Synchronizing vigilance or taking turns as sentinels? The importance of testing coordination

Diurnal species can reduce the cost of the trade-off between feeding and predation risk by 1) performing low-quality (vigilance while performing another behavior) instead of high quality vigilance (only performing vigilance) or 2) by vigilance coordination either by taking turns acting as sentinels or by synchronizing vigilance bouts. A sentinel system assumes that sentinels are located at raised positions, alarm signal, and alternate vigilance bouts. However, many species with a described sentinel system have not been tested yet for coordination. We set out to study coordinated behavior and the reasons for this behavior in the invasive Barbary ground squirrel, Atlantoxerus getulus, using behavioral observations and genetic analyses. This species performs a type of vigilance (perch behavior) seemingly similar to sentinel behavior as individuals performed high-quality vigilance at raised locations for over 30 s, but alternating coordination is unknown. Perch behavior was coordinated but synchronized instead of taking turns (sentinel). Both sexes performed perch behavior and individuals performed perch behavior in the absence and presence of kin and offspring. We found that survival or time spent foraging did not decrease for perched individuals, nor that individual survival increased. Perch behavior in the invasive population of A. getulus may be synchronized 1) to perform an optimal activity when satiated (low costs), and, 2) may be an adaptation to habitat structure (large benefits). Our study demonstrates that the cost of the vigilance/foraging trade-off may not be high for invasive species and argued the importance of testing for coordination in species with described sentinel systems.