Three-dimensional trajectories and network analyses of group behaviour within chimney swift flocks during approaches to the roost

Chimney swifts ( Chaetura pelagica ) are highly manoeuvrable birds notable for roosting overnight in chimneys, in groups of hundreds or thousands of birds, before and during their autumn migration. At dusk, birds gather in large numbers from surrounding areas near a roost site. The whole flock then employs an orderly, but dynamic, circling approach pattern before rapidly entering a small aperture en masse . We recorded the three-dimensional trajectories of ≈1 800 individual birds during a 30 min period encompassing flock formation, circling, and landing, and used these trajectories to test several hypotheses relating to flock or group behaviour. Specifically, we investigated whether the swifts use local interaction rules based on topological distance (e.g. the n nearest neighbours, regardless of their distance) rather than physical distance (e.g. neighbours within x m, regardless of number) to guide interactions, whether the chimney entry zone is more or less cooperative than the surrounding flock, and whether the characteristic subgroup size is constant or varies with flock density. We found that the swift flock is structured around local rules based on physical distance, that subgroup size increases with density, and that there exist regions of the flock that are less cooperative than others, in particular the chimney entry zone.

Watch out or relax: conspecifics affect vigilance in wild spider monkeys (Ateles geoffroyi)

In most animal species, predation risk is considered the main factor affecting vigilance, and an individual is expected to spend less time vigilant in larger than in smaller groups. However, vigilance patterns in primates appear to differ, with no consistency in group-size effects. As individuals in highly gregarious species such as diurnal primates face frequent threats from group members, there may be increased vigilance in larger groups to monitor conspecifics rather than or in addition to predators. We tested this hypothesis in wild spider monkeys, which live in communities but fission and fuse in subgroups of variable size and membership throughout the same day. We found no overall effect of subgroup size, as traditionally measured, on vigilance. However, a possible explanation is that vigilance may be effectively shared only with individuals in close proximity, rather than with all subgroup members. We found that a larger number of neighbours (i.e., subgroup members within 5 m) was associated with a lower proportion of time individuals spent vigilant, which is similar to findings in other studies. Another social factor that may affect individuals’ vigilance is the possibility of between-community encounters. Higher levels of vigilance can be expected in areas closer to the boundary of the home range, where between-community encounters are more likely to occur compared with non-boundary areas. We found that location in terms of boundary vs. non-boundary areas had a significant effect on the time individuals spent vigilant in the expected direction. We also found that location modulated the effect of subgroup size on vigilance: only in the boundary areas did larger subgroup sizes result in less individual vigilance time. We concluded that conspecifics affect vigilance of wild spider monkeys in multiple ways.

Are More Stringent NCLB State Accountability Systems Associated With Better Student Outcomes? An Analysis of NAEP Results Across States

This study developed a comprehensive measure of the stringency level of NCLB states’ accountability systems, including the strength of their annual measurable objectives, confidence intervals, performance indexing, retesting, minimum subgroup size, and the difficulty levels of proficiency standards. This study related accountability stringency in 2003 to student achievement and achievement gaps on NAEP math and reading tests from 2003 and 2005. The results were inconsistent across grades, subjects, and ethnic groups. An increase in accountability stringency, such as requiring faster progress, not allowing for retesting, and allowing a smaller minimum subgroup size were related to improved math achievement for fourth-grade Hispanic students. Not using confidence intervals was related to higher math and reading achievement for White and Hispanic students. However, accountability stringency did not have any positive effects and even negative effects on eighth-grade Black students.