Abstract :
Stable isotopes (dD, d13C, d15N) were measured in adult and juvenile Amur Falcon Falco
amurensis feathers to understand the migratory connectivity of this species. Using the OIPC
(Online Isotopes in Precipitation Calculator) and a calibration curve for American Kestrels Falco
sparverius we predicted the breeding range of South African Amur Falcons in the Palaearctic. dD
values for juvenile feathers (mean 6 SE 5 58.1 6 2.5&, range 83.9 to 25.7&) and
predicted Palaearctic annual precipitation values indicated that juvenile Amur Falcons in South
Africa originated from across their entire Palaearctic range. This rejects the leapfrog migration
hypothesis and suggests the widespread movement of birds south, with a funnelling effect into
the subregion where they become concentrated over a narrower distribution range. Adult dDf
values were more depleted (37.4 6 1.8&, range 5 71.3 to 9.3&) than predicted annual
precipitation values for sites where feathers moulted in South Africa (20.2 6 0.9&) but there
was no correlation between dDp and dDf. This, together with significant variation of d13C among
sites and annual fluctuations in roost sizes, suggests that roost site fidelity is low in the
overwintering range. Populations not confined to breeding sites in South Africa are able to move
widely across the subregion, feeding on a broad range of arthropods that become seasonally
abundant during the austral summer. Total population estimates for South Africa are
significantly lower than global estimates so a significant proportion of the population may not
overwinter in South Africa or global populations are significantly lower than estimated. In South
Africa, roosts that number hundreds to thousands of individuals are often in large exotic trees,
e.g. Eucalyptus sp. They are often tolerant of disturbance at roosts which may be of little concern
for their conservation. Habitat changes in the overwintering range in South Africa though,
particularly due to agriculture, afforestation and strip mining, may affect global population
numbers. There is also concern over the persecution of birds along their migratory route.
