These fledgling juveniles were begging for food on the roof of a building. The "gape flanges" are clearly visible. These are the yellow edges to the base of the bill which outline the mouth lining and provide a target for the adult. It is believed that the combination of yellow gape flange and yellow-orange mouth lining stimulates the adult birds to feed their babies.
Feeding was accomplished at lightning speed, with the adults remaining in flight rather than landing. This lower photo was the only shot I was able to get of actual feeding.
North American breeding birds are the subspecies H. r. erythrogaster, characterized by their reddish belly. Eurasian populations usually have the belly white.
Digiscoped with Panasonic DMC-LZ5 | Nikon FieldScope III | 30XWA | hand-held (no adapter)