The dances of the European honeybee are often cited as an animal communication system. Scout bees returning to the hive indicate the location and extent of a food source using characteristic dances. Ants use chemical secretions called pheromones for communication. There may be as many as ten different secretions/message complexes in an ant’s repertoire. Simple carbon dioxide, for example, promotes clustering for working on larger tasks. Each colony has a unique odor that identifies it and its members. This separates neighbors from intruders. Likewise, foraging ants secrete special pheromones along the trail when returning food to the colony. The density of these trails acts a strong recruiting agent for other ants to follow. High-density trails are more impelling than lower density. As the food supply wanes (i.e., fewer returning foragers), the number of ants recruited naturally dwindles. Birdcalls have been identified as signaling the presence of predators. The calls are different depending upon whether the threat is from below or above.