Abstract
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.
Highlights
Understanding the conservation requirements of threatened species requires consideration of their entire annual cycle
Using location data collected from adult Black Harriers marked with GPS-GSM or PTT tracker devices and monitored during the 2008–2016 breeding and non-breeding seasons, the aims of this study were to (i) describe for the first time the overall migration patterns, (ii) identify the areas used during the breeding and non-breeding seasons and (iii) estimate the size of the settlement areas used by individuals during both the Annual movements in an intra-African migratory raptor breeding and the non-breeding seasons
One female (F6) travelled 1105 km towards the Eastern Cape where she spent a total of 11 days before returning to her former breeding area where she spent the rest of the non-breeding season
Summary
Understanding the conservation requirements of threatened species requires consideration of their entire annual cycle. 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 [4]. Most studies of bird migration have been performed on intercontinental migrants, i.e. individuals traveling thousands of kilometers from their breeding to their non-breeding areas [11,12,13,14], while species travelling shorter distances, without necessarily moving across country borders have received, by comparison, relatively less attention [14,15,16]. [24, 25]), there is an urgent need to learn more about migration routes and areas used by African raptor species throughout their annual cycle, to effectively manage and conserve these threatened populations In a context where many African raptor populations have decreased in recent decades [21, 22], mostly due to habitat fragmentation, persecution [23] and exposure to poisons and contaminants (e.g. [24, 25]), there is an urgent need to learn more about migration routes and areas used by African raptor species throughout their annual cycle, to effectively manage and conserve these threatened populations
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