Factors affecting breeding success of Peregrine and Lanner Falcons in South Africa

Breeding success was recorded for three Peregrine Falcon, Falco peregrinus, populations in South Africa over nine years, and for Peregrine and Fanner Falcon, F. biarmicus, populations in on area of sympatry over three years. The objectives of the study were to; :measure geographic and interspecific variation in reproductive performance, and determine environmental correlat es of productivity. Territory occupancy, the frequency of breeding per occu pied territory and clutch size did not vary significantly between the three Peregrine populations. However, Peregrine breeding success was generally l ower on the Cope Peninsula (1.11 young fledged per territorial pair), highe r in the Soutpansberg (1.35) and highest on the Orange River (1.70). Overal l, fledging rates of Soutpansberg Peregrines and Lanners were not significa ntly different, although annual productivity of the Lanner papulation was c onsistently higher. Neither species' breeding success was significantly dep ressed by the presence of close neighbouring pairs of the other, suggesting that they were not active competitors, Breeding performance of Peregrine; on the Cope Peninsula correlated strongly with spring weather conditions: e gg and hatchling survival was lower in wet years, and fledging rates were h igher in warm years. Annual productivity of Orange River Peregrines correla ted positively with the height of the river at the onset of breeding, and p roductivity of Soutpansberg Peregrines was higher in seasons following year s of high rainfall. Elements of the physical structure of the nesting habit at (exposure of the nest ledge, height of the nest cliff) correlated positi vely with Peregrine breeding performance. Breeding success of Soutpansberg Lanners was largely unaffected by any of the environmental variables consid ered. Overall, it is proposed that Peregrine productivity reflected variati on in the physical environment and its affect on prey availability.