Summary1. Ravens ( Corvus corax , L.) feed on rich but ephemeral carcasses of large animals. Nonbreeding juveniles forage socially and aggregate in communal winter roosts, which may function as 'information centres' regarding food locations. 2. In a large roost in North Wales, regurgitated pellets on the forest floor contained a variety of prey remains, which were more similar for ravens that had roosted close together the same night. 3. Sheep carcasses placed at varying distances from the roost were baited with colourcoded plastic beads. These were ingested and regurgitated in pellets back at the roost in aggregations, the spatial distribution of which consistently reflected the geographical location of bait sites. 4 Aggregations of beads at the roost grew daily with an increasing radius centred upon the first pellet per carcass. This mirrored the linear increase of six birds per day in the size of groups flying between roost and carcass each morning. Rates of recruitment were greater for carcasses closer to the roost. 5 Groups were led by a single bird roosting centrally within the aggregation. When individually identifiable (37·5% of cases), these individuals were dominant at the carcass and were among the minority of birds involved in acrobatic display flights at preroost gatherings. 6 When contrasted with data on two alternative groups of ravens peripheral to the main roost which foraged and roosted collectively, these results provide strong circumstantial evidence for raven roosts as structured information centres. The adaptive basis for competitive recruitment resulting in excessively large group sizes is also discussed.

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Leukocyte telomeres shorten with age, and excessive shortening is associated with age-related cardiometabolic diseases. Exercise training may prevent disease through telomere length maintenance although the optimal amount of exercise that attenuates telomere attrition is unknown. Furthermore, the underlying molecular mechanisms responsible for the enhanced telomere maintenance observed in endurance athletes is poorly understood. We quantified the leukocyte telomere length and analyzed the expression of telomere-regulating genes in endurance athletes and healthy controls (both n = 61), using quantitative PCR. We found endurance athletes have significantly longer (7.1%, 208-416 nt) leukocyte telomeres and upregulated TERT (2.0-fold) and TPP1 (1.3-fold) mRNA expression compared with controls in age-adjusted analysis. The telomere length and telomere-regulating gene expression differences were no longer statistically significant after adjustment for resting heart rate and relative V̇O(2 max) (all P > 0.05). Resting heart rate emerged as an independent predictor of leukocyte telomere length and TERT and TPP1 mRNA expression in stepwise regression models. To gauge whether volume of exercise was associated with leukocyte telomere length, we divided subjects into running and cycling tertiles (distance covered per week) and found individuals in the middle and highest tertiles had longer telomeres than individuals in the lowest tertile. These data emphasize the importance of cardiorespiratory fitness and exercise training in the prevention of biological aging. They also support the concept that moderate amounts of exercise training protects against biological aging, while higher amounts may not elicit additional benefits.

Natural experiments have been proposed as a way of complementing manipulative experiments to improve ecological understanding and guide management. There is a pressing need for evidence from such studies to inform a shift to landscape‐scale conservation, including the design of ecological networks. Although this shift has been widely embraced by conservation communities worldwide, the empirical evidence is limited and equivocal, and may be limiting effective conservation. We present principles for well‐designed natural experiments to inform landscape‐scale conservation and outline how they are being applied in the WrEN project, which is studying the effects of 160 years of woodland creation on biodiversity in UK landscapes. We describe the study areas and outline the systematic process used to select suitable historical woodland creation sites based on key site‐ and landscape‐scale variables – including size, age, and proximity to other woodland. We present the results of an analysis to explore variation in these variables across sites to test their suitability as a basis for a natural experiment. Our results confirm that this landscape satisfies the principles we have identified and provides an ideal study system for a long‐term, large‐scale natural experiment to explore how woodland biodiversity is affected by different site and landscape attributes. The WrEN sites are now being surveyed for a wide selection of species that are likely to respond differently to site‐ and landscape‐scale attributes and at different spatial and temporal scales. The results from WrEN will help develop detailed recommendations to guide landscape‐scale conservation, including the design of ecological networks. We also believe that the approach presented demonstrates the wider utility of well‐designed natural experiments to improve our understanding of ecological systems and inform policy and practice.