Birds have many kinds of internal and external parasites, including viruses, bacteria and fungi, as well as protozoa, helminths and arthropods. Because parasites have negative effects on host fitness, selection favours the evolution of anti-parasite defences, many of which involve behaviour. We provide a brief review of anti-parasite behaviours in birds, divided into five major categories: (i) body maintenance, (ii) nest maintenance, (iii) avoidance of parasitized prey, (iv) migration and (v) tolerance. We evaluate the adaptive significance of the different behaviours and note cases in which additional research is particularly needed. We briefly consider the interaction of different behaviours, such as sunning and preening, and how behavioural defences may interact with other forms of defence, such as immune responses. We conclude by suggesting some general questions that need to be addressed concerning the nature of anti-parasite behaviour in birds. This article is part of the Theo Murphy meeting issue ‘Evolution of pathogen and parasite avoidance behaviours’.

The beaks of Darwin's finches and other birds are among the best known examples of adaptive evolution. Beak morphology is usually interpreted in relation to its critical role in feeding. However, the beak also plays an important role in preening, which is the first line of defence against harmful ectoparasites such as feather lice, fleas, bugs, flies, ticks and feather mites. Here, we show a feature of the beak specifically adapted for ectoparasite control. Experimental trimming of the tiny (1–2 mm) maxillary overhang of rock pigeons (Columba livia) had no effect on feeding efficiency, yet triggered a dramatic increase in feather lice and the feather damage they cause. The overhang functions by generating a shearing force against the tip of the lower mandible, which moves forward remarkably quickly during preening, at up to 31 times per second. This force damages parasite exoskeletons, significantly enhancing the efficiency of preening for parasite control. Overhangs longer than the natural mean of 1.6 mm break significantly more often than short overhangs. Hence, stabilizing selection will favour overhangs of intermediate length. The adaptive radiation of beak morphology should be re-assessed with both feeding and preening in mind.

Cospeciation occurs when interacting groups, such as hosts and parasites, speciate in tandem, generating congruent phylogenies. Cospeciation can be a neutral process in which parasites speciate merely because they are isolated on diverging host islands. Adaptive evolution may also play a role, but this has seldom been tested. We explored the adaptive basis of cospeciation by using a model system consisting of feather lice (Columbicola) and their pigeon and dove hosts (Columbiformes). We reconstructed phylogenies for both groups by using nuclear and mitochondrial DNA sequences. Both phylogenies were well resolved and well supported. Comparing these phylogenies revealed significant cospeciation and correlated evolution of host and parasite body size. The match in body size suggested that adaptive constraints limit the range of hosts lice can use. We tested this hypothesis by transferring lice among hosts of different sizes to simulate host switches. The results of these experiments showed that lice cannot establish viable populations on novel hosts that differ in size from the native host. To determine why size matters, we measured three components of louse fitness: attachment, feeding, and escape from host defense (preening). Lice could remain attached to, and feed on, hosts varying in size by an order of magnitude. However, they could not escape from preening on novel hosts that differed in size from the native host. Overall, our results suggest that host defense reinforces cospeciation in birds and feather lice by preventing lice from switching between hosts of different sizes.

The genus Brueelia Kéler, 1936a forms the core of the so-called “Brueelia-complex”, one of the largest and most heterogeneous groups of lice (Phthiraptera). Here we introduce the taxonomic history and present a revision of this group. The limits of the Brueelia-complex are discussed. We resurrect the genera Acronirmus Eichler, 1953, Corvonirmus Eichler, 1944, Guimaraesiella Eichler, 1949, Maculinirmus Złotorzycka, 1964a, Meropsiella Conci, 1941a, Olivinirmus Złotorzycka, 1964a, Osculonirmus Mey, 1982a, Rostrinirmus Złotorzycka, 1964a, Traihoriella Ansari, 1947, and Turdinirmus Eichler, 1951. We describe the following new genera: Anarchonirmus n. gen., Aporisticeras n. gen., Aratricerca n. gen., Buphagoecus n. gen., Ceratocista n. gen., Sychraella n. gen., Couala n. gen., Harpactrox n. gen., Hecatrishula n. gen., Indoceoplanetes n. gen., Manucodicola n. gen., Mirandofures n. gen., Nemuus n. gen., Priceiella n. gen., Psammonirmus n. gen., Resartor n. gen., Saepocephalum n. gen., Schizosairhynchus n. gen., Teinomordeus n. gen., Titanomessor n. gen., and Turdinirmoides n. gen.; and the following new subgenera: Camurnirmus n. subgen., Thescelovora n. subgen., Torosinirmus n. subgen., and Capnodella n. subgen. The following 37 new species are described: Anarchonirmus albovittatus n. sp. ex Pomatostomus temporalis strepitans (Mayr & Rand, 1935); Brueelia aguilarae n. sp. ex Euplectes franciscanus pusillus (Hartert, 1901); Brueelia phasmasoma n. sp. ex Coereba flaveola luteola (Cabanis, 1850); Brueelia pseudognatha n. sp. ex Pycnonotus nigricans superior Clancey, 1959; Sychraella sinsutura n. sp. ex Pomatostomus isidorei isidorei Lesson, 1827; Couala dodekopter n. sp. ex Coua cristata pyropyga Grandidier, 1867; Guimaraesiella pandolura n. sp. ex Pericrocotus flammeus semiruber Whistler & Kinnear, 1933; Harpactrox geminodus n. sp. ex Harpactes erythorcephalus erythrocephalus (Gould, 1834); Harpactrox loeiensis n. sp. ex Harpactes erythrorhynchus annamensis (Robinson & Kloss, 1919); Harpactrox pontifrons n. sp. ex Harpactes ardens ardens (Temminck, 1824); Indoceoplanetes (Capnodella) loboccupatrix n. sp. ex Lobotos oriolinus Bates, 1909; Indoceoplanetes (Capnodella) laurocorythes n. sp. ex Edolisoma holopolium holopolium (Sharpe, 1888); Maculinirmus ljosalfar n. sp. ex Oriolus chinensis diffusus Sharpe, 1877; Manucodicola acantharx n. sp. ex Manucodia ater ater (Lesson, 1830); Manucodicola semiramisae n. sp. ex Phonygammus keraudrenii purpureoviolaceus (Meyer, 1885); Meropoecus balisong n. sp. ex Merops americanus Muller, 1776; Meropoecus bartlowi n. sp. ex Merops ornatus Latham, 1802; Mirandofures altoguineae n. sp. ex Oreostruthus fuliginosus De Vis, 1898; Mirandofures kamena n. sp. ex Erythrura trichroa sigillifer (De Vis, 1897); Nemuus hoedhri n. sp. ex Artamus fuscus Vieillot, 1817; Nemuus imperator n. sp. ex Artamus maximus Meyer, 1874; Priceiella (Camurnirmus) hwameicola n. sp. ex Garrulax taewanus Swinhoe, 1859; Priceiella (Camurnirmus) paulbrowni n. sp. ex Garrulax leucolophus diardi (Lesson, 1831); Priceiella (Thescelovora) alliocephala n. sp. ex Platylophus galericulatus ardesiacus (Bonaparte, 1850); Priceiella (Torosinirmus) koka n. sp. ex Turdoides tenebrosa (Hartlaub, 1883); Psammonirmus lunatipectus n. sp. ex Serilophus lunatus lunatus (Gould, 1834); Aratricerca cirithra n. sp. ex Ptiloprora guisei guisei (De Vis, 1894); Saepocephalum stephenfryi n. sp. ex Corcorax melanoramphos (Vieillot, 1817); Schizosairhynchus erysichthoni n. sp. ex Aplonis metallica metallica (Temminck, 1824) and Aplonis metallica nitida (Grey, 1858); Schizosairhynchus minovenator n. sp. ex Mino dumontii Lesson, 1827; Sturnidoecus australafricanus n. sp. ex Corvinella melanoleuca expressa Clancey, 1961; Sturnidoecus mon n. sp. ex Euplectes hordeaceus (Linnaeus, 1758); Sturnidoecus porphyrogenitus n. sp. ex Cinnyricinclus leucogaster verreauxi (Bocage, 1870); Sturnidoecus somnodraco n. sp. ex Quelea quelea quelea (Linnaeus, 1758) and Qualea quelea lathami (Smith, 1836); Teinomordeus entelosetus n. sp. ex Eurocephalus rueppelli Bonaparte, 1853; Titanomessor sexloba n. sp. ex Laniarius erythrogaster (Cretzschmar, 1829); and Turdinirmus australissimus n. sp. ex Zoothera lunulata lunulata (Latham, 1802). The name Olivinirmus paraffinis nom. nov. is proposed as a replacement for the preoccupied Brueelia affinis Carriker, 1963. We place 23 names in synonymy, and we consider 6 species as incertae sedis, 2 names as nomina nuda, and transfer 14 species names to genera not belonging to the Brueelia-complex. We redescribe and illustrate most of the type species of the genera or subgenera included in this revision. Keys to genera, subgenera, and species groups are given, together with updated louse-host and host-louse checklists for 426 species of lice currently placed in the Brueelia-complex, including 183 new host-louse records.

Phylogenetic congruence is governed by various macroevolutionary events, including cospeciation, host switching, sorting, duplication, and failure to speciate. The relative frequency of these events may be influenced by factors that govern the distribution and abundance of the interacting groups; i.e., ecological factors. If so, it may be possible to predict the degree of phylogenetic congruence between two groups from information about their ecology. Unfortunately, adequate comparative ecological data are not available for many of the systems that have been subjected to cophylogenetic analysis. An exception is provided by chewing lice (Insecta: Phthiraptera), which parasitize birds and mammals. For a few genera of these lice, enough data have now been published to begin exploring the relationship between ecology and congruence. In general, there is a correspondence between important ecological factors and the degree of phylogenetic congruence. Careful comparison of these genera suggests that dispersal is a more fundamental barrier to host switching among related hosts than is establishment. Transfer experiments show that host-specific lice can survive and reproduce on novel hosts that are similar in size to the native host as long as the lice can disperse to these hosts. To date, studies of parasite dispersal have been mainly inferential. A better understanding of the role of dispersal will require more direct data on dispersal frequency and distances.