Communication between social animals is critical for survival. American crows (Corvus brachyrhynchos) form large, often raucous social aggregations. Our previous research has suggested that crow calls have context-dependent differences in the durations of silence between syllables, i.e. gaps. Specifically, we found that longer gap durations were associated with pre-roost aggregations, which are assemblies of crows formed before heading to their nightly roosts. However, other research found that continually decreasing gap durations throughout calls led to the most assembly behavior in this species. Our work tests the hypothesis that crows will show different assembly behavior in response to crow calls artificially constructed to vary in gap duration. We created modified crow calls using recordings of crows made in the wild, shortened the gap durations across trial groups, and played these modified calls back to crows in diurnal activity centers - areas where crows forage during the day - across eight different locations using a repeated measures design. We recorded the number of crows within 0-5, 5-15, 15-30, and 30-50 meters of the speaker every 3 minutes during 30 minutes of call playback at each location. We also recorded the closest approach to the speaker and total vocalizations made. No significant differences were found across these variables; suggesting that calls with decreasing gap durations do not elicit more assembly. Because we saw some evidence of habituation during these tests, we decided to conduct a follow up study in which we no longer use a repeated measures approach, and change locations after every trial. We also altered our playback methods to include overlapping calls, which we often hear from crows in the field, in hopes that this would elicit more assembly. Early tests suggest these new approaches are more successful in generating assembly behavior.