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International audience; Saproxylic beetles may act as bio-indicators of high-quality mature woodlands, and their conservation is strongly linked to the quality and quantity of deadwood in a biotope. We tested the effect of deadwood accumulation and habitat variables on saproxylic species richness by investigating six sampling sites under different deadwood management practices that belong to both alluvial and riparian mixed forests of the Po plain, Italy. We sampled 43 obligate saproxylic species. The main factor predicting saproxylic species richness was the amount of deadwood measured by both log diameter and volume. We found a threshold of 0.22 m diameter (confidence interval CI 0.18-0.37 m) and 32.04 m3/ha volume (CI 16.09-64.09 m3/ha) below which saproxylic beetle richness would be significantly reduced and a threshold of 35 m3/ha dead wood volume (CI 33-40 m3/ha) over which species richness increases by\5 %. The other deadwood and environmental components influenced saproxylic beetle richness to a lesser extent; some of them, however, should still be considered for proper management. Forest structure variables describing forest density such as large trees and basal areas have a negative effect on species richness. According to the results of our study, stumps and advanced decaying class are positively correlated, while small logs are negatively correlated to species richness. Thus, in extensively managed forests, the regular cutting of trees should be implemented to create artificial stumps, in order to assure a continuity of deadwood and, in the meantime, increase the number and width of openings in the forest. Moreover, prolonging rotation times can assure the presence of deadwood at intermediate/later stages of decay.

International audience; Numerous studies have investigated the remarkable variation of social features and the resulting structures across species. Indeed,relationships are dynamic and vary in time according to various factors such as environmental conditions or individuals attributes.However, few studies have investigated the processes that stabilize the structures within a given species, and the behaviouralmechanisms that ensure their coherence and continuity across time. Here, we used a dynamic actor-based model, RSiena, toinvestigate the consistency of the temporal dynamic of relationships of a group of captive rooks facing recurrent modifications ingroup composition (i.e. the loss and introduction of individuals). We found that changes in relationships (i.e. formation andremoval) followed consistent patterns regardless of group composition and sex-ratio. Rooks preferentially interacted with pairedcongeners (i.e. unpopular attachment) and were more likely to form relationships with individuals bonded to a current socialpartner (i.e. “friends of friends”, or triadic closure). The sex of individuals had no effect on the dynamic of relationships. Thisrobust behavioural mechanisms formed the basis of inter-connected networks, composed of sub-structures of individualsemerging from the enmeshment of dyadic and triadic motifs. Overall, the present study reveals crucial aspects of the behaviouralmechanisms shaping rooks social structure, suggesting that rooks live in a well-integrated society, going far beyond the uniquemonogamous pair-bond.

A commentaryon:Foraging Bumble Bees Weigh the Reliability of Personal and Social Informationby Dunlap,A.S.,Nielsen,M.E.,Dornhaus,A.,andPapaj,D.R.(2016).Curr.Biol.26,1195–1199.doi: 10.1016/j.cub.2016.03.009Copy-when-uncertain:bumble bees rely on socia information when rewards are highly variableby Smolla,M.,Alem,S.,Chittka,L.,andShultz,S.(2016).Biol.Lett.12:20160188.doi:10.1098/rsbl.2016.0188; International audience; Group-living animals often use social information, in addition to personal sampling, to learn about foraging opportunities. Small-brained insects are no exception (Grüter and Leadbeater, 2014). For instance, inexperienced bumblebees learn to identify profitable flower species by observing conspecifics (Leadbeater and Chittka, 2005). Bumblebees are especially suitable to study insect social learning as they can be easily tested in the lab, allowing for precise control of food resources, individual experience and social cues (Avarguès-Weber et al., 2015). Here we comment on two recent studies showing how bumblebees use personal and social information discriminately to make adaptive foraging decisions, thus setting the scene for complex social foraging dynamics among bees exploiting variable ressources in the field. Writing in Current Biology, Dunlap et al. (2016) report that foragers of the common eastern bumblebee (Bombus impatiens) rely more on social information than on personal information if the former predicts a reward. The authors trained bumblebees to collect sucrose solution in arrays of 12 artificial flowers in which they manipulated personal information (by using yellow or orange flowers) and social information (by marking some flowers with a pinned dried conspecific). During training, each type of information was either fully reliable (100% of flowers rewarded), moderately reliable (83% of flowers rewarded), or unreliable (50% of flowers rewarded) in a full factorial design of nine treatments. Bumblebees were equally successful at associating personal and social information to a reward. However during the test, in which only unrewarded flowers of all four types were used, most bumblebees preferred flowers with a conspecific. For treatments in which social information was moderately or highly reliable, bumblebees always preferred flowers with a conspecific, even if personal information was more reliable. When both information were unreliable, bumblebees did not show any preference. Only, when social information was unreliable and personal information moderately or highly reliable, bumblebees preferred flowers without a conspecific. In another study published in Biology Letters, Smolla et al. (2016) show that buff-tailed bumblebees (Bombus terrestris) rely on social information when personal information is unreliable.