Subtle cues of predation risk: starlings respond to a predator's direction of eye-gaze

For prey animals to negotiate successfully the fundamental trade-off between predation and starvation, a realistic assessment of predation risk is vital. Prey responses to conspicuous indicators of risk (such as looming predators or fleeing conspecifics) are well documented, but there should also be strong selection for the detection of more subtle cues. A predator's head orientation and eye-gaze direction are good candidates for subtle but useful indicators of risk, since many predators orient their head and eyes towards their prey as they attack. We describe the first explicit demonstration of a bird responding to a live predator's eye-gaze direction. We present wild-caught European starlings (Sturnus vulgaris) with human 'predators' whose frontal appearance and gaze direction are manipulated independently, and show that starlings are sensitive to the predator's orientation, the presence of eyes and the direction of eye-gaze. Starlings respond in a functionally significant manner: when the predator's gaze was averted, starlings resumed feeding earlier, at a higher rate and consumed more food overall. By correctly assessing lower risk and returning to feeding activity earlier (as in this study), the animal gains a competitive advantage over conspecifics that do not respond to the subtle predator cue in this way.     

Electrophysiological Correlates of Vigilance During a Continuous Performance Test in Healthy Adults

The present study evaluated patterns of electrophysiological activity associated with sustained vigilance in healthy adults. Quantitative electroencephalographs (QEEG) were recorded during the performance of a Continuous Performance Test (CPT). Participants were divided into low and high vigilance groups based upon their reaction time changes between the early and late portions of the CPT. Coherence measures were calculated from the QEEG across the baseline, early CPT, and late CPT experimental conditions. Participants in the low vigilance group had higher baseline and CPT frontal to posterior coherence in the alpha and beta bands suggestive of a less vigilant state throughout the entire study. Additionally, the low vigilance group had a significantly greater beta 1 band coherence drop from baseline to the initial portion of the CPT than the high vigilance group. The combined groups had significantly lower amounts of right hemisphere frontal to posterior coherence across a number of frequency bands throughout all of the phases of the study when compared to the homologous left hemisphere sites. These interhemispheric coherence differences are consistent with vigilance network theories that implicate the right frontal and parietal lobes in the maintenance of sustained attention (M. I. Posner & M. E. Raichle, 1994).     

Increased vigilance of paired males in sexually dimorphic species: distinguishing between alternative explanations in wintering Eurasian wigeon

In animal pairs, males are often more vigilant than females.This is generally assumed to result from mate guarding (eitheragainst predators or other males). However, when males haveconspicuous secondary sexual characteristics, they could beconstrained to be more vigilant because of a higher predationrisk than females. We attempted to distinguish between the "maleconstraint hypothesis" and two variations of the mate-guardinghypothesis by studying the vigilance behavior of the sexuallydimorphic wigeon during early winter, when some males are inbreeding plumage and some are not and when not all males arepaired. The proportion of time spent vigilant by paired malesin breeding plumage was five times higher than any other categoryof males or females. We found no significant differences betweenthe vigilance levels of unpaired male wigeon in cryptic andin breeding plumage and therefore rejected the male constrainthypothesis. As vigilance levels of paired and unpaired femalesdid not differ either, we rejected the hypothesis that pairedmales invest in vigilance to reduce their mate's need to bevigilant to predation risks. Paired females interacted lessfrequently with other wigeon than unpaired ones, and it is probablyto protect their female from other males that paired male wigeonincrease their vigilance times.     

Why Be Vigilant? The Case of the Alpha Animal

We compared patterns of vigilance behavior in a male- and a female-dominant species—white-faced capuchins and ring-tailed lemurs—and used the results to test four hypotheses to explain vigilance behavior in primates. Adult male white-faced capuchins spent significantly more time vigilant than females did, and much male vigilance appeared to be directed toward males from other social groups. This finding supports the protection of paternity hypothesis. No sex difference existed in vigilance behavior among the ring-tailed lemurs, and subjects of both sexes exhibited more vigilance toward predators/potential predators than toward extragroup conspecifics, which supports the predator detection hypothesis. A trade-off argument, suggesting that females tolerate males in a group in return for greater male vigilance, does not apply to ring-tailed lemurs in our study. In both the male-dominant capuchins and the female-dominant ring-tailed lemurs, the alpha subject in the majority of the study groups was significantly more vigilant than other group members were. In white-faced capuchins, the alpha male mates more often than subordinate males do; therefore, the greater degree of vigilance exhibited by the alpha male may correspond to the protection of his reproductive investment. In ring-tailed lemurs, there can be more than one matriline in a group. Thus, the greater amount of vigilance behavior exhibited by the alpha female may be related to protection of her matriline, which could ultimately lead to greater inclusive fitness. Alpha subjects in our study groups exhibited certain behaviors more frequently or exclusively. Accordingly, there may be a constellation of behaviors characteristic of alpha animals.     

Conspecific Influences on Vigilance Behavior in Wild Chimpanzees

Diurnal primates rely on visual monitoring behavior to collect various kinds of ecological and social information. Vigilance behavior is monitoring specifically to detect external threats. Previous studies of vigilance behavior were focused mainly on the influence of predation threats, whereas the influences of conspecific factors, such as intragroup threats, have been relatively unstudied. Individual vigilance is predicted to be inversely related to the group size or the number of individuals nearby if the main target of the vigilance is a predation threat and positively related if the main target of the vigilance is a conspecific threat. I studied wild chimpanzees (Pan troglodytes schweinfurthii) in Mahale Mountains National Park, Tanzania, and measured the vigilance duration when they are resting on the ground via 2-min focal observation. In both males and females, vigilance duration increased as the number of individuals nearby increased. This result agrees with the idea that the chimpanzees are vigilant toward other group members. In addition, maternal vigilance monitors and protects the safety of dependent offspring as the duration of maternal vigilance was longer when a dependent infant was separated from its mother than when the offspring was in contact with its mother. The results indicate that the vigilance behavior in wild chimpanzees was affected by conspecific factors.     

Niche expansion of a cryptic primate, Callimico goeldii, while in mixed species troops

We examined the effects of polyspecific associations on the behavior of one group of Callimico goeldii in northwestern Bolivia. Data were collected for 1 year using focal animal sampling at 5-min intervals, for a total of 1,375 observation hours. In total, C. goeldii formed mixed species troops with five groups of Saguinus fuscicollis and six groups of S. labiatus, and these were maintained during 81% of observations. C. goeldii rested more and traveled less while alone than while associated, but neither vigilance behavior in the understory nor habitat use were affected by association status. The composition of the group's diet was different while alone (higher in structural carbohydrates [fungi] and lower in simple sugars [ripe fruits] and protein [insects]) than while associated (fungi 65 vs. 37%; fruits 13 vs. 32%; insects 5 vs. 15%). We propose therefore, that C. goeldii has a lower quality and more narrowly based diet while alone as compared to while associated. The factors that allow for this dietary expansion while in mixed species troops require further investigation.     

Mating system variation and morph fluctuations in a polymorphic lizard

In polymorphic male painted dragon lizards (Ctenophorus pictus), red males win staged contests for females over yellow males, and yellow males have greater success in staged sperm competition trials than red males. This predicts different reproductive strategies in the wild with red males being more coercive or better mate guarders than yellow males. Yellow males would be expected to sire more offspring per copulation and have a greater proportion of offspring from clutches with mixed paternity. However, here we show using microsatellites that the frequency of mixed paternity in the wild is low (< 20% on average across years), that all morphs on average have the same number of offspring sired per year, and that mating system variation (polyandry vs. monandry) is strongly correlated with perch density on male territories. Furthermore, a logistic regression on male successful vs. unsuccessful mate acquisition showed that red males were under negative selection when they dominated the population, which suggests ongoing frequency dependent selection on male colouration.     

Do Yellow‐Bellied Marmots Perceive Enhanced Predation Risk When they are Farther from safety? An experimental study

Whereas there are many studies of the time allocated to antipredator vigilance while animals forage, the vast majority of these studies remain correlative. This is potentially problematic because a variety of factors other than variation in perceived risk might influence putative antipredator behaviors such as time allocated to vigilance and foraging. We conducted an experimental study of yellow‐bellied marmot (Marmota flaviventris) antipredator behavior while marmots foraged at a replicated set of feeding stations established 1, 5, 10, and 20 m from their main burrows. Marmots appeared to perceive a reduced risk of predation when they foraged in the presence of other marmots; they allocated more time to foraging and decreased the time allocated to vigilance. When they foraged farther from their burrows, marmots initiated foraging after a substantially greater amount of time, tended to increase the frequency of their bouts of vigilance, and decreased the duration of each bout. Yearling marmots took less time to begin foraging than adults. Marmot flight initiation distance at our feeding trays was independent of the distance they foraged away from the burrow. Taken together, these experimental results demonstrate that marmots' perceptions of risk increased with distance to the burrow and decreased when other individuals were within 10 m of them while they foraged.