Hornbills, hoopoes and woodhoopoes are all similar in appearance and have been classified together in a group termed Bucerotes. Vague similarities with other long-billed, forest-dwelling birds (like woodpeckers, long-billed cuckoos and such passerines as tree-creepers) meant that early ornithologists were often confused about the affinities of these birds. By the late 1800s, however, most had realised that all three were close relatives, and that they were most likely close kin of kingfishers, bee-eaters and rollers. The group that includes kingfishers, bee-eaters, rollers, hornbills and hoopoes has been termed Coraciiformes; some recent phylogenies have found Coraciiformes of tradition to be paraphyletic to Piciformes (woodpeckers and kin) (e.g., Mayr et al. 2003, Cracraft et al. 2004, Ericson et al. 2006, Hackett et al. 2008). The resulting ‘coraciiform’ + piciform clade appears robust and has recently been named Picocoraciae (Mayr 2010).
Within Picocoraciae, a close link between hornbills, hoopoes and woodhoopoes is firmly established on the basis of anatomical and genetic evidence. All three groups share a list of features not seen in other birds, and have similar skulls, chest bones and leg bones.
Hoopoes and woodhoopoes are similar, slender-billed birds of Old World woodlands, forests and grasslands [adjacent image shows Green woodhoopoe Phoeniculus purpureus (also called the Purple or Red-billed woodhoopoe): photo by Axel B√ľhrmann, from wikipedia]. The Hoopoe Upupa epops [shown at top; photo by J. M. Garg, from wikipedia] is widespread, occurring across Europe, Africa including Madagascar, and Asia. These populations differ somewhat in size and colour and about ten subspecies have been named: some experts think that a second species (U. africana) should be recognised for African hoopoe populations. A large, flightless species (U. antaios) previously inhabited St Helena in the South Atlantic (Olson 1975).
Hoopoes are unmistakeable, combing a long, decurved bill with an erectile crest, pinkish or buff-coloured head and body plumage, and black-and-white striping on the wings and tail. They probe into bark, soil and leaf litter with the long bill, and feed mostly on insects and their larvae. Much of their foraging is done on the ground. Hoopoes are more flexible in terms of nesting behaviour than hornbills and woodhoopoes, and will use burrows, nest boxes and buildings as nest sites. The nest site soon becomes fouled with droppings and food fragments.
Woodhoopoes – some species of which are sometimes called scimitarbills – are restricted to Africa, though they also inhabited Europe during the Miocene (Ballman 1969). Between eight and ten species are known (ideas differ on which populations should be regarded as species: see Simmons et al. (2005) and Cunningham & Cherry (2005)). Most forage in the trees of woodland and grassland environments, but two are restricted to rainforests. Woodhoopoes are hoopoe-shaped, but differ from them in being crestless and in possessing dark, metallic plumage. Some have straight bills, while in others the bill is strongly curved. Several species have white patches on their wings and tails, and the White-headed woodhoopoe Phoeniculus bollei [shown here, painting by J. G. Keulemans] is particularly distinctive.
Woodhoopoes are more agile than hoopoes, and are experts at climbing up tree trunks and clambering about among branches. They even hang upside down on occasion, and often use their tail feathers as props in similar fashion to woodpeckers. When on the ground, woodhoopoes hop, whereas hoopoes walk.
One interesting detail of woodhoopoe biology is that the sexes often differ in bill length, with males having substantially longer, more curved bills (a male’s bill can be more than one-third longer than a female’s) [adjacent photo - showing bill dimorphism in Green woodhoopoe - from Andrew Radford's site]. Females forage on branches for small insects, while males probe into crevices for larger prey (Jamieson & Spencer 1996, Radford & du Plessis 2003). Sexual dimorphism in bill length and shape is fairly widespread in birds, and it means that the sexes avoid competing with one another by acting as separate ‘ecological species’ (see the article Sexual dimorphism in bird bills: commoner than we’d thought).
Like hornbills and hoopoes, woodhoopoes are cavity nesters. However, Green woodhoopoes at least cannot use cavities that are open to the elements and require cavities partially covered by bark or vegetation. These partially covered cavities are rare commodities, and are often taken over by bees, rodents and other animals. It also seems that woodhoopoes are sensitive to cool night-time temperatures and ordinarily cluster together under cover to stay warm at night. All of this means that they’re constrained in terms of where they can live and breed (du Plessis 1992). [Image below shows Common scimitarbill Rhinopomastus cyanomelas by Steve Garvie, from wikipedia.]
Because woodhoopoes often choose roost or nest sites in weak, partially rotten wood, they are poorly protected from mammalian predators. Genets and cats take a heavy toll on woodhoopoe populations, and woodhoopoe mortality seems to be about twice as high as that of other small birds from the same habitats. Woodhoopoes are not completely defenceless though: female hoopoes and woodhoopoes can both produce a dark, foul-smelling oil when threatened on the nest, and can even spray it from their oil gland (located beneath the tail).
Woodhoopoe family life
Some woodhoopoe species are highly social birds that live in groups with a well-established dominance hierarchy. The Green woodhoopoe is a co-operative breeder, and as many as ten birds will work together with a mated pair to help raise their chicks (du Plessis 1991, du Plessis et al. 2007). As is typical among co-operative breeders, these helpers are often close relatives of the pair, typically being offspring from previous clutches. However, unrelated birds of the same sex may also form social groups, with the non-breeders being subordinate to the breeding, territory-holding birds. It seems that this behaviour is reciprocal, and that the roles are exchanged when the helpers become territory-holders themselves. The breeding behaviour of other woodhoopoe species is poorly known, so it is possible that co-operative breeding occurs in some of them as well.
All individuals of the social group help defend the breeding territory, but the subordinate birds actually seem to contribute more to territory defence than the breeding pair. Groups use ‘vocal rallying’ (or choruses) to advertise their occupation of a territory, and call for longer when they perceive that a neighbouring group consists of many individuals (Radford 2003). Males undergo a change in voice at sexual dimorphism (Radford 2004) and, because the composition of a group means that it has a distinct rallying sound compared to others, groups can identify other groups with ease. A group answers faster to an unfamiliar group, or to a trespassing familiar group, than to a familiar group in its expected location (Radford 2005).
And, just to remind you what this all would have looked like had the book worked out, here’s the layout we planned…
For previous articles on members of Picocoraciae, see…
- She was a very strange woodpecker
- Woodpeckers: barbed tentacles and the avoidance of brain injury
- A case of dead kingfishers
- The other ground hornbill
- Ground hornbills: savannah-dwelling, avian pseudo-hominids
Refs – –
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