Australian raven blue black carrion eaters corvids corvus coronoides garbage collectors loud mournful omnivorous predators raven scavengers shiny black Australian-raven beak bearded bill black blue-black carrion-eaters corvus-coronoides crow foraging garbage-collectors grass ravens sharp-eyed shiny-black strong bare bare branches branches lone perched perching tree bare wires danger electrical electrical power electrical wires electricity power power lines power pole wiring