This is a true miracle, not in the religious supernatural sense, but in the sense of miraculum (latin) a wonder, a marvel or amazing event.  Small birds often fly into large buildings: supermarkets, Home Depot, etc.  They usually avoid people down below and stay up near the ceiling and perch in a secluded space.  This sparrow in the midst of thousands of noisy people and while Bernie was speaking and waving his arms, as is his style,  was not afraid of him and actually came to him and perched on the lectern. This is unexpected and atypical behavior. Cynics may dismiss it, but there is more wonder in the universe than we know and Bernie has a spirit of truth and passion for justice and fairness that is very atypical, especially for someone running for the highest political office in the land.