Post-fledging dependence and dispersal in hacked and wild Montagu's Harriers Circus pygargus

We compared the post-fledging dependence period, dispersal patterns and res ighting rates of captive-raised and hacked Montagu's Harriers Circus pygarg us with those of wild reared and naturally fledged Montagu's Harriers, in o rder to assess the validity of hacking as a release technique for this spec ies. Among hacked birds, we found significant relationships between the len gth of the dependence period and both hatching date and body condition (bir ds hatched later in the season had shorter periods of dependence; birds in poorer condition had longer periods of dependence). The condition index inc reased with the amount of time spent in captivity. The length of the depend ence period did not differ significantly between released and naturally fle dged birds, when hatching dates were accounted for. Observation rates of wi ng-tagged fledglings in years after marking were higher for released birds (15.5-20.9%) than for naturally fledged birds (9.4-9.9%). Released birds al so tended to be resighted closer to their released location than did the na turally fledged birds. We suggest that the differences in resighting data a re related to the better condition of the released birds, compared with the ir wild counterparts. We conclude that hacking is apparently a good release technique for captive-reared Montagu's Harriers, and that comparisons of b ehaviour at the post-fledging period may be a valid method for evaluating t he success of release techniques.