According to this story by Kevin Quealy in the New York Times, which has a very interesting map and graph, because of the coronavirus pandemic,
[r]oughly 5 percent of residents — or about 420,000 people — left the city between March 1 and May 1. In the city’s very wealthiest blocks, in neighborhoods like the Upper East Side, the West Village, SoHo and Brooklyn Heights, residential population decreased by 40 percent or more, while the rest of the city saw comparably modest changes.
As the next paragraph notes, “[s]ome of these areas are typically home to lots of students, many of whom left as colleges and universities closed.” The Heights does have a substantial student population.
The estimates of population loss by neighborhood were based on “an analysis of multiple sources of aggregated smartphone location data.”