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