For species with positive density dependence, costs and benefits of increasing density may depend on environmental conditions, but this has seldom been tested. By examining a colonial seabird (common guillemot) over a period of unprecedented poor food availability, we test two contrasting hypotheses suggesting that birds breeding at high density have: (i) greater leeway to increase foraging effort owing to more effective defence of unattended chicks against predators; and (ii) less leeway, owing to more attacks on unattended chicks by neighbouring adults. Supporting hypothesis 1, birds at high density increased provisioning rates and hence survival of chicks by foraging simultaneously with their partners, whereas at low density, unattended chicks were liable to be killed by predatory gulls and, unexpectedly, razorbills. Simultaneously, supporting hypothesis 2, heightened aggression towards unattended chicks at high density frequently resulted in infanticide, undermining benefits from collective defence against predators. Consequently, over 25 years, the magnitude of positive density dependence was independent of mean breeding success. These data indicate previously unsuspected trade-offs between costs and benefits of increasing density under changing environments. Previous generalizations about the importance of high density for reproductive success have so far remained robust, but such trade-offs could have unpredictable consequences for future population dynamics.

Colonial breeding in birds is widely considered to benefit individuals through enhanced protection against predators or transfer of information about foraging sites. This view, however, is largely based on studies of seabirds carried out under favourable conditions. Recent breeding failures at many seabird colonies in the UK provide an opportunity to re-examine costs and benefits of coloniality under adverse conditions. Common guillemots Uria aalge are highly colonial cliff-nesting seabirds with very flexible parental care. Although the single chick is normally never left alone, more than 50 per cent of offspring were left unattended at a North Sea colony in 2007, apparently because poor conditions forced both parents to forage simultaneously. Contrary to expectation, unattended chicks were not killed by avian predators. Rather, although non-breeders and failed breeders sometimes provided alloparental care, unattended chicks were frequently attacked by breeding guillemots at neighbouring sites, often with fatal consequences. These results highlight a previously unsuspected trade-off between provisioning chicks and avoiding conspecific attacks, and indicate that understanding how environmental conditions affect social dynamics is crucial to interpreting costs and benefits of colonial breeding.

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Over the past decade, the number of biological records submitted by members of the public have increased dramatically. However, this may result in reduced record quality, depending on how species are promoted in the media. Here we examined the two main promotional approaches for citizen science recording schemes: flagship-species, using one charismatic species as an umbrella for the entire group (here, Harmonia axyridis (Pallas) for Coleoptera: Coccinellidae); and general-group, where the group is promoted as a whole and no particular prominence is given to any one species (here, bumblebees, genus Bombus (Hymenoptera: Apidae)). Of the two approaches, the general-group approach produced data that was not biased towards any one species, but far fewer records per year overall. In contrast, the flagship-species approach generated a much larger annual dataset, but heavily biased towards the flagship itself. Therefore, we recommend that the approach for species promotion is fitted to the result desired.

Word count: 6,274 12 13 14 2 Reintroductions aim to re-establish species within their historical ranges through the release of wild-15 or captive-bred individuals following extirpation (or extinction) in the wild. While there is no general 16 agreement on what constitutes a successful reintroduction, the probability of the population achieving 17 long-term persistence should be addressed. Here, we review a 10-year trial reintroduction of the great 18bustard Otis tarda, a globally-threatened bird species, to the UK and assess long-term population 19 viability. Despite changes in rearing and release strategy, initial post-release survival probability 20 remained consistently low, with only 11.3% of bustards (n = 167) surviving from release to one year 21 post-release. Nineteen breeding attempts were made by eight females; however, only one chick 22 survived more than 100 days from hatching, and no wild juveniles have recruited into the population. 23Using demographic rates from the UK population and wild populations elsewhere and stochastic 24 population modelling, we investigate the viability of this reintroduced population by predicting 25 population size over the next ten years. Under current demographic rates the population was predicted 26 to decline rapidly. Self-sufficiency was only predicted using the highest estimates from the UK 27 population both for first-year and adult survival, and recruitment rates from wild populations 28 elsewhere. Although changes have been made in rearing, release strategies, habitat management and 29 release sites used, these changes appear to have modest impact on long-term viability. Substantial 30 improvements in survival rates and productivity are required in order to establish a viable great 31 bustard population in the UK, and we consider this unlikely. 32 33

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Pollinating insects provide pollination services to many crop species, including sweet cherry (Prunus avium L.), and this can be delivered by both managed and wild pollinators. Managed pollinators are often used to pollinate a range of fruit crops, but increasingly the role of wild insects is being studied. However, the importance of pollinator species depends on their relative abundance and pollination effectiveness, which depends on their foraging activity and their variability throughout the day. In this study, insect visitors of blossoms were observed in commercial sweet cherry orchards to explore abundance, diversity and pollination foraging behaviour of different insect pollinator groups throughout the day. A total of 1,174 pollinators from 31 different species were recorded visiting cherry blossoms over 2 years, of which 71.0% of total visits were by managed pollinators (western honeybee, Apis mellifera L. and buff‐tailed bumblebee, Bombus terrestris L.) compared to 29.0% by wild pollinators. On average, solitary bees visited a sweet cherry blossom for the longest duration (20.7 (±2.0 SE) seconds), whereas wild queen bumblebees visited the greatest number of flowers per minute (mean of 19.0 (±1.3 SE)). As both these pollinator groups contacted cherry stigmas more often and moved more frequently between tree rows than managed bees and hoverflies, they are more likely to facilitate cross‐pollination. The different pollinator groups also showed variation in behavioural parameters throughout the day, but less variation was recorded when all pollinator groups were considered altogether. This suggests diverse pollinator communities might be expected to provide a more stable pollination service to sweet cherry. This study demonstrates that whilst cherry blossoms were more frequently visited by managed pollinators, wild solitary bee and bumblebee behaviours are likely to be more effective at enhancing pollination in sweet cherry orchards, which, in turn, might lead to increased yields.