We conducted two experiments comparing communication behaviors of co-located users in collaborative augmented reality (AR) interfaces. In the first experiment, we compared optical, stereo- and mono-video, and immersive head mounted displays (HMDs) using a target identification task. It was found that differences in the real world visibility severely affect communication behaviors. The optical see-through case produced the best results with the least extra communication needed. Generally, the more difficult it was to use non-verbal communication cues, the more people resorted to speech cues to compensate. In the second experiment, we compared three different combinations of task and communication spaces using a 2D icon designing task with optical see-through HMDs. It was found that the spatial relationship between the task and communication spaces also severely affected communication behaviors. Placing the task space between the subjects produced the most active behaviors in terms of initiatory body languages and utterances with least miscommunications.