a responding call signal that is heard by the original frog. This finding means that D. ebraccatus males compete on many fronts during chorusing. They compete to find the best territory for producing calls that are heard over their competitors and for space where they themselves can receive calls. However, they can also compete to produce calls that are heard over others by adjusting their own call intensity in respect to surrounding aggressive calls. Males increase the aggressiveness of their calls when they have more competitors and when the aggressiveness of surrounding stimuli increases. Males decrease aggressive call intensity when there are a fewer number of competitors (or stimuli) and when surrounding calls have lower levels of aggressiveness. Group Living The common night call pattern of male chorus frog species is initially high aggressive call levels followed by a “stable chorus” with little to no aggressive calling. This pattern is due to habituation, the increase of aggressive thresholds in response to repeated calls greater than their original threshold. In contrast with most frog chorus species, a large fraction of D. ebraccatus males still make aggressive calls throughout the night with only a slight decrease. The continued aggressive calls throughout the night in this species indicates that D. ebraccatus males do not habituate in response to aggressive calls and instead are sensitized. In other words, these frogs initially decrease their aggressive threshold after exposure to repeated calls above threshold. This mechanism leads to more frequent aggressive calls than other chorus frogs. Anuran species that display chorus behaviors use aggressive calls as a mechanism to defend territory from other males, so it was not known for a while why high calling rates that expose male hourglass tree frogs to dangerous situations is maintained. One possible reason for high aggressive calling levels is that D. ebraccatus aggressive and advertisement thresholds are initially equal, and they need to decrease their aggressive threshold in order to be able to distinguish and respond to these distinct call types. Generally, there is a 210 millisecond response time frame that males take to respond to one call with a call of their own. The only exception to this 210 millisecond time frame is when male frogs are making the decision to switch to aggressive calls. The male frogs seem to respond with their first aggressive call more slowly due to trying to distinguish an advertisement call from an