A Harrier is any of several species of diurnal birds of prey which fly low over meadows and marshes and hunt or harry small animals or birds (hence their common name). Most are in the genus Circus, the scientific name also arising from from the slow circling for prey.

The northern hemisphere species are:

• Western Marsh Harrier Circus aerunginosus and Eastern Marsh Harrier, Circus spilonotus, both described under Marsh Harrier
• Hen Harrier or (US) Northern Harrier (Circus cyaneus)
• Pallid Harrier (Circus macrourus)
• Montagu's Harrier (Circus pygargus)

The American Northern Harrier is also known as the Marsh Hawk. It is usually classed as conspecific with the Hen Harrier, but is sometimes considered a separate species.

South African species are:

• Western Marsh Harrier or Eurasian Marsh Harrier (Circus aeruginosus)
• African Marsh Harrier (Circus ranivorus)
• Black Harrier (Circus maurus)
• Pallid Harrier (Circus macrourus)
• Montagu's Harrier (Circus pygargus)

Australasian species are:

• Spotted Harrier (Circus assimilis)
• Swamp Harrier (Circus approximans), sometimes also called the New Zealand Harrier.

Species list

• ORDER FALCONIFORMES
• Family Accipitridae
  • Subfamily Elaninae
  • Subfamily Perninae
  • Subfamily Milvinae
  • Subfamily Accipitrinae
  • Subfamily Buteoninae
  • Subfamily Aegypiinae: old world vultures
  • Subfamily Circinae: harriers
    • Montagu's Harrier, Circus pygargus
    • Northern Harrier, Circus cyaneus
    • Western Marsh Harrier, Circus aeruginosus
    • Eastern Marsh Harrier, Circus spilonotus
    • African Marsh Harrier, Circus ranivorus
    • Swamp Harrier, Circus approximans
    • Madagascar Marsh Harrier, Circus maillardi
    • Long-winged Harrier, Circus buffoni
    • Spotted Harrier, Circus assimilis
    • Black Harrier, Circus maurus
    • Cinereous Harrier, Circus cinereus
    • Pallid Harrier, Circus macrourus
    • Pied Harrier, Circus melanoleucos
    • Madagascar Harrier-hawk, Polyboroides radiatus
    • African Harrier-hawk, Polyboroides typus
    • Crane Hawk, Geranospiza caerulescens
  • Subfamily Circaetinae: snake-eagles