5 research outputs found

    Understanding Animal Group-Size Distributions

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    One of the most striking aspects of animal groups is their remarkable variation in size, both within and between species. While a number of mechanistic models have been proposed to explain this variation, there are few comprehensive datasets against which these models have been tested. In particular, we only vaguely understand how environmental factors and behavioral activities affect group-size distributions. Here we use observations of House sparrows (Passer domesticus) to investigate the factors determining group-size distribution. Over a wide range of conditions, we observed that animal group sizes followed a single parameter distribution known as the logarithmic distribution. This single parameter is the mean group size experienced by a randomly chosen individual (including the individual itself). For sparrows, the experienced mean group size, and hence the distribution, was affected by four factors: morning temperature, place, behavior and the degree of food spillage. Our results further indicate that the sparrows regulate the mean group size they experience, either by groups splitting more or merging less when local densities are high. We suggest that the mean experienced group size provides a simple but general tool for assessing the ecology and evolution of grouping

    Experience buffers extrinsic mortality in a group-living bird species

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    Extrinsic mortality has a strong impact on the evolution of life-histories, prey morphology and behavioural adaptations, but for many animals the causes of mortality are poorly understood. Predation is an important driver of extrinsic mortality and mobile animals form groups in response to increased predation risk. Furthermore, in many species juveniles suffer higher mortality than older individuals, which may reflect a lower phenotypic quality, lower competitiveness, or a lack of antipredator or foraging skills. Here we assessed the causes of mortality for 371 radio tagged Siberian jays. This sedentary bird species lives in family groups that contain a breeding pair as well as related and unrelated non-breeders. Ninety-five percent of death were due to predation (n = 59 out of 62 individuals) and most individuals were killed by Accipiter hawks. Multivariate Cox proportional hazards models showed that non-breeders had a lower survival than breeders, but only in territories in managed forest with little visual cover. Examining breeders, only sex influenced survival with males having a lower survival than females. For non-breeders, juveniles had lower survival than older non-breeders, and those on managed territories had lower survival than those on unmanaged territories. Additionally, a low feather quality reduced the survival probability of non-breeders only. Thus, living on managed territories and having a low feature quality affected only non-breeders, particularly juveniles. These findings add to previous research demonstrating that juvenile Siberian jays acquire critical antipredator skills from experienced group members. Thus, experience can buffer extrinsic mortality, highlighting that group living not only provides safety in numbers, but also provide social opportunities to learn critical life-skills

    Linking climate change vulnerability research and evidence on conservation action effectiveness to safeguard European seabird populations

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    Publisher Copyright: © 2022 British Ecological Society.An increasing number of species are facing unprecedented levels of threat to their long-term survival due to the direct and indirect impacts of climate change. Key opportunities for science to inform wildlife management are linked to increasing our understanding of how changes in climatic conditions will impact species, as well as whether, and how, managers may facilitate species' ability to adapt to change. However, information on species' climate change vulnerability and the effectiveness of potential conservation actions are not yet strategically collected or collated; this disconnect between threat level, ecological research and conservation practice is reducing the opportunities to guide decision-making, ultimately hindering conservation outcomes. To demonstrate this point, we explore how existing knowledge can be brought together in a pressure-state-response framework that connects climate change ecology, conservation evidence assessments and management. Seabirds in Western Europe are used as a case study, as they are well-researched and vulnerable to climate change. Using a combination of literature reviews and surveys, we identify the main threats posed to seabirds in the region by climate change, as well as existing conservation actions that could be applied to lessen the impacts of each of these threats. Our results show that 29% of the types of actions considered for reducing the impacts of climate change on seabirds are either associated with conflicting evidence or lack sufficient information to make robust conclusions about their effectiveness: actions aiming at restoring or creating habitat, encouraging relocation, treating or preventing disease, and reducing inter-species competition all have limited or mixed evidence to support their use. Moreover, several threats identified by conservation practitioners as being of high priority to address, such as changes in prey abundance and eutrophication, have few or no viable identified actions to reduce their impact on seabirds. Synthesis and applications. We suggest that existing knowledge on species vulnerability to climate change and evidence of conservation action effectiveness should be more commonly brought together in tailored pressure-state-response frameworks. Such an approach provides an easily transferable platform for identifying missing information and areas where connections between research and management need to be tightened to improve conservation outcomes.Peer reviewe
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