Date Published: January 17, 2019
Publisher: Public Library of Science
Author(s): Marie-Sophie Garcia-Heras, Beatriz Arroyo, François Mougeot, Keith Bildstein, Jean-François Therrien, Robert E. Simmons, Antoni Margalida.
Annual movements have been widely described for birds migrating across the Americas and between Eurasia and Africa, yet relatively little information exists for intra-African migrants. Identifying the areas used throughout a species annual cycle by understanding migratory patterns and settlement areas during breeding and non-breeding seasons is essential for conservation initiatives. Here, we describe for the first time, the migratory patterns and settlement areas of an endangered raptor endemic to Southern Africa, the Black Harrier (Circus maurus). From 2008 to 2015, thirteen breeding adult Black Harriers were trapped in south-western South Africa and fitted either with a GPS-GSM or with a PTT tracker device. Adults were monitored for 365 ± 198 days (range: 56–819 days) revealing great individual variability in annual movements. Most Black Harriers performed an unusual West-East migration from their breeding areas, but routes of all migrating individuals covered the entire southern land area of South Africa and Lesotho. The distance travelled averaged 814 ± 324 km, but unlike many other species, migrants travelled faster during post-breeding (i.e. austral summer) (207.8 ± 113.2 km.day-1) than during pre-breeding (i.e. austral winter/spring) migrations (143.8 ± 32.2 km.day-1). Although most marked individuals displayed movements similar to those that bred following pre-breeding migrations, only two of thirteen were confirmed as breeders the year after being tagged. This suggests that individuals may sometimes take a sabbatical year in reproduction, although this requires confirmation. Most tagged birds died on migration or during the non-breeding season. Adults frequently returned to the same non-breeding settlement areas, and often used up to 3 different locations an average of about 200 km apart. On the other hand, there was wide variation in distance between subsequent reproductive events. We discuss the implications of our study for the conservation of Black Harriers and more broadly for intra-African bird migrants.
Understanding the conservation requirements of threatened species requires consideration of their entire annual cycle. The non-breeding period, including migrations to and from non-breeding areas for migratory species, is a critical time for many animals, during which individuals may face harsh environmental conditions or reduced resource availability ultimately affecting their survival [1, 2]. Paradoxically, the vast majority of the studies investigating the ecology of species focus on their breeding seasons despite the fact that migrants spend the majority of their annual cycle en route or in their non-breeding areas [2, 3], a period when mortality is frequent . Additionally, conditions encountered outside the breeding area may affect reproduction through carry-over effects on body condition and arrival date back to the breeding grounds [5, 6]. Identifying areas used throughout the annual cycle is therefore critical as this helps identify limiting factors outside the breeding areas, which may be essential for understanding population processes [2, 7–10].