Burhinus


Burhinus is a genus of birds in the family Burhinidae. This family also contains the genus Esacus. The genus name Burhinus comes from the Greek bous, ox, and rhis, nose.
The Burhinus are commonly called thick-knee, stone-curlew or dikkop. They are medium-sized, terrestrial waders, though they are generally found in semi-arid to arid, open areas. Only some species of Burhinus are associated with water. The genus ranges from 32 cm to 59 cm in size. Burhinus are characterised by their long legs, long wings and cryptic plumage. Most species have a short, thick, strong bill, to which the generic name alludes. The stone-curlews are found all over the world except Antarctica. They are mainly tropical, with the greatest diversity in the Old World.

Taxonomy and systematics

The genus Burhinus was erected by the German zoologist Johann Karl Wilhelm Illiger in 1811 with the bush stone-curlew as the type species. The name combines the Ancient Greek bous meaning "ox" and rhis, rhinos meaning "nose".
Determining the correct placement of this family can be difficult as they are very ancient species. Burhinus are best placed in Charadriiformes. They resemble bustards and have been previously classified with them in Gruiformes. Their placement in Gruiformes is considered convergent evolution, as both orders have the same lifestyle and biotopes. Comparisons made of skeleton, biochemistry and parasites plus down on young, confirm Burhinus as a charadriiform.
Based on multi-locus analysis, the stone-curlew family is probably closest to the family Charadriidae, not Scolopacidae. The optimal maximum likelihood phylogenetic reconstruction using multi-locus analysis placed Burhinus within Charadrii, sister to Scolopaci. They have some similarities to Glareolidae and some phylogenies do place them as a sister clade to this family. however this is also considered convergent evolution. DNA–DNA hybridisation as well as RAG-1 and myoglobin intron-II sequence data supports a link to Recurvirostridae. Burhinus and Chionis together are sister to the rest of the Charadriidae.
A phenotypic study of Charadriiformes suggests that Burhinidae should consist of three genera – Esacus, Burhinus plus resurrected Orthorhampus. In this model, the bush stone-curlew would be removed from Burhinus and placed in a subfamily Esacinae with Esacus. This subfamily would be known as the greater thick-knees, while the remainder of the genus Burhinus would fall into Burhininae, the lesser thick-knees. This is based on character analyses of skeletons, skin and natal patterns. Esacus has sometimes been lumped within Burhinus, but Esacus are generally larger and chunkier with a larger bill and less mottled plumage. Burhinus is clearly distinct from Esacus, except for the bush stone-curlew, which is the same size as Esacus. However, the bush stone-curlew has more similar plumage to the rest of Burhinus. The Indian stone-curlew was split from the Eurasian species, as it does not migrate. It is possible that the population of Eurasian stone-curlews on the Canary Islands should also be split in this way as this population shows very little genetic variation.
The bush stone-curlew has had a confusing history of classification. This species has previously been considered two species and B. magnirostris has at times been used for this species, with the same specific epithet now used for the beach stone-curlew in the sister genus Esacus, leading to much confusion. The Bush stone-curlew is now B. grallarius, as described by John Gould in 1845.

Species

There are eight species of Burhinus. No species is threatened and none have become extinct since 1600.
PictureNameBinomial nameDistribution
Eurasian stone-curlewBurhinus oedicnemusEurope, north Africa and southwestern Asia.
Indian stone-curlewBurhinus indicusSouth and South-eastern Asia
100pxSenegal thick-kneeBurhinus senegalensisAfrica between the Sahara and the equator
100pxWater thick-kneeBurhinus vermiculatusAngola, Botswana, Burkina Faso, Burundi, Cameroon, Central African Republic, Republic of the Congo, Democratic Republic of the Congo, Ivory Coast, Eswatini, Ethiopia, Gabon, Ghana, Kenya, Liberia, Malawi, Mozambique, Namibia, Niger, Nigeria, Rwanda, Senegal, Somalia, South Africa, Tanzania, Uganda, Zambia, and Zimbabwe.
100pxSpotted thick-kneeBurhinus capensiscentral and southern Africa.
100pxDouble-striped thick-kneeBurhinus bistriatusHispaniola, as well as Central and South America from southern Mexico south to Colombia, Venezuela and northern Brazil.
Peruvian thick-kneeBurhinus superciliarisChile, Ecuador, and Peru.
100pxBush stone-curlewBurhinus grallarius Australia.

There are three fossil species known:
  • Burhinus lucorum Bickart, 1981 from the Early Miocene of Nebraska
  • Burhinus aquilonaris Feduccia, 1980 from the Pleistocene of Kansas
  • Dwarf thick-knee, Burhinus nanus Brodkorb, 1959 from the Late Pleistocene of The Bahamas

    Description

Burhinus are a genus of long-legged, large-eyed, terrestrial waders with eerie nocturnal calls. They range from 32 cm to 59 cm. There are generally only minor plumage differences between the sexes, and the late juveniles of Burhinus appear similar to the adults. Females may be smaller. All species of this genus have cryptic plumage of sandy browns with streaks and mottles, usually with spots of cream, buff, brown and black. The head of the Burhinus has a broad domed crown, giving rise to the Afrikaans name of dikkop, which translates to "thick head". The closed wings of most Burhinus have banded upper coverts. This is not as prominent on the American species and the Peruvian thick-knee is plainer and greyer except for the head. In flight, Burhinus’ wing plumage is much more striking with patterning that contrasts with the otherwise cryptic plumage. All Burhinus have black primary feathers with white patches, which is most developed in Bush stone-curlews. The wings are long and are held straight and out stretched in flight. Burhinus have a marked carpal angle and the outer wing has minimal tapering, with a pointed tip in some species. The inner wing is thinner, with 16-20 secondary feathers. Burhinus have 11 primary feathers, of which the outer most is very small and covered by the primary coverts. The twelve tail feather are generally short and rounded, except in the Spotted thick-knee which is medium in length and the Bush stone-curlew which has a longer more tapered tail. Their legs often extend beyond the tail in flight.
Typically, the Burhinus bill is stout, and is considered medium to short in length for a wader. The tip of the bill is bulbous with sharp point when viewed from side, while from the top view it has a broad base. The bill is mostly dark but can have yellow at the base, with slit-like perforated nostrils like Laridae.
The long legs of Burhinus range from pale ochre to vivid yellow in colour. The tibia is exposed and the swollen tibiotarsal is where name ’thick-knee’ came from. Their legs are markedly scaled and only have three slight webbed, forward facing toes with no hind toe. Burhinus move on the land with a measured sedate walk; head and body held horizontal in the same position to when they lay on the ground. The long strides easily move from walk to run with head held forward. Flight can quickly follow and their flight is fast and direct with little maneuverability. Burhinus will generally run before they take off and run for a short distance on landing. Their active flight consists of regular, shallow wing beats similar to Numenitus.
All Burhinus have a complete post-breeding moult which can take 4–5 months. The primaries are lost in descending sequence. The Eurasian and Senegal thick-knees may suspend moulting of primaries in winter and finish in spring, leading to an overlap of moulting and breeding. It is very unusual for breeding and moulting to overlap, and the slow moult may possibly be to maximise re-nesting potential. Burhinus’ secondary feathers are usually not replaced in one season, with the inner and outer feather being shed first. A pre-breeding moult may just be the head and neck and sometimes not at all. Once they have fledged, juvenile Burhinus will moult only their head and body, some wing-coverts and central tail. Juveniles will moult their secondary wing feathers after their first winter. This can be helpful when estimating the age of young birds.

Distribution and habitat

More species of Burhinus species are found in the tropics and sub-tropics, than other bioregions. They are generally sedentary and can live their whole lives within a few kilometres of hatching site. Eurasian stone-curlews are the exception, breeding in temperate areas and migrating south to avoid the northern winter. Birds from Britain and France will migrate to Italy, Greece, and Turkey and further. Bush stone-curlews will move to find food. Both Eurasian and Bush stone-curlews use a much larger area outside the breeding season. Double-striped, Peruvian and the spotted thick-knees are rarely seen outside breeding areas while Senegal thick-knees will move based on rains in north. Burhinus are very typical in their requirements and are usually found in dry open country though the Senegal and water thick-knees are associated with water. They can breed in arid and semi-arid habitats but not in closed woodland or forest. They are generally found in open spaces with extensive visibility on dry fairly even ground. Their habitat is usually a mixture of bare earth and vegetation with some species, like the Bush stone-curlew, found in lightly timbered, open forest and woodland. Eurasian stone-curlews are mostly found on free draining sandy soils with stones, both semi-natural and tilled. They will roost in the shade at the edge of a forest. Partly cleared farmland can be used as well but intense cultivation will drive them away. Burhinus are generally timid and wary, though in some case they may live close to humans using resources from dung and crops, as well as nesting on rooftops.