservation requirements, especially when their habitats are suffering important reductions ...of trophic resources. In this study, we apply a metabarcoding approach to describe the diet composition of six of the most significant farmland birds inhabiting European cereal pseudo-steppes: little bustard, great bustard, pin-tailed sandgrouse, black-bellied sandgrouse, red-legged partridge, and common quail. We further studied seasonal diet variations (autumn to spring) in all species but the common quail, whose diet was studied during spring and summer. We show that study species´ diets mostly consisted of plants, although in the case of little bustard and great bustard arthropods are also highly relevant. Among arthropods, we found high proportions of thrips, arachnids, and springtails, which were previously unreported in their diet, and some taxa that could be used as antiparasitic food. Moreover, we report that little bustard's diet is the least rich of that of all studied species, and that diet of all these species is less diverse in winter than in autumn and spring. Diet composition of these declining species supports the importance of natural and semi-natural vegetation and landscape mosaics that can provide a wide variety of arthropods, plants, and seeds all year-round.
We modelled the distribution of two vulnerable steppe birds, Otis tarda and Tetrax tetrax, in the Western Palearctic and projected their suitability up to the year 2080. We performed two types of ...models for each species: one that included environmental and geographic variables (space-included model) and a second one that only included environmental variables (space-excluded model). Our assumption was that ignoring geographic variables in the modelling procedure may result in inaccurate forecasting of species distributions. On the other hand, the inclusion of geographic variables may generate an artificial constraint on future projections. Our results show that space-included models performed better than space-excluded models. While distribution of suitable areas for T. tetrax in the future was approximately the same as at present in the space-included model, the space-excluded model predicted a pronounced geographic change of suitable areas for this species. In the case of O. tarda, the space-included model showed that many areas of current presence shifted to low or medium suitability in the future, whereas a northward expansion of intermediate suitable areas was predicted by the space-excluded one. According to the best models, current distribution of these species can restrict future distribution, probably due to dispersal constraints and site fidelity. Species ranges would be expected to shift gradually over the studied time period and, therefore, we consider it unlikely that most of the current distribution of these species in southern Europe will disappear in less than one hundred years. Therefore, populations currently occupying suitable areas should be a priority for conservation policies. Our results also show that climate-only models may have low explanatory power, and could benefit from adjustments using information on other environmental variables and biological traits; if the latter are not available, including the geographic predictor may improve the reliability of predicted results.
When the rodents reach peak densities (>1,000 voles/ha), up to 33% of them are infected with tularemia. ...as vole numbers increase, so does the bacterium in the environment. Terrestrial vectors such ...as voles and hares evidently transmit this zoonosis, but a human clinical case involving aquatic crayfish handling was also described in the same region in 2001 during an interepizootic period 12, implying that the bacterium is also present in water. ...both aquatic and terrestrial agents of tularemia coexist in nature in Northwest Spain. Fluctuating mammalian populations shape tularemia epidemiology It has long been accepted that fluctuations in the abundance of wild herbivorous mammals (hares, voles) play a key role in tularemia epidemiology in European countries accumulating the largest numbers of clinical cases (i.e., Sweden, Finland, Czech Republic, Hungary, Spain) 6, 8, 14, 16, 18. Extending vole monitoring to include tularemia, particularly during increasing and outbreak population phases, would provide crucial data to parameterize spatial-temporal models of disease risk and help predict when people engaging in nonoptional (e.g., crop harvesting) and optional (e.g., hare hunting, crayfish fishing) risky activities should adopt appropriate risk-minimizing techniques (e.g., farmers using breathing masks during summer harvests in vole outbreaks, hunters and fisherman using gloves during hare butchering or crayfish cleaning; Fig 1).
The effect of stimuli dimension was assessed on the emergence of transitivity relations by the use of a go/no go procedure and the training of identity relations. Four pigeons were trained under this ...conditions, varying the dimension of stimuli for each pair. Two pigeons were trained on Hue–Shape (A–B), Shape–Hue (B–C) and Shape–Shape (B–B) relations so probe trials consisted of Hue–Hue (A–C), called Hue Condition, whereas the remaining pigeons were trained Shape–Hue (A–B), Hue–Shape (B–C) and Hue–Hue (B–B) so probe trials consisted of Shape–Shape (A–C), called Shape Condition. Results were presented as frequency and latencies of responses, on training trials and probe trials, showing more responses and shorter latencies for positive training trials on the four pigeons. On probe trials there was a more differentiated response for pigeons in the Hue Condition whereas for pigeons in the Shape Condition, a lack of transitivity was found. Latencies did not differ between pigeons on probe trials. The current findings are in accordance with studies of conditional discrimination and the use of different dimensions, where hue results in quicker acquisition than shapes.
Tularemia in humans in northwestern Spain is associated with increases in vole populations. Prevalence of infection with Francisella tularensis in common voles increased to 33% during a vole ...population fluctuation. This finding confirms that voles are spillover agents for zoonotic outbreaks. Ecologic interactions associated with tularemia prevention should be considered.
The little bustard (
) is a steppe bird strongly and negatively influenced by agricultural intensification in Europe. Here, we use the little bustard as a model species to examine how favourability ...(relative occurrence likelihood of a species based on environmental characteristics, such as habitat availability) varies regionally with degree of protection in north-western Spain. The Natura2000 network is one of the main biodiversity conservation tools of the European Union, aiming to protect areas hosting species of conservation concern from unfavourable land-use changes. The network covers many landscapes across the continent, including farmland. Additionally, we examine the relationship between trends in land-use favourability and little bustard population trends over a decade in the Nature Reserve of Lagunas de Villafáfila, a protected area also in the Natura2000 network where active and intense management focused on steppe bird conservation is carried out. Favourability was much greater in Villafáfila than in both protected areas with lower degree of protection and in non-protected areas. Land-use favourability increased slightly between 2011 and 2020 both in and out of protected areas, whereas little bustard populations declined sharply in that period, even in Villafáfila. Spatial variations in little bustard abundance within Villafáfila depended on social attraction (increasing with the number of neighbouring males) but not significantly on small-scale variations in land-use favourability. These results suggest that land-use management in Natura2000 areas needs to be more conservation-focused, favouring natural and seminatural habitats and traditional farming practices to improve land-use favourability for little bustards and other steppe birds. Additional factors, such as field-level agricultural management or social interaction variables that may cause an Allee effect, should be incorporated in little bustard favourability models to improve their use in conservation planning.
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