There are four subspecies of yellow-rumped thornbill. Aphelocephala is a genus of bird in the thornbill family Acanthizidae. The yellow-rumped thornbill is the largest species of thornbill, long and weighing . Brown thornbill couples tend to pair for a long time. The brown thornbill ranges in size from , making it relatively small. The mean length of the small intestine is in the mistletoebird and in the thornbill. The mean length of the gizzard in the mistletoebird is and in the thornbill. The yellow-rumped thornbill is insectivorous; major prey items include ants, beetles, bugs and lerps. The western thornbill ("Acanthiza inornata") is a species of bird in the family Acanthizidae. The black-backed thornbill ("Ramphomicron dorsale") is a species of hummingbird in the family Trochilidae. The yellow-rumped thornbill ("Acanthiza chrysorrhoa") is a species of passerine bird from the genus Acanthiza. The rufous-capped thornbill ("Chalcostigma ruficeps") is a species of hummingbird in the family Trochilidae. The rainbow-bearded thornbill ("Chalcostigma herrani") is a species of hummingbird in the family Trochilidae. The purple-backed thornbill ("Ramphomicron microrhynchum") is a species of hummingbird in the family Trochilidae. The name "Acanthisitta" is a portmanteau of the thornbill genus "Acanthiza" and the genus "Sitta".