Both Prey and Predator Features Determine Predation Risk and Survival of Schooling Prey

Predation is one of the main evolutionary drivers of social grouping. While it is well appreciated that predation risk is likely not shared equally among individuals within groups, its detailed quantification has remained difficult due to the speed of attacks and the highly-dynamic nature of collective prey response. Here, using high-resolution tracking of solitary predators (Northern pike) hunting schooling fish (golden shiners), we not only provide detailed insights into predator decision-making but show which key spatial and kinematic features of predator and prey influence individual's risk to be targeted and survive attacks. Pike tended to stealthily approach the largest groups, and were often already inside the school when launching their attack, making prey in this frontal "strike zone" the most vulnerable to be targeted. From the prey's perspective, those fish in central locations, but relatively far from, and less aligned with, neighbours, were most likely to be targeted. While the majority of attacks (70%) were successful, targeted individuals that did manage to avoid capture exhibited a higher maximum acceleration response just before the attack and were further away from the pike's head. Our results highlight the crucial interplay between predators' attack strategy and response of prey in determining predation risk in mobile animal groups.

Consensus of travel direction is achieved by simple copying, not voting, in free-ranging goats

For group-living animals to remain cohesive they must agree on where to travel. Theoretical models predict shared group decisions should be favoured, and a number of empirical examples support this. However, the behavioural mechanisms that underpin shared decision-making are not fully understood. Groups may achieve consensus of direction by active communication of individual preferences (i.e. voting), or by responding to each other's orientation and movement (i.e. copying). For example, African buffalo ( Syncerus caffer ) are reported to use body orientation to vote and indicate their preferred direction to achieve a consensus on travel direction, while golden shiners ( Notemigonus crysoleucas ) achieve consensus of direction by responding to the movement cues of their neighbours. Here, we present a conceptual model (supported by agent-based simulations) that allows us to distinguish patterns of motion that represent voting or copying. We test our model predictions using high-resolution GPS and magnetometer data collected from a herd of free-ranging goats ( Capra aegagrus hircus ) in the Namib Desert, Namibia. We find that decisions concerning travel direction were more consistent with individuals copying one another's motion and find no evidence to support the use of voting with body orientation. Our findings highlight the role of simple behavioural rules for collective decision-making by animal groups.

Validation of Annulus Formation in Golden Shiner Otoliths

Golden Shiner Notemigonus crysoleucas is found in many lakes and ponds across the southeastern United States. Though it is a common species, otolith age validation methods have not been published. The objective of this study was to confirm annulus formation in lapillar otoliths of Golden Shiners collected monthly from September 2015 through August 2016 in Lake Jackson, Florida (Leon County). We collected at least 12 individuals each month of similar length (168–249 mm; presumably of the same cohort) to document annulus formation throughout the year. We sacrificed a total of 177 individuals from the 2013 year class, and we used their lapillar otoliths for marginal incremental analysis to calculate an index of completion and validate annulus formation. The monthly index of completion was highest from January through March and lowest in May and June, indicating that annuli were deposited once per year and confirming that lapillar otoliths are a valid age estimation structure for Golden Shiners.