I remember that my children and I marveled at the massive numbers of crows roosting in tall trees in the Rockville area of Montgomery County, Maryland in the late 1980s and through the 1990s. Then in the 2000s West Nile virus swept through the county and the trees were empty. The experience left us feeling a real sense of loss. Now I live in the Allegheny Highlands in a rural wooded area. There are crow families around, and we do have several dozen turkey vultures who come in to roost in the tall pine trees each winter. But I have yet to spot a crow roost. I'll have to look harder.
I was struck by the longevity of the crows and the steadfastness of the researchers over many years. It also surprised me that the researchers could examine baby crows so thoroughly, with such a variety of procedures, and then return them to the nest to pursue life as a nestling unperturbed. I wonder if the encounters and procedures remain in the birds' memories or affect their future behavior in any discernible way. In later years do they talk to each other about having been kidnapped by aliens...?