two canada geese in flight against a blue sky

against anatidae animal avesl avian avifauna bif bill bird birding blue branta brantacanadensis brown cago canada canadensis chordata clear during ecology endothermic environment feather feathers flight flying fowl free geese goose homeothermic large migration natural neck ornithology pair sky tachymetabolic taicanadagoose vertebrate warmblooded watching water waterfowl webbedfeet white wild wildlife wings zoology