Three birds rendered as simplified SVG shapes—a grey circle for the body and two black paths for wings—flap in place within an 800-by-600 viewport. D3 transitions with `transition.attrTween` and `d3.interpolateString` alternate wing rotation between -45 and 45 degrees in a continuous loop, triggered recursively via the `on('end')` listener. The animation runs directly from a plain HTML file using D3 v6 and raw JavaScript, with no external data source; the birds are positioned at fixed coordinates (200,200), (400,300), and (400,150) and flap independently.