Environmental change is becoming synchronous across sites with frequent emergence of extremes in recent years, with alarming potential impacts on species’ synchronous abundance over large scales. With 23 years of breeding bird survey data across North America, we found that some birds are becoming synchronously rare across sites, while others are becoming synchronously common. We evaluated the relative importance of two co-occurring mechanisms (environment-driven and dispersal-driven) to explain such spatial synchrony in extreme low or high abundance (i.e., tail-dependent synchrony). We found that spatial synchrony in temperature extremes (i.e., tail-dependence in climate) was the major driver for birds’ tail-dependent spatial synchrony up to 250 Km. In addition, temperature extremes and dispersal trait both favored synergistically some species making them synchronously common across sites. In a rapidly changing environment, these findings highlight the importance of considering synchronized climatic extremes to assess species’ tail-dependent spatial synchrony across large scale.