Ninefamilies of largely arborealbirds make up theorderPiciformes/ˈpɪsɪfɔːrmiːz/, the best-known of them being thePicidae, which includes thewoodpeckers and close relatives. The Piciformes contain about 71 livinggenera with a little over 450species, of which the Picidae make up about half.
In general, the Piciformes are insectivorous, although thebarbets andtoucans mostly eat fruit and thehoneyguides are unique among birds in being able to digestbeeswax (although insects make up the bulk of their diet). Nearly all Piciformes haveparrot-likezygodactyl feet—two toes forward and two back, an arrangement that has obvious advantages for birds that spend much of their time on tree trunks[citation needed]. An exception are a fewspecies of three-toed woodpeckers. Thejacamars aside, Piciformes do not havedown feathers at any age, only true feathers. They range in size from therufous piculet at 8 centimetres in length, and weighing 7 grams, to thetoco toucan, at 63 centimetres long, and weighing 680 grams.[1] All nest in cavities and havealtricial young.
The Galbulidae and Bucconidae are often separated into a distinctGalbuliformes order. Analysis ofnuclear genes[citation needed] confirms that they form a lineage of their own, but suggests that they are better treated as asuborder. The other families form anothermonophyletic group of suborder rank, but the barbets were determined to beparaphyletic with regard to the toucans and hence, the formerly all-encompassing Capitonidae have been split up.[2] The woodpeckers and honeyguides are each other's closest relatives.[3] According to some researchers,[4] the entire order Piciformes should be included as a subgroup inCoraciiformes.
The phylogenetic relationship between the nine families that make up the order Piciformes is shown in the cladogram below.[5][6] The number of species in each family is taken from the list maintained byFrank Gill,Pamela C. Rasmussen and David Donsker on behalf of theInternational Ornithological Committee (IOC).[7]
Reconstruction of the evolutionary history of the Piciformes has been hampered by poor understanding of the evolution of the zygodactyl foot. A number of prehistoric families and genera, from the EarlyEoceneNeanis andHassiavis, theZygodactylidae/Primoscenidae,Gracilitarsidae,Sylphornithidae, and"Homalopus",[8] to theMiocene"Picus" gaudryi and thePlioceneBathoceleus are sometimes tentatively assigned to this order.[9] There are someextinct ancestral Piciformes known fromfossils which have been difficult to place but at least in part probably belong to the Pici. The modern families are known to exist since the mid-lateOligocene to early Miocene; consequently, the older forms appear to be morebasal. A large part of Piciform evolution seems to have occurred inEurope where only Picidae occur today; perhaps even some now exclusivelyNeotropical families have their origin in theOld World.
^Hackett, Shannon J.; Kimball, Rebecca T.; Reddy, Sushma; Bowie, Rauri C. K.; Braun, Edward L.; Braun, Michael J.; Chojnowski, Jena L.; Cox, W. Andrew; Han, Kin-Lan; Harshman, John; Huddleston, Christopher J.; Marks, Ben D.; Miglia, Kathleen J.; Moore, William S.; Sheldon, Frederick H.; Steadman, David W.; Witt, Christopher C.; Yuri, Tamaki (2008). "A Phylogenomic Study of Birds Reveals Their Evolutionary History".Science.320 (5884):1763–1768.Bibcode:2008Sci...320.1763H.doi:10.1126/science.1157704.PMID18583609.S2CID6472805.
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