Meropidae

The bee-eaters are a group of non-passerine birds in the family Meropidae, containing three genera and thirty species. Most species are found in Africa and Asia, with a few in southern Europe, Australia, and New Guinea. They are characterised by richly coloured plumage, slender bodies, and usually elongated central tail feathers. All have long down-turned bills and medium to long wings, which may be pointed or round. Male and female plumages are usually similar.

As their name suggests, bee-eaters predominantly eat flying insects, especially bees and wasps, which are caught on the wing from an open perch. The insect's stinger is removed by repeatedly hitting and rubbing the insect on a hard surface. During this process, pressure is applied to the insect's body, thereby discharging most of the venom.

Most bee-eaters are gregarious. They form colonies, nesting in burrows tunnelled into vertical sandy banks, often at the side of a river or in flat ground. As they mostly live in colonies, large numbers of nest holes may be seen together. The eggs are white, with typically five to the clutch. Most species are monogamous, and both parents care for their young, sometimes with assistance from related birds in the colony.

Bee-eaters may be killed by raptors; their nests are raided by rodents, weasels, martens and snakes, and they can carry various parasites. Some species are adversely affected by human activity or habitat loss, but none meet the International Union for Conservation of Nature's vulnerability criteria, and all are therefore evaluated as "least concern". Their conspicuous appearance means that they have been mentioned by ancient writers and incorporated into mythology.

Taxonomy

The bee-eaters were first named as a scientific group by the French polymath Constantine Samuel Rafinesque-Schmaltz, who created the bird subfamily Meropia for these birds in 1815. The name, now modernised as Meropidae, is derived from ''Merops'', the Ancient Greek for "bee-eater", and the English term "bee-eater" was first recorded in 1668, referring to the European species.

The bee-eaters have been considered to be related to other families, such as the rollers, hoopoes and kingfishers, but ancestors of those families diverged from the bee-eaters at least forty million years ago, so any relationship is not close. The scarcity of fossils is unhelpful. Bee-eater fossils from the Pleistocene (2,588,000 to 11,700 years ago) have been found in Austria, and there are Holocene (from 11,700 years ago to present) specimens from Israel and Russia, but all have proved to be of the extant European bee-eater. Opinions vary as to the bee-eater's nearest relatives. In 2001, Fry considered the kingfishers to be the most likely, whereas a large study published in 2008 found that bee-eaters are sister to all other Coraciiformes (rollers, ground rollers, todies, motmots and kingfishers). A 2009 book supported Fry's contention, but then a later study in 2015 suggested that the bee-eaters are sister to the rollers. The 2008 and 2015 papers both linked the kingfishers to the New World motmots.

The bee-eaters are generally similar in appearance, although they are normally divided into three genera. ''Nyctyornis'' comprises two large species with long throat feathers, the blue-bearded bee-eater and the red-bearded bee-eater, both of which have rounded wings, a ridged culmen, feathered nostrils and a relatively sluggish lifestyle. The purple-bearded bee-eater is the sole member of ''Meropogon'', which is intermediate between ''Nyctyornis'' and the typical bee-eaters, having rounded wings and a "beard", but a smooth culmen and no nostril feathers. All the remaining species are normally retained in the single genus ''Merops''. There are close relationships within this genus, for example the red-throated bee-eater and the white-fronted bee-eater form a superspecies, but formerly suggested genera, such as ''Aerops'', ''Melittophagus'', ''Bombylonax'' and ''Dicrocercus'', have not been generally accepted for several decades since a 1969 paper united them in the current arrangement.

Species in taxonomic order

The bee-eater family contains the following species.

The Asian green bee-eater, African green bee-eater, and Arabian green bee-eater were previously considered to be a single species, and are still treated as such by some authorities.

A 2007 nuclear and mitochondrial DNA study produced a possible phylogenetic tree, although the position of the purple-bearded bee-eater seems anomalous, in that it appears amongst ''Merops'' species.

Description

The bee-eaters are morphologically a fairly uniform group. They share many features with related Coraciiformes such as the kingfishers and rollers, being large-headed (although less so than their relatives), short-necked, brightly plumaged and short-legged. Their wings may be rounded or pointed, with the wing shape closely correlated with the species' preferred foraging habitat and migratory tendencies. Shorter, rounder wings are found on species that are sedentary and make typically short foraging flights in denser forests and reed-beds. Those with more elongated wings are more migratory. All the bee-eaters are highly aerial; they take off strongly from perches, fly directly without undulations, and are able to change direction quickly, although they rarely hover.

The flight feathers of the wing comprise 10 primaries, the outermost being very small, and 13 secondaries, and there are 12 tail feathers.

The bills of bee-eaters are curved, long and end in a sharp point. The bill can bite strongly, particularly at the tip, and it is used as a pair of forceps with which to snatch insects from the air and crush smaller prey. The short legs have weak feet, and when it is moving on the ground a bee-eater's gait is barely more than a shuffle. The feet have sharp claws used for perching on vertical surfaces and also for nest excavation.

The plumage of the family is generally very bright and in most species is mainly or at least partially green, although the two carmine bee-eaters are primarily rose-coloured. Most of the ''Merops'' bee-eaters have a black bar through the eye and many have differently coloured throats and faces. The extent of the green in these species varies from almost complete in the green bee-eater to barely any green in the white-throated bee-eater. Three species, from equatorial Africa, have no green at all in their plumage, the black bee-eater, the blue-headed bee-eater and the rosy bee-eater. Many species have elongated central tail feathers.

There is little visible difference between the sexes in most of the family, although in several species the iris is red in the males and brown-red in the females, and in species with tail-streamers these may be slightly longer in males. Both the European and red-bearded bee-eaters have sex-based differences in their plumage colour, and the female rainbow bee-eater has shorter tail streamers than the male, which terminate in a club-shape that he lacks. There may be instances where bee-eaters are sexually dichromatic at the ultraviolet part of the colour spectrum, which humans cannot see. A study of blue-tailed bee-eater found that males were more colourful than females in UV light. Their overall colour was also affected by body condition, suggesting that there was a signalling component to plumage colour. Juveniles are generally similar to adults, except for the two ''Nyctyornis'' species, in which the young have mainly green plumage.

Bee-eaters have calls that are characteristic for each species. Most sound simple to the human ear, but show significant variability when studied in detail, carrying significant information for the birds.

Distribution and habitat

The bee-eaters have an Old World distribution, occurring from Europe to Australia. The centre of diversity of the family is Africa, although a number of species also occur in Asia. Single species occur in each of Europe, (the European bee-eater), Australia (the rainbow bee-eater) and Madagascar (the olive bee-eater, also found on mainland Africa). Of the three genera, ''Merops'', which has the majority of the species, occurs across the entirety of the family's distribution. ''Nyctyornis'' is restricted to Asia, ranging from India and southern China to the Indonesian islands of Sumatra and Borneo. The genus ''Meropogon'' has a single species restricted to Sulawesi in Indonesia.

Bee-eaters are fairly indiscriminate in their choice of habitat. Their requirements are simply an elevated perch from which to watch for prey and a suitable ground substrate in which to dig their breeding burrow. Because their prey is entirely caught on the wing they are not dependent on any vegetation type. A single species, the blue-headed bee-eater, is found inside closed rainforest where it forages close to the ground in poor light in the gaps between large trees. Six other species are also closely associated with rainforest, but occur in edge habitat such as along rivers, in tree-fall gaps, off trees overhanging ravines or on emergent tree crowns above the main canopy.

Species that breed in subtropical or temperate areas of Europe, Asia and Australia are all migratory. The European bee-eaters that breed in southern Europe and Asia migrate to West and southern Africa. Another population of the same species breeds in South Africa and Namibia; these birds move northwards after breeding. In Australia the rainbow bee-eater is migratory in the southern areas of its range, migrating to Indonesia and New Guinea, but occurs year-round in northern Australia. Several species of bee-eater, are intra-African migrants; the white-throated bee-eater, for example, breeds on the southern edge of the Sahara and winters further south in equatorial rainforest. The most unusual migration is that of the southern carmine bee-eater, which has a three-stage migration; after breeding in a band between Angola and Mozambique it moves south to Botswana, Namibia and South Africa before moving north to its main wintering grounds in northern Angola, Congo and Tanzania.

Behaviour

The bee-eaters are diurnal, although a few species may migrate during the night if the terrain ''en route'' is unsuitable for stopping or if they are crossing the sea. Bee-eaters are highly social, and pairs sitting or roosting together are often so close that they touch (an individual distance of zero). Many species are colonial in the breeding season and some species are also highly gregarious when not nesting.

The social structures of the red-throated bee-eater and the white-fronted bee-eaters have been described as more complex than for any other bird species. The birds exist in colonies located on nesting cliffs, and have a stable structure all year round. These colonies typically contain five to 50 burrows, occasionally up to 200, and are composed of clans of two or three pairs, their helpers, and their offspring. The helpers are male offspring from a previous year. Within the colony, the males alternate between guarding their mate and attempting to make forced copulations with other females. The females in turn attempt to lay eggs in their neighbour's nests, an example of brood parasitism. Some individuals also specialise in kleptoparasitism, stealing prey collected by other colony members. The colony's daily routine is to emerge from the nesting holes or roosting branches soon after dawn, preen and sun themselves for an hour, then disperse to feed. Feeding territories are divided by clan, with each clan defending its territory from all others of the same species, including clans of the same colony. The clans return to the colony before dusk, and engage in more social behaviour before retiring for the night. Colonies are situated several hundred metres apart and have little to do with each other, although young individuals may disperse between colonies. As such these species can be thought to have four tiers of social kinship, the individual pair, the family unit, the clan and the colony as a whole.

Bee-eaters spend around 10% of their day on comfort activities. These include sunning themselves, dust bathing and water bathing. Sunning behaviour helps warm birds in the morning, reducing the need to use energy to raise their temperature. It also has a social aspect, as multiple birds adopt the same posture. Finally, it may help stimulate parasites in the feathers, making them easier to find and remove. Due to their hole-nesting lifestyle, bee-eaters accumulate a number of external parasites such as mites and flies. Together with sunning, bouts of dust bathing (or water bathing where available), as well as rigorous preening, keep the feathers and skin in good health. Bathing with water involves making shallow dives into a water body and then returning to a perch to preen.

Diet and feeding

The bee-eaters are almost exclusively aerial hunters of insect prey. Prey is caught either on the wing or more commonly from an exposed perch from which the bee-eater watches for prey. Smaller, rounder-winged bee-eaters typically hunt from branches and twigs closer to the ground, whereas the larger species hunt from tree tops or telephone wires. One unusual technique often used by carmine bee-eaters is to ride on the backs of bustards.

Prey can be spotted from a distance; European bee-eaters are able to spot a bee away, and blue-cheeked bee-eaters have been observed flying out to catch large wasps. Prey is approached directly or from behind. Prey that lands on the ground or on plants is usually not pursued. Small prey may be eaten on the wing, but larger items are returned to the perch where they are beaten until dead and then broken up. Insects with poisonous stings are first smacked on the branch, then, with the bird's eyes closed, rubbed to discharge the venom sac and stinger. This behaviour is innate