Animals may perceive humans as a form of predatory threat, a disturbance, triggering behavioral changes together with the activation of physiological stress responses. These adaptive responses may allow individuals to cope with stressful stimuli, but a repeated or long-term exposure to disturbances may have detrimental individual-and population-level effects. We studied the effects of human activities, particularly hunting, on the behavior and physiological status of a near-threatened nongame steppe bird, the little bustard. Using a semiexperimental approach, we compared before, during, and after weekends: 1) the type and intensity of human activities and 2) the behavior and 3) physiological stress (fecal corticosterone metabolites) of wintering birds. Higher rates of human activity, in particular those related to hunting, occurred during weekends and caused indirect disturbance effects on birds. Little bustards spent more time vigilant and flying during weekends, and more time foraging in the mornings after weekend, possibly to compensate for increased energy expenditure during weekends. We also found increased physiological stress levels during weekends, as shown by higher fecal glucocorticoid metabolite concentrations. Increased corticosterone metabolite levels were associated with the highest levels of hunting-related disturbances. Little bustard showed marked behavioral and physiological (stress hormones) responses to human activities that peaked during weekends, in particular hunting. The long-term effect of this particular activity carried out during weekends from autumn throughout winter might adversely impact wintering populations of this nongame endangered species, potentially counteracting conservation efforts conducted on local as well as foreign breeding populations.
Farmland bird populations have declined sharply due to agricultural intensification. In Europe, these negative population trends have been linked to the loss of semi‐natural vegetation types, particularly fallow land. The work of Sanz‐Pérez et al. (2019) has far‐reaching implications for the conservation of farmland biodiversity. We argue that it supports a new paradigm for the understanding and management of fallows that should be integrated into the forthcoming post‐2020 Common Agricultural Policy (CAP). Following the abolition of mandatory set‐aside by the European Union in 2008, fallows declined steadily in Europe until 2015, when the CAP implemented greening measures. These restored the requirement to leave 5% of arable land as ecological focus areas (EFAs) to enhance biodiversity. While fallows are one of the most beneficial forms of EFA for farmland birds, farmers prefer the less conservation effective planting of nitrogen‐fixing and catch crops (currently more than 70% of EFAs). CAP incentives have been insufficient to make unproductive EFAs such as fallows more attractive to farmers. Sanz‐Pérez et al. (2019) evaluated the impact of different fallow land management practices on the abundance of specialist farmland birds. They concluded that extensive practices – such as tilling or shredding once or twice per year before the breeding season – were more beneficial to these declining species than leaving fallows unmanaged and recommended their incorporation into agri‐environment schemes. But such schemes have had low uptake, and thus a limited potential to drive the widespread recovery of farmland birds at either national or European levels. The post‐2020 CAP, currently under development, should integrate simple fallow management practices within new conditionalities or eco‐schemes to address this problem. Synthesis and applications. The loss of fallow land underlies the decline of farmland birds. The post‐2020 CAP must overcome past mismatches between incentives to farmers and biodiversity benefits and increase farmers’ uptake of the most beneficial options for biodiversity, including fallows. Promoting light management of fallow land within the new CAP eco‐schemes is a win–win strategy because it would simultaneously allow farmers to continue extensive weed control and enhance habitat quality for farmland birds.
In order for competing species to coexist, segregation on some ecological niche component is required and is often mediated by differential habitat use. When unequal competitors are involved, the dominant species tends to displace the subordinate one to its less preferred habitat. Here, we use habitat isodars, an approach which reflects evolutionary stable strategies of habitat selection, to evaluate whether interspecific competition between two competing species with distinct habitat preferences, the little bustard Tetrax tetrax and the great bustard Otis tarda, modulates their habitat use. Field data on these endangered species demonstrate that unequal competitors can coexist without completely segregating on their preferred habitats. The negatively sloped isodar of the subordinate little bustard unveils its competition with the dominant great bustard.Interference from great bustards in secondary cereal habitats reinforces use of preferred natural habitat by little bustards. Studies of density-dependent habitat selection by a single-species can thus aid in identifying the effects of competition on community composition, and guide the conservation of at-risk species. Isodars, in particular, represent a promising method to gain clear knowledge on interspecific competition for species in which experimental manipulations are not feasible.
Interspecific competition is a dominant force in animal communities that induces niche shifts in ecological and evolutionary time. If competition occurs, niche expansion can be expected when the competitor disappears because resources previously inaccessible due to competitive constraints can then be exploited (i.e., ecological release). Here, we aimed to determine the potential effects of interspecific competition between the little bustard (Tetrax tetrax) and the great bustard (Otis tarda) using a multidimensional niche approach with habitat distribution data. We explored whether the degree of niche overlap between the species was a density‐dependent function of interspecific competition. We then looked for evidences of ecological release by comparing measures of niche breadth and position of the little bustard between allopatric and sympatric situations. Furthermore, we evaluated whether niche shifts could depend not only on the presence of great bustard but also on the density of little and great bustards. The habitat niches of these bustard species partially overlapped when co‐occurring, but we found no relationship between degree of overlap and great bustard density. In the presence of the competitor, little bustard's niche was displaced toward increased use of the species' primary habitat. Little bustard's niche breadth decreased proportionally with great bustard density in sympatric sites, in consistence with theory. Overall, our results suggest that density‐dependent variation in little bustard's niche is the outcome of interspecific competition with the great bustard. The use of computational tools like kernel density estimators to obtain multidimensional niches should bring novel insights on how species' ecological niches behave under the effects of interspecific competition in ecological communities.
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