Areas

Patterns in distribution

By definition, resident bird populations occupy the same geographical range year-round, while migratory species occupy partly or wholly different ranges at different times of year. The variations are in the degree of separation of breeding and wintering ranges, from coincident, through overlapping, to completely

1Three species of Palaearctic migrants have recently been recorded breeding in their South African winter quarters, namely White Stork Ciconia ciconia, Whiskered Tern Chlidonias hybridus and Black-necked Grebe Podiceps nigricollis, while the Common Sandpiper Actitis hypoleucos has bred in various parts of East Africa. Other species, possibly derived from migrants, are now resident or migratory within southern Africa, namely Great-crested Grebe Podiceps cristatus, Black Stork Ciconia nigra, Booted Eagle Hieraaetus pennatus, Pied Avocet Avosetta avosetta, Black-winged Stilt Himantopus himantopus, European Bee-eater Merops apiaster, Alpine Swift Apus melba and Common Stonechat Saxicola torquata. Two others have subspeciated, namely the African Bittern Botaurus stellaris and Mountain Buzzard Buteo b. oreophilus. So perhaps migrants have been colonising southern Africa for a long time. The Barn Owl Tyto alba is also resident, but is almost cosmopolitan and did not necessarily derive from European migrants.

1. Resident year-round throughout the entire latitudinal span of the range.

3. Present year-round only in the northern part of the range, and in winter only in the southern part.

1. Resident year-round throughout the entire latitudinal span of the range.

2. Present in summer only in the northern part of the range, and year-round in the southern part.

3. Present year-round only in the northern part of the range, and in winter only in the southern part.

4. Present in summer only in the northern part of the range, year-round at intermediate latitudes, and in winter only in the southern part.

5. Summer range immediately to the north of the winter range, with little or no overlap.

Figure 13.7 Main migration patterns found in northern hemisphere birds, based on the degree of separation between breeding and wintering ranges. See also Table 13.2.

6. Summer range separated from winter range by a latitudinal gap in which the species occurs only on passage.

separate (Figure 13.7; Table 13.2). In most species, breeding and wintering ranges are coincident or overlapping, while smaller numbers show a latitudinal gap between the two, differing in extent between species (Figure 13.8).

In both Old and New Worlds the greatest separation of breeding and wintering ranges is found, as expected, in species that breed only at high latitudes in one hemisphere and winter only at high latitudes in the opposite hemisphere. Among landbirds, the Swainson's Hawk Buteo swainsoni is one of the most extreme examples, as it breeds between 25° and 65°N in North America and winters between 24° and 40°S in South America, giving a 49° latitudinal gap between the breeding and wintering ranges (apart from small numbers that winter in some southern States). Among seabirds, the Arctic Tern Sterna paradisaea is probably

Table 13.2 Migration patterns of birds in the northern hemisphere, arranged roughly in order of increasing segregation of breeding and wintering ranges

Total no. in each categorya

1. Present year-round throughout their whole latitudinal range

2. Present only during the summer breeding season in the north of their range, year-round in the south

3. Present year-round in the north of the range, only during winter in the south

4. Present only during the summer breeding season in the north of their range, year-round at intermediate latitudes, and only during winter in the south

Old World examples: Black Grouse Tetrao tetrix, Eurasian Green 195

Woodpecker Picus viridis, Black-billed Magpie Pica pica, House Sparrow Passer domesticus

New World examples: Ruffed Grouse Banasa umbellus, Northern 64

Bobwhite Colinus virginianus, Common Raven Corvus corax, Carolina Wren Thryothorus ludovicianus

Old World examples: Common Wood-pigeon Columba palumbus, 22

Eurasian Skylark Alauda arvensis, European Serin Serinus serinus, European Robin Erithacus rubecula

New World examples: Red-tailed Hawk Buteo jamaicensis, Common 47 Moorhen Gallinula chloropus, Blue Jay Cyanocitta cristata, Common Grackle Quiscalus quiscula

Old World examples: Eurasian Blackbird Turdus merula, Siberian 21

Tit Parus cinctus, Willow Tit Parus montanus, Pine Grosbeak Pinicola enucleator

New World examples: Evening Grosbeak Hesperiphona vespertina, 23

House Finch Carpodacus mexicanus

Old World examples: Eurasian Woodcock Scolopax rusticola, 111

Rook Corvus frugilegus, Redwing Turdus iliacus, Common Starling Sturnus vulgaris

New World examples: Canada Goose Branta canadensis, 52

Short-eared Owl Asio flammeus, Cooper's Hawk Accipiter cooperii, Song Sparrow Melospiza melodia

5. Summer breeding range immediately to the north of the wintering range

6. Summer breeding range separated geographically from the wintering range by a gap in which the species occurs only on passage. Some of these species cross large stretches of inhospitable sea or desert in which they cannot feed during migration

Old World examples: Ruddy Turnstone Arenaria interpres, 22

Great-spotted Cuckoo Clamator glandarius, Bluethroat Luscinia svecica, Ring Ouzel Turdus torquatus

New World examples: Red-breasted Merganser Mergus serrator, 34

House Wren Troglodytes aedon, Yellow-throated Warbler Dendroica dominica, Vesper Sparrow Pooecetes gramineus

Old World examples: Arctic Tern Sterna paradisaea, Eurasian 117

Dotterel Eudromias morinellus, Sanderling Calidris alba, Red-footed Falcon Falco vespertinus, Lesser Grey Shrike Lanius minor, Icterine Warbler Hippolais icterina

New World examples: Whistling Swan Cygnus c. columbianus, 144

Brent Goose Branta bernicla, Swainson's Hawk Buteo swainsoni, Long-tailed Jaeger Stercorarius longicaudus, Iceland Gull Larus glaucoides, Baird's Sandpiper Calidris bairdii, Bristle-thighed Curlew Numenius tahitiensis, Snow Bunting Plectrophenax nivalis

See also Figure 13.7.

aThe proportions in the six categories differ significantly between western Europe-Africa and eastern North America-South America (x5 = 85.7, P < 0.001), reflecting mainly the smaller proportions of class 1 species, and the greater proportions of classes 5 and 6 species, in North America. The three species of southern hemisphere seabirds that spend the northern summer (austral winter) off Europe, and the eight that spend the northern summer off eastern North America, are excluded from analysis.

C 0 A 5 10 15 20 25 30 35 40 45 50 55 Degree gap between breeding and wintering ranges

Figure 13.8 Frequency distribution of latitudinal gaps between breeding and wintering ranges, calculated for west Palaearctic breeding birds. C, coincident; O, overlapping; A, adjacent.

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