Is there any explanation for this sad phenomenon?
From orf.at:
USA: Around 1,000 birds hit windows and died
Around 1,000 birds crashed into the windows of a convention center in Chicago in one night and died. This is an exceptionally high number, several US media reported yesterday (local time).
Highest documented number in the past 40 years
True, such tragedies occur every year, especially during the autumn and spring migration of migratory birds. In the past 40 years, Chicago's Field Museum of Natural History has never documented such a high number, the institution wrote yesterday on Instagram. “It was just frustrating,” bird expert David Willard told the Chicago Tribune newspaper.
“You see a rose-breasted grosgrain that would have made it to the Peruvian Andes if it hadn't flown into a window in Chicago.” He cited, among other things, the illuminated windows of the convention center and unfavorable weather conditions as possible reasons for the incident.
Rain and warm temperatures delayed the migration of the birds, then they all started at the same time, CBS reported. This is also why there were a particularly large number of migratory birds in the area, explained Douglas Stotz from the Field Museum to CBS.