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A Crested Tern Sterna bergii colony containing 13 000-15 000 nesting pairs was located on North Bountiful Island in the Wellesley Group, Gulf of Carpentaria. This is Australia's largest known colony and may be the largest documented colony in the world. Breeding birds are thought to aggregate in autumn from foraging areas throughout the vast eastern Gulf of Carpentaria. The outer Wellesley Islands also support major colonies of Brown Boobies Sula leucogaster, Least Frigatebirds Fregnta ariel and a newly discovered colony of approximately 1000 pairs of nesting Roseate Terns Sterna dougallii. Seabird nesting follows the summer monsoonal flooding and is presumably a response to nutrient enrichment of the Gulf by river runoff.

Australia has a fairly large number of species and subspecies of birds, mostly passerines, confined to or largely dependent on mangroves, a closed forest which occurs discontinuously as a narrow chain for thousands of kilometres along tropical and subtropical coasts. About twenty-five forms are mangrove specialists compared with about eleven in New Guinea. North-western Australia is especially rich in birds specialized to mangroves and it is suggested that this region has played an important role in their evolution: isolated populations of mesic species in refuges in north-western Australia apparently became dependent on mangroves as areas of rainforest and monsoonal forest shrank during past arid periods. No such mechanism was possible in New Guinea and north-eastern Australia because large tracts of rainforest remained contiguous with mangroves throughout the Pleistocene. The area in which species and subspecies became specialized to mangroves has often become obscured by their subsequent expansion in range. Within the mangrove habitat of Australia and New Guinea, there have been one or two speciations and about twenty-five subspeciations mainly as a consequence of gaps in mangroves at the Eighty Mile Beach, western side of Joseph Bonaparte Gulf, Gulf of Carpentaria, Torres Strait and possibly the Burdekin Gap. A couple of subspeciations have resulted from gaps in range that may have been caused by competitors rather than by hysical barriers. Patchy distributions and abrupt discontinuities in mangrove birds are discussed in terms of the is!and-like distribution of their habitat. exclusion by possible competitors, geographical barriers, floristic complexity of mangroves and dispersal ability.

Gerygone fusca, G. levigaster and G. mouki are considered to compose a complex that speciated after a common ancestral form was split by severe aridity in the Pleistocene into isolated populations respectively in south-western, north-western and eastern Australia. Subsequently, fusca spread eastward along the southern part of the continent into inland eastern Australia, then northward to the Carpentarian lowlands and finally westward into the semi-deserts of central Australia, while levigaster, which had become adapted to mangroves, spread eastward to coastal eastern Australia and southern New Guinea. The allospecies fusca and levigaster are now in secondary contact without interbreeding along the southern Kimberley, head of the Gulf of Carpentaria and lower Hunter River. G. mouki, being largely confined to rainforest, has not spread from eastern Australia. The various populations of fusca have diverged behaviourally as well as morphologically: the western population tends to migrate inland and northwards in winter and is known to breed only in the south-west; the south-eastern plus central-eastern population is partly migratory and apparently breeds throughout most of its range: the Eyre Peninsula and Carpentarian populations are sedentary; and the desert population is partly nomadic. An analysis of characters in Gerygone indicates that Australian species fall into three distinct groups and that G. sulphurea and probably G. inornata-dorsalis are not particularly close to the G. fusca complex.

Principal component analyses of variation in coloration of the Little Bronze-Cuckoo Chrysococcyx malayanus minutillus and Rufous-breasted Bronze-Cuckoo C. russatus show that these forms intergrade completely and that intermediates occur throughout northern and north-eastern Queensland. Their similar ecology and behaviour combined with significant similarities in morphology, such as coloration of eye-ring of males, and songs, probably facilitate hybridization. The form C.m. barnardi of south-eastern Queensland and north-eastem New South Wales is apparently only slightly affected by russatus genes, is longer winged than minutillus. of north-western Australia from the Kimberley to the Gulf of Carpentaria and migrates north in winter to Cape York Peninsula and southern New Guinea. There is no real evidence for migration in russatus and minutillus Multi-discriminant analysis shows that minutillus-like individuals from the islands of the Banda Sea are more like C.m. rufomerus, the endemic form of the islands, than minutillus; some specimens are apparently intermediate in coloration between rufomerus and minutillus. These minutillus-like individuals appear not to be migrants from north-western Australia. Hybridization between different forms in secondary contact may be common in the C. malayanus complex; for, C.m. salvadorii of Babar Island is intermediate in coloration between C.m. rufomerus of the Banda Sea islands and the distinctive C.m. crassirostris of the Moluccas, and the long-winged population in southern New Guinea may be affected by gene-flow from the more widely distributed C.m. poecilurus of New Guinea. The pattern of variation in this complex in Australia suggests two separate invasions, the first via north-western Australia giving rise to minutillus and barnardi and the second from New Guinea producing the hybrid population on Cape York Peninsula and in north-eastern Queensland.

The shrike-thrushes C. megarhyncha and C. parvula are considered to be conspecific because they hybridize on the south-western edge of the Gulf of Carpentaria and the C. m. obscura subspecies group of northern New Guinea is a phenetic link. Geographical variation in C. megarhyncha is complex and has resulted from an interplay of ecotypy, past and present allopatric subspeciation and introgressive hybridization. In eastern Australia variation is clinal with a distinct step at the Burdekin Gap indicative of past isolation. Three or four subspecies grow may be recognized in New Guinea but far too many subspecific names are in use. The evolutionary history of C. megarhyncha is constructed from its pattern of geographical variation and the climatic regime of the late Quaternary and Holocene. Colluricincla comprises two groups of species and C. boweri is considered to be closest to the megarhyncha rather than the harmonica plus woodwardi group.

The relation between Neositta leucoptera and striata is discussed. A critical examination of the records of their occurrence in northern Queensland suggests that they are allopatric and do not interbreed. The barrier between them may lie between the Flinders and Leichhardt Rivers, and coincide with a barrier already noted between other bird species. It is proposed to call this the 'Carpentaria Barrier'. The validity of N. leucocephala is examined critically in the light of its contact with chrysoptera. It is concluded that a narrow zone of unnamed hybrids between the two occurs in north-eastern NSW and' south-eastern Queensland, that Gould's leucocephala is the correct name for white-headed birds with type locality Moreton Bay, and that lumholtzi is a synonym.

The typical form of the Brown Treecreeper Climacteris p. picumnus occurs in south-eastern Australia, a darker form with paler head markings C. p. melanota occupying the peninsula east of the Gulf of Carpentaria. Specimens from near Cardwell are intermediate, not faded, examples of melanora. Variation' occurs in C. p. picumllus, specimens from the north-east being slightly darker with slightly paler head markings. These four groups might form an interrupted cline. Alternatively, the north·eastern forms of picumnus might be regarded as intermediate. In either case it seems preferable to regard picumnus and melanota as forms of a single species.