de facto
I suspect latetonight might me alluding to the fact that on some aircraft the Wx radar does indeed fire up, whether you've selected it on or not, at some point v. early in the take-off roll ( on the 777 the radar begins scanning once the thrust levers go into the take-off range)...you don't get weather returns displayed on the ND's if you've left the switch off, but nevertheless the radar is scanning and radiating to provide Predictive Windshear....and on the triple PWS alerts become active 12 seconds after the scanning begins.
That said I don't believe for one moment that the birds dive for cover because of the radar...