that increased its searching behavior in response to the distraction display of a grouse and eventually found and killed the grouse nestlings. Factors influencing decision Given these risks, an animal must decide when distraction display is an appropriate response to a predator. Researchers have found several important factors that appear to influence the decision to use a distraction display and the intensity of the display, although it is not evident that these factors are taken into consideration consciously by the displaying animal. Several considerations involving the predator have been shown to be important, including the distance of the predator from the nest. Intensity of display has been shown to decrease as the distance of the predator from the nest increases, perhaps representing the balancing of risk to the displaying parent and to the vulnerable young. The type of predator has also been shown to be of importance, with birds tending to display most intensely to ground-dwelling carnivores and less intensely to humans and flying predators. Finally, the number of potential predators has also been shown to be important in sticklebacks, in which frequency of distraction displaying by the male is positively correlated with the number of conspecifics in a foraging shoal. In addition, the presence of a second parent at the nest correlates with increased display intensity, perhaps representing a diluted predation risk. The number of potential extra-pair mobbers has also been shown to marginally increase the intensity of the display, again representing a possible dilution of risk to each of the animals engaging in the distraction. Third, the timing of distraction display as a correlate of nestling age has been a matter of particular interest in birds, with study results showing that the age at which displays are performed differs in species with precocial and altricial young. In species with precocial young, distraction display is most frequent just after hatching, while in altricial young, it is most frequent just before fledging. This may represent a greater tendency to display at the times when parental investment in young is greatest, and the young are still very vulnerable. However, some studies have failed to find any correlation between the cost of replacing a brood (a measure of parental investment) and the frequency of distraction display. Lastly, game theory has been employed to explain how grouse may decide to display or not based on proxies for the abundance of "smart" predators, such