N

in the same way for all studies. In some cases, therefore, the figures may differ slightly from those given in the original publica-followed by car and plane.

Box 8.3 Migrations of Peregrine Falcons Falco peregrinus and Swainson's Hawks Buteo swainsoni from North America. From Fuller et al. (1998)

1. Peregrine Falcon. Sixty-one adult female Peregrines were tracked on migration between nest-sites in northern North America or Greenland and wintering sites in southern North America, Central and South America (Figure 8.6). Breeding sites spanned about 35° of latitude and wintering sites about 80° of latitude (from 40°N in the mid-Atlantic United States coast to 40°S in central Argentina). On average, on their southward journey these birds covered 8624 km and on their northward journey 8247 km (taking slightly different routes at the two seasons).

Figure 8.6 Migration routes of Peregrine Falcons Falco peregrinus (above) and Swainson's Hawks Buteo swainsoni (overleaf) from North American breeding areas, as shown by the tracks of satellite-tracked radio-marked adults. See also Box 8.3. From Fuller et al. (1998).

Their southward journey took an average of 50 days at around 172 km per day, and their northward journey took an average of 42 days at around 198 km per day. In general, these birds migrated on a broad front, but in autumn tended to concentrate along coastal routes, and many crossed the Gulf of Mexico and Caribbean. In spring they took more inland routes, on the western side of the Gulf, from which they headed towards various northern destinations. Birds migrating north through a single locality (Padre Island on the Texas coast) diverged for destinations ranging from Alaska to west Greenland. These findings confirmed those obtained over a longer period from ringing, i.e. that many individual Peregrines which migrate southward down the east coast of North America in autumn migrate northward up the Gulf Coast in spring, performing a 'loop migration' like many shorebirds.

2. Swainson's Hawk. In contrast to Peregrines, Swainson's Hawks migrate by soaring flight and converge on a relatively narrow route from North to South America through Panama, thus avoiding sea-crossings and showing no great divergence of routes between spring and autumn

(Figure 8.6). Of 34 birds tracked from various localities in the breeding range in western North America, all wintered in a relatively small area in South America lying at 30°-40°S and 61°-64°W. On average, these birds travelled 13 504 km on their southward journey, at 188 km per day, and 11 952 km on their northward journey, at 150 km per day. On southward migration, the birds became concentrated on the Gulf Coast of Central Mexico, and remained in a relatively narrow stream through Panama and down the eastern flanks of the Andes.

Figure 8.7 Migration routes of a mated pair of Greater Spotted Eagles Aquila clanga from a nestsite in Poland to wintering sites in Africa. Note that the two mates spent the non-breeding period in widely separated areas. From Meyburg et al (1998).

To save cost and battery power, most raptors on migration were satellite-checked every few days, but Meyburg et al. (1998) monitored a Short-toed Eagle Circaetus gallicus every night on its autumn journey between France and Niger in West Africa. They were thus able to record every roost location, and the distances travelled each day throughout the journey. These daily distances varied from 17 to 467 km (mean 234 km), and the whole 4685 km journey took 20 days (Figure 8.9). Other raptors for which sufficient data were obtained have occasionally moved more than 400 km per day, with 746 km recorded from an Osprey Pandion haliaetus through Europe (Kjellen et al. 2001), and 537 km for a Lesser Spotted Eagle Aquila pomarina through Africa (Meyburg et al. 2001), as well as the 435 km for the Bald Eagle Haliaetus leucocephalus that migrated within a day (Grubb et al. 1994).

Not surprisingly, those species tracked between Europe and Africa travelled more rapidly over the Sahara (which probably offered excellent soaring conditions but no food) than over other parts of the journey (for Short-toed Eagle Circaetus gallicus see Meyburg et al. 1998, for Osprey Pandion haliaetus see Kjellen et al. 2001, for Honey Buzzard Pernis apivorus see Hake et al. 2003). Elsewhere some species broke their autumn journeys for up to several weeks at a time, apparently when they encountered good feeding areas. Once in winter quarters, individuals of most species remained in one place throughout their stay, and those individuals studied in successive years returned to the same breeding and wintering localities each year (e.g. Meyburg et al. 1998). However, an adult female Wahlberg's Eagle Aquila wahlbergi tracked from its breeding area in Namibia to a non-breeding area centred mainly in Nigeria wandered over a large area there of 60 000 km2 (Meyburg et al. 1995b). Similarly, some Lesser Spotted Eagles A. pomarina wandered over a large area in southern Africa, frequently making extensive moves during the course of their stay (Meyburg et al. 1995c, 2004b). This species is

Distance (km)

Figure 8.8 Relationships between duration and distance in the autumn migrations of different raptor species, based on the mean values from different studies listed in Table 8.3. Regression relationship: Duration (days) = 11.8 + 0.00493 x distance (km), r = 0.75, P < 0.001. No significant relationship emerged between migration speed and distance: speed (km per day) = 116 + 0.0057 x distance (km), r = 0.31, P = 0.162.

Distance (km)

Figure 8.8 Relationships between duration and distance in the autumn migrations of different raptor species, based on the mean values from different studies listed in Table 8.3. Regression relationship: Duration (days) = 11.8 + 0.00493 x distance (km), r = 0.75, P < 0.001. No significant relationship emerged between migration speed and distance: speed (km per day) = 116 + 0.0057 x distance (km), r = 0.31, P = 0.162.

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