CHAPTER 2
Avian biogeography
Why study biogeography of birds ?
Different aspects of avian biology addressed
• how have new bird species arisen ?
• how did they come to be distributed in the way they are ?
• how are patterns of distribution and diversity maintained ?
• how does their (behavioural) ecology differ between regions ?
Why study biogeography of birds ?
Birds as ecological model
• evolutionary relationships well understood
Why study biogeography of birds ?
Birds as ecological model
Why study biogeography of birds ?
Birds as ecological model
Irwin et al. 2001. Speciation in a ring. Nature 409: 333-337
Why study biogeography of birds ?
Birds as ecological model
• evolutionary relationships well understood
• geographical pattern of morphological variation well studied
• distributional patterns well mapped
Why study biogeography of birds ?
Birds as ecological model
Opisthocomus hoazin
Why study biogeography of birds ?
Birds as ecological model
• evolutionary relationships well understood
• geographical pattern of morphological variation well studied
• distributional patterns well mapped
• high mobility allows presence and radiation on remote islands
• very strong seasonal migration
• large-scale ringing data
Continental birds
Continental birds
• level of distinctiveness of land-masses reflects both their relative
position and geological history (tectonics, duration and degree of
isolation, opportunities for separate evolution)
Continental birds
Archaeopteryx – ca 150
Geological time scale and break-up of Gondwanaland
Continental birds
• level of distinctiveness of land-masses reflects both their relative
position and geological history (tectonics, duration and degree of
isolation, opportunities for separate evolution)
• combination of present distribution patterns along with palaeogeological evidence
• 19th century: global system first developed for passerine birds,
then modified by Alfred Russel Wallace (1876) to apply to animals
in general
• crucial barriers are seas, deserts, mountain ranges, climaticvegetation ecotones
Continental birds
Main biogeographical regions of the world
Continental birds
Main biogeographical regions of the world
Continental birds
Main biomes (vegetation zones) of the world
Continental birds
• proportions of families, genera and species shared depend on the
effectiveness of the barriers and the distances between the
regions, both now and in the geological past
• the longer an area has been isolated, the higher the taxonomic
rank of its endemics
Continental birds
Palaearctic region
Continental birds
Palaearctic region
• 46 mil km²; more than twice as big as any other region
• within each type of habitat, more species at E than W end of
Eurasian land-mass, due to the greater severity of the glaciations
in the west
Continental birds
Palaearctic region
• 46 mil km²; more than twice as big as any other region
• within each type of habitat, more species at E than W end of
Eurasian land-mass, due to the greater severity of the glaciations
in the west
• marked seasonality
Continental birds
Palaearctic region
• Atlantic has proved an effective barrier to range extension in
landbirds: Northern wheatear, Cattle egret, Little gull, Fieldfare,
Spotted sandpiper, Wilson’s phalarope
Continental birds
Palaearctic region
• Bering Strait: dry land during glacial periods (10.000 y ago) and
holds series of islands (stepping stones): Yellow wagtail, Northern
wheatear, Arctic warbler, Snow goose, Grey-cheeked thrush,
Yellow-rumped warbler (tundra or boreal forest)
Continental birds
Palaearctic region
• Mediterranean Sea ca 5 mil y (early Pliocene); less effective
barrier with many islands: North African species are Palaearctic in
affinity (e.g. 165 species breeding but not extending in subSaharan Africa): Dupont’s lark, Moussier’s redstart, Tristram’s
warbler, Algerian nuthatch supplemented by Sub-Saharan species
(White-rumped swift, Black-crowned tchagra)
Continental birds
Palaearctic region
• birds of N and C Sahara predominantly Palaearctic, mainly at
oases (Cirl bunting, Eurasian spoonbill, Little owl) supplemented by
Afrotropical species extending N (Small buttonquail, Red-knobbed
coot, Little green bee-eater, Senegal thick-knee, Nile valley
sunbird)
Continental birds
Palaearctic region
• mountainous southwest Arabia usually included in Afrotropical
Region, while birds of Persian Gulf and Iran predominantly
Palearctic
Continental birds
Palaearctic region
• mountainous southwest Arabia usually included in Afrotropical
Region, while birds of Persian Gulf and Iran predominantly
Palearctic
• at least 937 landbird species breed regularly in the Palearctic
Region, which is a low number and a low level of endemism (no
endemic families, 9% genera and 47% species restricted to the
region)
Continental birds
Palaearctic region
• localised endemics at Madeira, Canary Islands, Cyprus, Azores,
Corsica and Caucasus
Continental birds
Palaearctic region
Continental birds
Palaearctic region
• within both regions, proportion of shared species increase N,
resulting in a Holarctic distribution: e.g. Red crossbill, Northern
goshawk, Common goldeneye (boreal forest); Rock ptarmigan, Gyr
falcon, Lapland longspur (tundra); King eider, Sabine’s gull,
Glaucous gull (arctic ocean)
Continental birds
Palaearctic region
• closely related species point towards recent divergence in
geological time (ancestral homes differ between pairs); e.g 0.5 mil
y for Northern harriers; 4.3 mil y for Eagle owls; 7.9 mil y for
Pygmy owls
Continental birds
Ecologically equivalent and closely related
species in Eurasia and North America
Continental birds
Palaearctic region
• some families poorly represented, such as 7 and 2 species of
Kingfishers (86 species) and 1 and 2 species of Parrots (360
species)
• examples of poorly represented Old World families in North
America are Warblers, Shrikes and Larks, and the representatives
are often more closely related to eastern Asian species
• examples of poorly represented New World families in Eurasia are
Wood warblers; Tyrant flycatchers and Vireos
Continental birds
Palaearctic region
• migrant passerines in both regions are phylogenetically more
different from each other than the residents and short-distance
migrants
• suggests that many long-distance passerine migrants (mainly
insectivorous warblers and flycatchers) derived from essentially
tropical families
• not true for shorebirds and waterfowl
Continental birds
Indomalayan (Oriental) region
Continental birds
Indomalayan (Oriental) region
• 9.6 mil km²; mainly within the tropics; northern border
(Himalayas) corresponds with climate-vegetation ecotone
• includes Indonesian archipelago, Philippines, Borneo, Sulawesi,
Sumatra, Java and Bali
• transition zone between Oriental and Australian Regions called
Wallacea; 120 m lower sea level during glaciations, when Sunda
shelf was connected to continental Asia; deep water channel east
of Sunda shelf contains oceanic islands such as Moluccas and
Lesser Sundas
Continental birds
Boundary between Indomalayan and
Australasian faunas
Continental birds
Indomalayan (Oriental) region
• not known till when Philippine Islands were attached to SE Asia,
Sulawesi may never have been connected to mainland Asia; more
avian affinities with Philippines and Lesser Sunda Islands than with
Sumatra and Borneo
• 3rd richest Region with 1697 species; 3 endemic families
(Leafbirds, Asian frogmouths and Bearded bee-eaters), 129
endemic genera, 1184 endemic species (70%)
Continental birds
Indomalayan (Oriental) region
Continental birds
Indomalayan (Oriental) region
• major wintering area for east Palaearctic breeding birds
• shares most families (but not species) with Africa, probably
because of connection by broad stretch of tropical habitats through
Middle East till Miocene (often considered single Palaeotropical
Region for plants)
Continental birds
Indomalayan (Oriental) region
• at family level both regions share Broadbills, Bulbuls, Sunbirds,
Weavers, Honeyguides
• family Phasianidae particularly well represented, and centre of
radiation for Pittas, Laughing thrushes, Drongos, Flowerpeckers
Continental birds
Indomalayan (Oriental) region
Continental birds
Indomalayan (Oriental) region
• richness partly results from fusion of 3 separate faunas
originating at different land-masses, and infiltration from at least 2
others; some regions isolated for long periods; inclusion of many
islands (e.g. Philippines 7100 islands) with high endemism
(Philippines: 43% of 403 breeding species endemic; Sulawesi 36%
of 247 species)
• strong difference between SE part of Eurasia and rest of landmass due to effectiveness of Himalayan chain and Tibetan plateau,
abundance of islands, and tropical forest belt
Continental birds
Afrotropical (Ethiopian) region
Continental birds
Afrotropical (Ethiopian) region
• mainly tropical region; south of the Sahara and Madagascar,
Comoro, Seychelles and Mascarene Islands (islands sometimes
separated as a distinct Malagasy Region)
• northern border poorly defined across Arabia
• ca 21 mil km² (1.25 mil south of tropics)
Continental birds
Afrotropical (Ethiopian) region
• main vegetation types run in latitudinal belts, becoming more
arid and open north- and southwards from the equator, but basic
pattern is complicated by topography
• markedly seasonal climate with distinct dry and wet seasons
Continental birds
Afrotropical (Ethiopian) region
• although similar in latitude as Neotropical Region, it contains less
than half as many landbird species (ca 1950 regional breeders),
partly because tropical and montane forest cover much smaller
areas and high arid plateaus are more extensive
Continental birds
Afrotropical (Ethiopian) region
• among passerines, Weavers, Waxbills, Starlings, Larks, Shrikes
and Sunbirds are especially well represented. Also rich in
Francolins, Bustards, Barbets, Honeyguides and Cisticola’s, but
poor in Parrots and Woodpeckers.
Continental birds
Afrotropical (Ethiopian) region
• both species of Oxpecker have evolved in close association with
large herbivorous mammals
Continental birds
Afrotropical (Ethiopian) region
• 11 endemic families of mainland Africa and 6 of Malagasy mostly
contain small numbers of species, and some are represented
among fossils from Europe and North Africa
Continental birds
Afrotropical (Ethiopian) region
• main centres of endemism: Ethiopian massive, Cameroon
Mountains, East African Mountains, Somali and Namibian arid
zones, Gulf of Guinea Islands (Principé, São Tomé)
Continental birds
Afrotropical (Ethiopian) region
• hard to decide in which direction colonization took place, but
some seem certain: e.g. two African Pittas, four African Broadbills,
eight African Drongos (from SE Asia); three African Wagtails,
Longbilled pipit (from Eurasia); Cisticola juncidis, Ploceus weavers,
Estrildinae (to SE Asia)
• enormous influx from Palaearctic migrants (about a third of all
species from that region), some species occasionally breed in
Africa
Continental birds
Afrotropical (Ethiopian) region
• Malagasy subregion: Madagascar fourth largest island on earth,
ca 400 km from Africa; thought to have broken away from
Gondwanaland as a unit with India > 100 mil y ago, then
separated from India 80-85 mil y ago.
Continental birds
Afrotropical (Ethiopian) region
• some species such as the extinct Elephantbirds may date back to
this period; other species may have arrived later by cross-water
flights
Continental birds
Afrotropical (Ethiopian) region
• various levels of endemism (from families to subspecies) attest to
the continuation of the colonization process over long period of
time.
• Some part of the avifauna is relictual, e.g. fossil birds similar to
Madagascan ground-rollers from North-America
Continental birds
Afrotropical (Ethiopian) region
• Avifauna of Madagascar relatively poor (198 breeding landbird
species), but about 25% of the genera and >50% of species
endemic.
• Small average number of species per genus implies low rate of
recent speciation (or immigration) or high rate of recent extinction
(low speciation:extinction ratio). One adaptive radiation has given
rise to diverse range of songbird species, resembling bulbuls,
babblers and warblers; another has given rise to 14 species of
Vanga shrikes (classified in 12 different genera)
• Mascarenes, Seychelles and Comoros derived birds mainly from
Madagascar (sharing 22 landbirds); many flightless species went
extinct (e.g. Dodo)
Continental birds
Australasian region
Continental birds
Australasian region
• comprises eastern Indonesian Islands, New Guinea, Australia,
New Zealand and neighbouring Pacific Islands;
Continental birds
Australasian region
• total area ca 0.9 mil km²; large proportion semi-arid or arid;
40% in the tropics; Australia is the dries continent; bird
movements are mainly constrained by expanses of desert rather
than by mountain ranges
Continental birds
Australasian region
• Australia has been physically isolated for more than 55 mil years,
giving rise to a unique fauna derived from Gondwanan heritage;
repeatedly connected to New Guinea and Tasmania, most recently
10.000 years ago; relatively little migration to and from other
regions
• lack of glaciations and frequent fires have provided nutrient-poor
conditions and some of the least productive seas on earth
Continental birds
Australasian region
• annual variations in rainfall greater than within-year seasonal
variations (El Niño – Southern Oscillation); ca 1/3 of all bird
species nomadic, and large proportion nest in tree hollows (ca 11%
are obligate cavity nesters; about twice as many as on any other
continent)
• 1592 landbird species; 2nd richest in landbird species per unit
area; high speciation due to fragmented nature of forests and
many islands; 25% of families, 61% of genera and 89% of species
endemic; 2nd highest degree of endemism (after Neotropics)
• avifaunal differences between Guinea, Australia and Tasmania are
mainly related to habitat difference
Continental birds
Australasian region
• parrots, pigeons and doves, kingfishers and honeyeaters very
well represented (latter most diverse group in Australia and New
Guinea)
Continental birds
Australasian region
• curious birds are Birds-of-Paradise, Bowerbirds, Megapodes,
Kiwis, etc.
Continental birds
Australasian region
• based on fossils, major components inherited directly from
Gondwanaland (earliest know passerine early Eocene, ca 55 mil y
ago); autochthonous component also includes Ratites, Penguins
and possibly Lyrebirds, Pigeons, Parrots, Kingfishers
• relatives (same families) in Africa and South America reflect a
common origin; some families currently restricted to region are
represented among Eocene/Oligocene fossils from Eurasia (Owletnightjars, Frogmouths, etc)
Continental birds
Australasian region
• DNA-DNA hybridization indicates that passerines mainly result
from endemic radiation within Australia rather than from
successive colonization from Eurasia; majority fall into 3 distinct
assemblages with convergence in form and habit towards unrelated
birds in northern hemisphere
Continental birds
Australasian region
Relationships and divergence of Australian passerines
Continental birds
Australasian region
• 2nd major component from Palearctic-Oriental regions where
close relatives are now found, followed by secondary radiations
(e.g. Waterbirds, Raptors, Swifts, Pittas, Swallows, Thrushes,
Silver-eyes); show varying degrees of differentiation (including
distinct genera)
Continental birds
Australasian region
Decline in species numbers and diversity between
Afrotropical-Indomalayan regions and Australasia
Continental birds
Australasian region
• very few characteristic Australian genera breached Wallace’s line
to reach the oriental Region, and none reached Africa; unequal
exchange between continents may reflect competitive superiority
of members of one avifauna
Continental birds
Australasian region
Continental birds
Australasian region
• New Guinea is tropical, mountainous and wet, close to the
Oriental Region and has rich avifauna (i.e. more species than
Australia); centre of distribution of Birds-of-Paradise, Bowerbirds,
Cassowaries, Megapodes and Crowned pigeons
• New Caledonia separated from Gondwana about the same time
as New Zealand, and has a poor avifauna (71 species), including
the flightless Kagu (separate family), 4 other endemic genera and
14 endemic species
Continental birds
Australasian region
• avifauna of New Zealand has 3 components: ancient group,
Australian colonists, and Holarctic colonists
• new Zealand wrens and extinct Moa preceded split with Australia;
other ancient species (without close relatives elsewhere) comprise
Wattlebirds (e.g. Saddleback), Kokato and the extinct Huia and
New Zealand thrushes
• insular influences are seen in flightlessness, lack of sexual
dimorphism, and melanistic forms (common cause: lack of
selection pressure in absence of mammalian predators)
• 2nd component (Australian origin) includes Dollarbirds, Parrots,…
Continental birds
Australasian region
• in recent times, habitat shifts due to anthropogenic activity
increased chances of vagrant establishment (at least 8 Australian
species during last 150 y)
• 3rd component (Holarctic origin) includes species such as South
Island (Pied) Oystercatcher and New Zealand Scaup
Continental birds
Australasian region
Continental birds
Australasian region
• like Madagascar, New Zealand has very low species-per-genus
ratio suggesting recent extinctions and little recent speciation
• mt DNA in museum specimens suggest major genetic bottleneck
ca 28 mil y ago (Oligocene) and radiation from one/few
mitochondrial lineages within each group
• New Zealand experienced very different history from rest of
Australia (colder, frequent glaciations and volcanic activity,
resulting in more fertile soils)
Continental birds
Nearctic region
Continental birds
Nearctic region
• North America N of the tropics and Greenland; S border usually
placed through Mexico, along N edge of the tropical rain forest
(climate-vegetation boundary)
• covers ca 21 mil km² landmass and 2 mil km² ice (Greenland)
• in contrast to Europe, major topographical features extend
longitudinally; hence areas E/W of Rockies have large numbers of
exclusive species despite similar habitats; smaller areas of
endemicity on mountain/lowland areas
Continental birds
Nearctic region
Continental birds
Nearctic region
• also latitudinal change in avifauna, with climatic and vegetation
belts increasingly better defined northwards
• 732 regular breeding species, less than in any other region; no
endemic bird families, but 19% genera and 54% species endemic
Continental birds
Nearctic region
• North American continent connected with Europe (via Greenland)
in early tertiary and intermittent connections with Asia across
Bering Strait bridge (only 10.000 y ago); connection with South
America occurred ca 3.5 mil y ago (Pliocene)
• as Central America is well vegetated, much less separation of
Nearctic-Neotropical avifaunas than of Palaearctic-Afrotropical
• S half of North America was humid and tropical as far N as San
Francisco/Washington DC during 1st half of Tertiary, permitting
evolution of tropical North American fauna (distinct of South
America); intermingled when Panamanian land-bridge established
Continental birds
Nearctic region
• avifauna consists of 4 elements: (i) old indigenous (Wrens,
Dippers, Gnatcatchers, Silky flycatchers, American sparrows,
Motmots), (ii) young Holarctic (trans-atlantic connection with
Europe but origin uncertain: Cranes, Grouses, Thrushes; (iii)
recent immigration from Asia (Horned lark, Brown creeper, Pipits,
Nuthatches, Corvids, Tits, Kinglets, Barn Owl, Hirundines); (iv)
immigrants from South America with major radiation in North
America (Tyrannid flycatchers)
Continental birds
Nearctic region
Continental birds
Nearctic region
• Greenland mostly considered part of Nearctic Region; among 59
regular breeders, 38 circumpolar, 8 from Europe, 13 from Eurasia
• as almost whole of Greenland was ice-covered until 6.000 years
ago, much of its avifauna results from recent immigration; yet, its
Redpolls are considered subspecifically endemic
Continental birds
Neotropical region
Continental birds
Neotropical region
• includes Central and South America, West Indies and other
islands near South America (incl. Galapagos and Falklands); ca
18.2 mil km²
• mainly covers tropical forest, but also desert, grassland (pampas)
and temperate/montane habitat
Continental birds
Neotropical region
Continental birds
Neotropical region
• a few tropical species (Trogon, Chachalaca) extend into North
America, while some Nearctic species such (e.g. Turkeys) extend
into South America
• Central America contains mix of old indigenous species and
recent invadors from South America (Tinamous, Jacamars,
Puffbirds, Toucans, Ovenbirds, Antbirds, Manakins, Cotingas)
• northward spread of open-country species due to destruction of
former forest barriers
Continental birds
Neotropical region
Continental birds
Neotropical region
• contains longest mountain range (Andes) with central high desert
(Altiplano) holding largest expanse of salt; Amazon (> 5000 km)
drains 40% of continent and acts as significant dispersal barrier;
largest seasonal swamp (Pantanal, > 60.000 km²), true desert
(Atacama)
• richest in breeding bird diversity (3370 breeding species, 2
endemic orders, 20 endemic families, 686 endemic genera, 3121
endemic species); shares 7% species but 65% families with
nearctic Region
• highest level of endemism reflects ancient and distinctive
evolutionary history
• many migrant species from North America, mainly wintering in
forest
Continental birds
Neotropical region
• South America was isolated as a giant island continent for more
than 30 million years
Continental birds
Neotropical region
• characteristic families (Guans, Ovenbirds, Woodcreepers, Ground
antbirds, Tyrant flycatchers, Cotingas, Manakins, Puffbirds,
Gnatcatchers, Jacamars, Motmots, Barbets, Toucans, Tapaculos,
Tinamous) underwent extensive evolutionary radiation during
Pliocene and Pleistocene (1137 species, i.e. > 10% of all species)
Continental birds
Neotropical region
• some endemic species could be relicts from former widespread
distributions
• also many endemic fresh/saltwater birds (Torrent duck,
Coscoroba swan, Steamer duck); however Cranes, Bustards,
Hornbills, Corvids, Titmice, Nuthatches, Treecreepers and Shrikes
largely absent
Continental birds
Neotropical region
• diversity due to (i) extent of rain forest, (ii) N- and S-American
fauna mixing at end Pliocene, (iii) high regional endemism, (iv)
fewer Pleistocene extinctions due to less drastic glaciations, (v)
speciation due to long isolation, (vi) pronounced altitudinal
zonations, (vii) recent human colonization
• contains ca 90% of all suboscine birds, while dominant oscines
(> 4000 species worldwide) proportionally least abundant
• ‘Great American Interchange’: more species colonized from N to
S than vice versa (Tanagers, Cardinals, Thrushes, Pipits, Horned
lark, Short-eared owl)
• flightless ratites of Africa, South America and Australia probably
remnants of former Gondwana
Continental birds
Neotropical region
• South America and Africa share various families (Trogons,
Parrots, Jacanas, Painted snipes, etc) but only 17 species; possibly
as a result of ocean crossing via stepping stones (ancient volcanos
in south Atlantic)
Continental birds
Neotropical region
• West Indies (Greater and Lesser Antilles, Hispaniola, Carribean)
have impoverished avifauna (280 breeding species, 31 endemic
genera, 150 endemic species) received by dispersal; level of
endemism surprisingly high given proximity of both North and
South America
Continental birds
Neotropical region
• Galapagos, Falklands and Juan Fernandez archipelago received
most of their fauna from adjacent parts of South America
Continental birds
Oceania
Continental birds
Oceania
• Pacific Ocean occupies > 1/3 of earth’s surface (> 166 mil km²);
more than 23.000 small (tropical and subtropical) islands, mostly
volcanic, mainly in C and SW parts of ocean
• divided into 3 regions: Micronesia and Melanesia (west) and
Polynesia (central); islands only cover 46.632 km² (> 50%
contributed by three islands; e.g. Hawaii); some coral atolls
(Tuomota archipelago) below 7m altitude
• avifauna derived by cross-water colonization; hence small
number of taxa and strong affinities with nearest continent; largest
families are Whistlers, Doves, Flycatchers, Rails, Parrots and
Honeycreepers
Continental birds
Oceania
Continental birds
Oceania
• islands fall into 5 biogeographical regions, but central Pacific ones
usually treated as Oceania; 187 landbirds in 23 families;
represents 20 x species density of richest continent; 38% genera
and 87% species endemic
• striking examples of recent species formation and faunal
attenuation, i.e. successive families, genera and species dropping
out with increasing distance from continental source
Continental birds
Oceania
• Hawaiian archipelago more than 4000 km off north America, yet
still containing most diverse island fauna; half of avian colonizers
from North America; many species extinct following human
colonization
Continental birds
Oceania
• avifauna of Oceania most severely impacted
Continental birds
Antarctica
Continental birds
Antarctica
• comprises main continent of Antarctica and all islands, sea ice
and ocean northwards to Antarctic Convergence
• remaining fragment of ancient Gondwana which drifted to
present position over south pole; colder than arctic
• 14.3 mil km² covered with thick glacial ice which is unsuitable for
birds; at the end of summer, sea freezes from shoreline outwards
(ca 3 km/day; doubling size continent by end of winter)
• no landbirds on main land-mass, seabirds dominated by Penguins
and Petrels; sub-antarctic islands (South Georgia, Kerguelen,
Macquarie) hold 4 Ducks, 1 Pipit, Common starling and Lesser
redpoll (both self-introduced from New Zealand) and introduced
Rail
• Shearwaters, Gadfly petrels and endemic landbirds north on
temperate sub-antarctic islands (Tristan da Cunha, Chatam)
Conclusions
Species numbers and diversity
• overall, about 91% of landbird species are only found in a single
biogeographical region
• moving through taxonomic hierarchy, distributions change
progressively from restricted to widespread; only 4 out of 23
landbird orders are represented in a single biogeographical region
• differences can be attributed to greater age of higher taxa and
greater opportunities through time for wider dispersal
• regions differ in numbers and densities of breeding birds and of
species per family, due to (i) different past events of autochthony,
colonization and in situ speciation (versus extinction), (ii) K-values
to support large numbers of different taxa; (iii) past extent of
glaciation; (iv) human impact
Conclusions
Species numbers and diversity
• # species/mil km²: (S) Neotropical (3370/185) > Australasian
(1592/179) > Afrotropical (1950/93); (N) Oriental (1697/177) >
Neartic (732/35) > Palaearctic (937/20)
• at higher taxonomic levels, differences between regions are less
marked, with Afrotropical region emerging as richest (breeding
species of 54% families and 83% orders)
• Neotropical region holds extremely high number of species per
family (average 47.5, Tyrannidae 544 species) and proportion of
endemic species and families; also has the most distinctive bird
fauna, followed by the Afrotropical, Australasian, Indomalayan,
Nearctic and Palaearctic
• each region has own dominant groups (large numbers of species,
large morphological and ecological diversity): North America
(Parulid warblers), South America (Tyrannid flycatchers), Eurasia
(Silviid warblers), Africa (Weaver finches), Australia (Honeyeaters)
Conclusions
Percentage of landbird orders, families and species that
breed in 1-7 biogeographical regions
Conclusions
Meeting of faunas
• continental interchange is more marked in New than Old World
due to the absence of massive east-west barriers (mountain, sea,
desert) isolating temperate from tropical avifaunas
• Tyrannidae, Vireonidae and Parulini are probably of tropical origin
whereas equivalent insectivores (Sylviidae, Muscicapidae, Turdidae
and Oriolini) are probably of Palaearctic origin
• faunal exchange is predominantly unidirectional, depending on
relative number of species in each land area and relative
competitiveness (i.e. disproportionale colonization of South
America by North American mammals)
Conclusions
Meeting of faunas
• distinctiveness biotas probably maintained by resistance to
invasion (e.g. by competition): if resident species exploit all
ecological opportunities, new species may have difficulties to
establish (especially when adapted to different faunal backgrounds)
• alternatively, local adaptation may be more important than
competition
• introduced species mainly restricted to man-made habitats,
rarely penetrating remaining natural habitats which continue to
hold native birds
• based on fossil records, (i) bird distributions have changed
greatly since the start of the Tertiary (ca 65 mil y ago) and (ii)
many endemic families once occurred in other regions as well
Island birds
Island birds
• around 1627 landbird species occur only on island (ca 17% of all
non-marine species)
• combined for all islands, overall species density nearly 4 times
greater than averaged for continents
• islands are also important for nesting seabirds (not included
above)
• percentage birds on islands is much higher than in other types of
animals due to their superior dispersal powers
• tropical Pacific islands of Oceania collectively hold greatest
density of bird species (187 endemic landbird species)
• study of island birds have had major influence on evolutionary
and biogeographical theory; behave like ‘replicated experiments’
Island birds
Island types classified according to mode of origin
Island birds
Relationships between species number, island size
and level of isolation
Island birds
Decline in occurrence of (sub)families of breeding landbirds
from New Guinea eastwards on various Pacific Islands
Island birds
Sequence of island colonisation from a
mainland source
Seabirds
Seabirds
• seabirds generally do not follow same biogeographical patterns
as landbird species
• include ca 320 species (skuas, skimmers, gulls, terns, auks,
tropicbirds, boobies, gannets, shags, cormorants, frigatebirds,
penguins, loons, petrels, shearwaters, albatrosses); 5 of 8 groups
entirely marine; distinction with landbirds not always clearcut
Seabirds
Seabird species following classification by Sibley & Monroe 1990
Seabirds
• form only 3% of world’s bird species, despite fact that sea water
covers >66% of surface; however, collective biomass probably
outweighs landbirds
• dependence on land varies between species; distribution mainly
governed by latitudinal marine zones, distribution of food within
those zones, and location of nesting places
Seabirds
Latitudinal biogeographical sea water zones
Seabirds
• Procellariiformes (petrels) are most pelagic of all seabirds
Seabirds
• capacity to exploit distant food-supplies being helped by:
(1) lower body T (38°C) and thus lower energy demands
(2) ability to lay down subdermal fat and stomach oil
(3) dynamic flight mode which additionally conserves energy
(4) ability to feed by day and night (excellent olfactory sense)
(5) ability of eggs to resist chilling and chicks to become torpid
Seabirds
• very few seabirds species compared to landbirds; 3.3% species
on 71% Earth surface
• sea is one of the least productive ecosystems per unit of surface
area (only 0.25% of primary production)
• all seabirds are carnivores (among vertebrates, species richness
of carnivores only 10% of herbivores)
• most seabirds are confined to relatively shallow coastal areas,
and all species are tied to land for breeding
Seabirds
• throughout the evolutionary history of birds, sea areas have
remained interconnected; coastlines of all main continents either
connected or within flying distance of neighbouring continents
• extreme mobility of most seabird species
• life at sea constraints body designs, colours and sizes of a birds
to a more narrow range of options
Seabirds
• seabirds may have resisted extinction partly because of:
(1) their large geographical ranges
(2) their widely separated, largely inaccessible nesting sites
(3) the fact that younger age classes of many species tend to
remain at sea away from vulnerable nesting colonies (e.g. Shorttailed albatross)