Little bittern (Ixobrychus minutus)

Also known as: Australian little bittern, leech bittern, minute bittern
Synonyms: Ardea minuta
  
French: Blongios nain
KingdomAnimalia
PhylumChordata
ClassAves
OrderCiconiiformes
FamilyArdeidae
GenusIxobrychus (1)
SizeLength: 25 - 36 cm (2) (3)
Wingspan: 40 - 58 cm (2)
Weight59 - 150 g (2)

The little bittern is classified as Least Concern (LC) on the IUCN Red List (1).

The little bittern (Ixobrychus minutus) is, as its name suggests, a tiny heron species, most easily identified by its dark back, dark cap and buffy-white neck and wing patches, which contrast with the dark flight feathers, particularly during flight (3) (4). In the adult male little bittern, the crown is greenish-black and has elongated feathers that form a slight crest, while the back and tail are greenish-black, the chin and throat are white, and the underparts are buff-white, sometimes with a degree of brown streaking (3) (4). The beak is yellowish, with a dark upper edge, the eyes are yellow, and the legs and feet vary from yellowish to green (2) (3) (4).

The female little bittern is smaller and duller than the male, with a less glossy crown, more brownish dark markings, less contrasting buff wing patches, and brown streaks on the underparts. Juveniles are more heavily streaked than the adults and have a duller beak and legs (2) (3) (4). During the breeding season, the plumage of the adults is brighter, the feathers of the upper breast are longer, and the lower bill and bare skin of the face may flush red (3) (4). The calls of the little bittern include a deep, repeated ‘bark’, given during the breeding season (3) (4).

Five subspecies of little bittern are often recognised: Ixobrychus minutus minutus, Ixobrychus minutus payesii, Ixobrychus minutus podiceps, Ixobrychus minutus dubius and Ixobrychus minutus novaezelandiae. These vary in size and colouration; for example, some subspecies show more reddish-brown rather than buff markings. I. m. payesii, I. m. podiceps and I.m. dubius are sometimes considered separate species, although this is not generally followed (2) (3) (5). I. m. novaezelandiae has now been classified as a distinct species, the New Zealand bittern or black-backed bittern (Ixobrychus novaezelandiae), and is believed to be extinct (5).

The little bittern is a widespread species, occurring across Europe, western Asia (to northern India), Africa, Madagascar, Australia and New Guinea (2) (3) (5). I. m. minutus occurs in Europe, North Africa and Asia; I. m. payesii in Africa, south of the Sahara; I. m. podiceps in Madagascar; and I. m. dubius in southwest and eastern Australia, and sometimes in New Guinea outside of the breeding season (2) (3).

Little bitterns in Europe and Asia (subspecies I.m. minutus) migrate southwards to Africa in winter, although some may remain in the Middle East and in India. Populations elsewhere generally do not migrate, but may make local movements associated with changing water levels (2) (3). The little bittern may disperse quite widely after breeding, and is occasionally recorded outside of its normal range, for example in Iceland, northern Europe and in Britain (2) (3) (4) (5), where it has bred on rare occasions (4) (6).

Throughout its extensive range the little bittern occurs in a variety of habitats, but it is most commonly found in freshwater wetlands with dense aquatic vegetation and nearby trees and bushes, including the edge of lakes, pools and reservoirs, the wooded and marshy edges of streams and rivers, reed swamps, wet grasslands, mangroves, salt marshes and lagoons (2) (3) (4) (5). It can also be found in forests, and has been recorded at elevations of up to 1,800 metres in the Himalayas (2) (3). The little bittern may occur in more open areas of water in winter and during migration, and can be quite tolerant of human activity, sometimes occurring in rice fields, around sewage ponds, and in fields of cereals or sugar cane (2) (3) (5).

The diet of the little bittern varies with season and location, but usually comprises mostly insects, such as crickets, grasshoppers, caterpillars, beetles, and aquatic insects and larvae. The little bittern will also eat spiders, worms, crustaceans, molluscs, and small vertebrates such as fish, frogs and tadpoles, small reptiles, and birds and their eggs (2) (3) (7). This species is usually most active around dawn and dusk (2) (3) (4), but it will also feed at night, and in some areas during the middle of the day (2) (3). Individuals feed alone, stalking prey while walking slowly along the water’s edge or across vegetation, or hunting from a perch with the head and neck withdrawn (2) (3) (7). When it spots potential prey, the little bittern extends its neck and strikes with the beak (3) (7). This species has a particularly swift flight for a heron, with rapid, shallow wing beats, and it often flies with the legs dangling (3) (4).

In Europe and Asia, the little bittern breeds between May and July, while populations in Australia breed from October to January, and those in South Africa from June to February. In tropical parts of Africa, breeding usually occurs during or just after the rainy season (2) (3). Pairs generally nest alone, or sometimes in small, loose groups, usually in thick vegetation near open water, or sometimes in trees or bushes (2) (3). Early in the breeding season, the male establishes a breeding territory and advertises his presence with a barking call (3). The male also builds the nest, which is a platform of plant stems, reeds and twigs with a conical base, and is lined with finer stems and leaves (2) (3). The nest may be reused in consecutive years (3). The little bittern lays between 2 and 9 eggs (although clutch size varies with location), and the eggs are incubated by both adults, hatching after 16 to 21 days (2) (3) (7). Although the chicks may hatch a couple of days apart, late hatching chicks do not appear to lag behind earlier-hatched ones in terms of growth or survival (7). The young grow quite fast, climbing out of the nest after about a week and leaving it entirely after 14 to 16 days (3). Fledging occurs at around 27 days old, and the adults may go on to raise a second and sometimes even a third brood in the same season (2) (3).

The little bittern is not currently considered globally threatened, due to its large and widespread population (5). However, the species faces a number of threats, particularly from habitat loss and degradation, through direct destruction of habitat, pollution, or hydrological changes to rivers and wetlands (2) (5). The European population in particular underwent a decline between the 1970s and 1990s, especially in Western Europe (2) (3) (5), although in some areas it has increased (3) (5). The little bittern has also been impacted by drought and desertification on its African wintering grounds (5). This species appears to be quite localised in Australia, where it is thought to have declined, and is only known from a few locations in Madagascar (2) (3).

The little bittern (subspecies I. m. minutus) is listed on Appendix II of the Convention on Migratory Species (CMS or Bonn Convention), which aims to protect migratory species throughout their range (8), and the species is also covered by the African-Eurasian Waterbird Agreement (AEWA), which calls on parties to undertake conservation measures for birds which are dependent on wetlands for at least part of their annual cycle (9). Recommended conservation measures for the little bittern include investigating the causes of its decline in Western Europe, as well as research into the key factors which may affect its populations, such as drought, habitat alteration and the condition of its wintering grounds. Surveys are also needed to determine the status of the little bittern in Madagascar and New Guinea, and to identify the areas important to the species in these locations (3).

The conservation of the little bittern is made more complicated by its extensive range and by its various forms, which may each have its own particular conservation needs. Further research is needed into the taxonomy of this small heron, to confirm the status of the different subspecies (3).

To find out more about the little bittern, see:

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  1. IUCN Red List (December, 2010)
    http://www.iucnredlist.org/
  2. del Hoyo, J., Elliott, A. and Sargatal, J. (1992) Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, Barcelona.
  3. Kushlan, J.A. and Hancock, J.A. (2005) The Herons. Oxford University Press, Oxford.
  4. Peterson, R.T., Mountfort, G. and Hollom, P.A.D. (1993) Collins Field Guide: Birds of Britain and Europe. HarperCollins Publishers, London.
  5. BirdLife International (December, 2010)
    http://www.birdlife.org/datazone/speciesfactsheet.php?id=3756
  6. BBC - Rare little bittern breeds at Ham Wall nature reserve (December, 2010)
    http://news.bbc.co.uk/local/somerset/hi/people_and_places/nature/newsid_8854000/8854952.stm
  7. Holmes, P.R. and Hatchwell, B.J. (1991) Notes on the ecology of the little bittern Ixobrychus minutus at Haigam Rakh, Kashmir, India. Forktail, 6: 25-33.
  8. Convention on the Conservation of Migratory Species of Wild Animals (December, 2010)
    http://www.cms.int/
  9. Agreement on the Conservation of African-Eurasian Migratory Waterbirds (December, 2010)
    http://www.unep-aewa.org/