Dispersal of Sparrowhawks between Birthplace and Breeding Place

SUMMARY (1) Most sparrowhawks settled to breed in the general area where they were born, and recoveries fell off rapidly with increasing distance from the birthplace. Dispersal occurred in all directions, and no evidence was found for return migration. (2) In general, cocks moved less far from birthplace than did hens, with median (and maximum) distances of 14 (and 185) km for cocks and 27 (and 265) km for hens. These distances could be compared with a minimum between territories of 0.4 km. (3) Most sparrowhawks made the main movements of their lives in August/September, within a few weeks (in some cases days) of leaving their parents' territories, and probably stayed in the same general area thereafter. Very few individuals made long movements in adult life. (4) Changes in the median dispersal distances from year to year did not correlate with changes in population densities. Years when many cocks were recovered at long distances were not always the same as years when many hens were recovered at long distances. (5) Within each sex, young born in upland habitats tended to disperse further than young born in lowland. However, in neither sex were the distances moved by individuals significantly related to the grade of territory where they were born, to brood-size, or to fledging date in the season. (6) In both sexes, young which moved long distances seemed to perform less well in later life than young which moved short distancwes. Th se tendencies were significant only in hens, and only in quality of breeding habitat, layir g date and clutch size, which were themselves probably interrelated. (7) In distance, but not in direction, movements by brood-mates were highly correlated with one another, the young from some nests making short movements and from other nests long movements (the sex difference was still maintained). Distances moved by young from the same mother in different yea rs were also correlated, but not the distances moved by parents and offspring. Experience :n the first few weeks of life was probably important in influencing the distance moved, but we could not rule out inheritance too. SUMMARY (1) Most sparrowhawks settled to breed in the general area where they were born, and recoveries fell off rapidly with increasing distance from the birthplace. Dispersal occurred in all directions, and no evidence was found for return migration. (2) In general, cocks moved less far from birthplace than did hens, with median (and maximum) distances of 14 (and 185) km for cocks and 27 (and 265) km for hens. These distances could be compared with a minimum between territories of 0.4 km. (3) Most sparrowhawks made the main movements of their lives in August/September, within a few weeks (in some cases days) of leaving their parents' territories, and probably stayed in the same general area thereafter. Very few individuals made long movements in adult life. (4) Changes in the median dispersal distances from year to year did not correlate with changes in population densities. Years when many cocks were recovered at long distances were not always the same as years when many hens were recovered at long distances. (5) Within each sex, young born in upland habitats tended to disperse further than young born in lowland. However, in neither sex were the distances moved by individuals significantly related to the grade of territory where they were born, to brood-size, or to fledging date in the season. (6) In both sexes, young which moved long distances seemed to perform less well in later life than young which moved short distancwes. Th se tendencies were significant only in hens, and only in quality of breeding habitat, layir g date and clutch size, which were themselves probably interrelated. (7) In distance, but not in direction, movements by brood-mates were highly correlated with one another, the young from some nests making short movements and from other nests long movements (the sex difference was still maintained). Distances moved by young from the same mother in different yea rs were also correlated, but not the distances moved by parents and offspring. Experience :n the first few weeks of life was probably important in influencing the distance moved, but we could not rule out inheritance too. SUMMARY (1) Most sparrowhawks settled to breed in the general area where they were born, and recoveries fell off rapidly with increasing distance from the birthplace. Dispersal occurred in all directions, and no evidence was found for return migration. (2) In general, cocks moved less far from birthplace than did hens, with median (and maximum) distances of 14 (and 185) km for cocks and 27 (and 265) km for hens. These distances could be compared with a minimum between territories of 0.4 km. (3) Most sparrowhawks made the main movements of their lives in August/September, within a few weeks (in some cases days) of leaving their parents' territories, and probably stayed in the same general area thereafter. Very few individuals made long movements in adult life. (4) Changes in the median dispersal distances from year to year did not correlate with changes in population densities. Years when many cocks were recovered at long distances were not always the same as years when many hens were recovered at long distances. (5) Within each sex, young born in upland habitats tended to disperse further than young born in lowland. However, in neither sex were the distances moved by individuals significantly related to the grade of territory where they were born, to brood-size, or to fledging date in the season. (6) In both sexes, young which moved long distances seemed to perform less well in later life than young which moved short distancwes. Th se tendencies were significant only in hens, and only in quality of breeding habitat, layir g date and clutch size, which were themselves probably interrelated. (7) In distance, but not in direction, movements by brood-mates were highly correlated with one another, the young from some nests making short movements and from other nests long movements (the sex difference was still maintained). Distances moved by young from the same mother in different yea rs were also correlated, but not the distances moved by parents and offspring. Experience :n the first few weeks of life was probably important in influencing the distance moved, but we could not rule out inheritance too. SUMMARY (1) Most sparrowhawks settled to breed in the general area where they were born, and recoveries fell off rapidly with increasing distance from the birthplace. Dispersal occurred in all directions, and no evidence was found for return migration. (2) In general, cocks moved less far from birthplace than did hens, with median (and maximum) distances of 14 (and 185) km for cocks and 27 (and 265) km for hens. These distances could be compared with a minimum between territories of 0.4 km. (3) Most sparrowhawks made the main movements of their lives in August/September, within a few weeks (in some cases days) of leaving their parents' territories, and probably stayed in the same general area thereafter. Very few individuals made long movements in adult life. (4) Changes in the median dispersal distances from year to year did not correlate with changes in population densities. Years when many cocks were recovered at long distances were not always the same as years when many hens were recovered at long distances. (5) Within each sex, young born in upland habitats tended to disperse further than young born in lowland. However, in neither sex were the distances moved by individuals significantly related to the grade of territory where they were born, to brood-size, or to fledging date in the season. (6) In both sexes, young which moved long distances seemed to perform less well in later life than young which moved short distancwes. Th se tendencies were significant only in hens, and only in quality of breeding habitat, layir g date and clutch size, which were themselves probably interrelated. (7) In distance, but not in direction, movements by brood-mates were highly correlated with one another, the young from some nests making short movements and from other nests long movements (the sex difference was still maintained). Distances moved by young from the same mother in different yea rs were also correlated, but not the distances moved by parents and offspring. Experience :n the first few weeks of life was probably important in influencing the distance moved, but we could not rule out inheritance too.