Enduring positive social bonds between individuals are crucial for humans' health and well being. Similar bonds can be found in a wide range of taxa, revealing the evolutionary origins of humans' social bonds. Evidence suggests that these strong social bonds can function to buffer the negative effects of living in groups, but it is not known whether they also function to minimize predation risk. Here, we show that crested macaques (Macaca nigra) react more strongly to playbacks of recruitment alarm calls (i.e. calls signalling the presence of a predator and eliciting cooperative mobbing behaviour) if they were produced by an individual with whom they share a strong social bond. Dominance relationships between caller and listener had no effect on the reaction of the listener. Thus, strong social bonds may improve the coordination and efficiency of cooperative defence against predators, and therefore increase chances of survival. This result broadens our understanding of the evolution and function of social bonds by highlighting their importance in the anti-predator context.

Intense trapping of the critically endangered Yellow-crested Cockatoo (Cacatua sulphurea) for the international pet trade has devastated its populations across Indonesia such that populations of >100 individuals remain at only a handful of sites. We combined distance sampling with density surface modeling (DSM) to predict local densities and estimate total population size for one of these areas, Komodo Island, part of Komodo National Park (KNP) in Indonesia. We modeled local density based on topography (topographic wetness index) and habitat types (percentage of palm savanna and deciduous monsoon forest). Our population estimate of 1,113 (95% CI: 587–2,109) individuals on Komodo Island was considerably larger than previous conservative estimates. Our density surface maps showed cockatoos to be absent over much of the island, but present at high densities in wooded valleys. Coincidence between our DSM and a set of independent cockatoo observations was high (93%). Standardized annual counts by KNP staff in selected areas of the island showed increases in cockatoo records from <400 in 2011 to ~650 in 2017. Taken together, our results indicate that KNP, alongside and indeed because of preserving its iconic Komodo dragons (Varanus komodoensis), is succeeding in protecting a significant population of Indonesia’s rarest cockatoo species. To our knowledge this is the first time DSM has been applied to a critically endangered species. Our findings highlight the potential of DSM for locating abundance hotspots, identifying habitat associations, and estimating global population size in a range of threatened taxa, especially if independent datasets can be used to validate model predictions.

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Large introduced mammalian herbivores, either as livestock or feral populations, can have important effects on vegetation and animals. Introduced herbivores can be of high conservation concern if they impact threatened native species in protected areas. We evaluated temporal and spatial trends in the relative abundance of introduced water buffalo (Bubalus bubalis) and their potential to induce competition-related ecological and demographic effects on native rusa deer (Rusa timorensis) in Komodo National Park and the Wae Wuul Nature Reserve-two protected areas in Eastern Indonesia. To monitor ungulate population abundances and population growth rates of water buffalo and rusa deer, we counted their dung (a validated abundance index in these two species) along 350 permanently marked transects at 11 sites over five islands annually between 2003 and 2018. Water buffalo dung abundance varied with the site, year and their interaction. Water buffalo dung was most abundant within the Wae Wuul Nature Reserve, and their dung abundance varied considerably among sites in Komodo National Park. Water buffalo site-specific dung abundances fluctuated independently over time. In areas of high water buffalo dung densities, rusa deer altered resource use and had lower population densities than sites without water buffalo. Rusa deer dung-based population growth rates were negatively influenced by density-dependent regulation and only weakly by water buffalo dung density. Currently, managers do not control water buffalo in either protected area. Nevertheless, the benefits of control could reduce water buffalo effects on vegetation composition, watercourse integrity, or the potential to transmit disease into native ungulates.