Migration of the Western Marsh Harrier to the African wintering quarters along the Central Mediterranean flyway: a 5-year study

Abstract

Background:The Western Marsh Harrier (Circus aeruginosus) is a partial migrant with the populations from Eastern and Northern Europe migrating south to sub-Saharan Africa. During the autumn migration, that is peaking in September, harriers move on a broad front heading SW and undertake long sea-crossings en route to their wintering quarters, passing in substantial numbers through Italy and Malta with the highest concentrations recorded at the Strait of Messina. Most of the individuals migrating across the Strait are heading for the wintering quarters in Africa, while fewer spend the winter in Sicily. Methods:In a 5-year study (2011)(2012)(2013)(2014)(2015), between 26 August and 30 September, we determined age and sex of autumn migrating harriers through this flyway. In 2014 we determined, by marine radar and optical range finder, the flight altitude of migrating harriers.Results: A total of 10,261 Western Marsh Harriers were counted during the whole study, with an average of 2052 per autumn season. Adults outnumbered juveniles and males outnumbered females. Harriers flew at lower altitudes during the morning while large flocks flew lower than single birds or small flocks. Conclusions:Our observations are consistent with previous surveys and confirm that adult males have a tendency to migrate over a long distance, while substantial numbers of adult females and juveniles do not head for the wintering quarters in Africa. Finally, flight patterns recorded can be explained by a more pronounced flapping flight of Western Marsh Harriers during migration.

Migration pattern and wintering population of the Eurasian marsh harrier (Circus aeruginosus) in the Central Marshes, a wetland of international importance in southern Iraq

“…This is in accordance with the "body size hypothesis" about smaller and lighter males migrating over longer distances (Agostini et al 2003). The males' tendency towards longdistance movements has been attributed to the higher proportion of males' flapping flight (Spaar & Bruderer 1997), or their avoidance of intraspecific sex competition with larger females, which are capable of capturing larger prey, tolerating cold climates, and enduring starvation (Agostini et al 2017). However, our conclusion was based on a single observation of an adult male in September with no further records in October, which is rather scarce data to support our claim and requires further investigation.…”

“…Our results are in agreement with those for marsh harriers migrating across the Falsterbo Peninsula in Sweden (western Europe) in autumn, where juveniles (n = 1594, 78%) outnumbered adult females (n = 273, 13%) and adult males (n = 216, 9%) (Kjellén1992). In contrast, adult marsh harriers were observed in greater numbers than juveniles along the Central Mediterranean flyway (Agostini et al 2017). Furthermore, our observations suggest that migrating juveniles arrive in the Central Marshes earlier than adults, as their numbers gradually increased from September-January (7-21) respectively.…”

“…There is a scarcity of information concerning raptor migration in Iraq and the Middle East generally (Shirihai & Christie 1992, Shirihai et al 2000. Our results suggest that the autumn migration of the Eurasian marsh harrier in the Central Marshes starts in early September, when increasing numbers of migrants emerge, similar to those migrating from western and eastern Europe across subSaharan Africa (Strandberg et al 2008, Agostini and Panuccio 2010, Agostini et al 2017. The premigration movement strategies adopted by the genus Circus are used to reduce intraspecific competition, ensuring sufficient resources for moulting or recovering from breeding efforts, and for preparing for migration (Limiñana et al 2008, Triewieler et al 2008.…”

“…Ring recoveries show that adult marsh harriers tend to engage in autumn migration slightly earlier than juveniles (Strandberg et al 2008), similarly to those crossing on the Central Mediterranean flyway (e.g. Agostini et al 2017). However, marsh harriers from western Europe migrating across the Sahara Desert showed no distinct differences between sexes, timing, duration or speed of autumn and spring migrations, except that adult females tended to migrate faster than males in spring (Strandberg et al 2008, Panuccio et al 2013a.…”

“…Adults may be less inclined to follow major flyways during migration, however, the differential timing between juveniles and adult females (P < 0.05) and that between adult females and males (P < 0.001) migrating over the Falsterbo Peninsula is significant (Kjellén1992). Conversely, marsh harriers from western and eastern Europe need to refuel at several stopover sites before crossing the Mediterranean Sea in a longdistance energy consuming migration (Agostini et al 2017). Ring recoveries show that adult marsh harriers tend to engage in autumn migration slightly earlier than juveniles (Strandberg et al 2008), similarly to those crossing on the Central Mediterranean flyway (e.g.…”