Migratory connectivity and conservation of the Amur Falcon Falco amurensis: a stable isotope perspective

Stable isotopes (delta D, delta C-13, delta N-15) 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. OD values for juvenile feathers (mean +/- SE = -58.1 +/- 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 delta D-f values were more depleted (-37.4 +/- 1.8 parts per thousand, range = -71.3 to -9.3 parts per thousand) than predicted annual precipitation values for sites where feathers moulted in South Africa (-20.2 +/- 0.9 parts per thousand) but there was no correlation between delta D-p, and delta D-f. This, together with significant variation of delta C-13 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.