The Lesser Spotted Eagle Aquila pomarina (hereafter LSE) is a medium-sized migratory raptor that breeds mainly in central and eastern Europe. The breeding population consists of approximately twenty thousand pairs (BirdLife International 2004). The birds leave the breeding grounds from early September to early October and most of them return during April. The species winters in eastern and southern Africa, south of the Equator (Ferguson-Lees & Christie 2001).

The LSE migrates to the winter quarters following the eastern Mediterranean corridor, through the Caucasus, Turkey and the Middle East (Bijlsma 1987), a route that has been confirmed by means of satellite telemetry (e.g. Meyburg et al. 1995). In the Central Mediterranean the species is considered rare on migration (Kisling et al. 1994). There are few published records in the western Mediterranean. In Spain, recent observations were restricted to the Balearic Islands and Doñana (De Juana 2006, Rüegg 2007). For the Strait of Gibraltar there is a single possible observation in October 1976 (Bernis 1980). The species is listed as Rare by the Spanish Rarities Committee (Clavell et al. 2005). In Morocco, it is an accidental visitor, with one record only (a subadult on 18 April 1996; Thévenot et al. 2003).

The aim of this study is to demonstrate its regular occurrence and autumn migration pattern in the Strait of Gibraltar. We also present the first records of satellite tracked birds migrating through the Iberian Peninsula and northwestern Africa.

Methods

The Strait of Gibraltar is located at the southernmost point of the Iberian peninsula. The Strait is an approximately 20 km-long channel that connects the Atlantic Ocean and the Mediterranean Sea and that separates Europe from Africa (Fig. 1). This short sea-crossing makes the Strait an important migration bottleneck, channelling the majority of thermal-using migratory raptors of Western Europe. At this site, we monitored raptor migration from July to October 1998–2009. Daily censuses were carried out between 7:00 and 16:00 UTC during 68–87 days per year (on average 77 days/year), depending on weather conditions. Three strategic vantage points with a good view along the northern coast of the Strait were used for counting (Fig. 1). At least two observers per watch site continuously scanned the sky with binoculars; a telescope was used to aid identification. For each migratory raptor we recorded time, species, number of birds, direction, and age and sex (when possible). Climatic conditions were measured every second hour; when wind speed exceeded 60 km/h (c. 7 Bt) we interrupted the survey.

All records used in this study refer to positive identifications by experienced birdwatchers. We considered juveniles to be birds in fresh plumage with a wing band formed by the pale tips of the upper primary and greater coverts, and non-juveniles (either adults or immatures) as those in active moult or in worn plumage with uniformly coloured remiges (see Forsman 2007 for detailed information).

Figure 1.

Breeding range of Lesser Spotted Eagle (modified from Riede 2004), study area and observatories used in the monitoring program. Altitudinal lines (m) are indicated.

As supplementary information we used the data provided by a long-term project in which 74 birds (39 adults and 35 nestlings) were fitted with satellite transmitters (PTTs) in 1992–2009, the majority in Germany at the north-western edge of the species' breeding range (Meyburg & Meyburg 2007). From 2004 onwards the devices deployed were GPS enhanced PTTs. The tags were programmed to record a GPS fix every hour, transmitting information on flight altitude, speed and direction. Additionally, in 2009 twelve young Latvian Lesser Spotted Eagles, taken to Germany as part of a translocation project (Meyburg et al. 2008), were fitted with PTTs and released into the wild at a hacking station some 60 km north of Berlin.

Results

From 1998 to 2009 a total of 47 LSEs were observed, with annual sightings (Fig. 2). The birds were observed between 6 August and 12 October, with an average and modal date of passage of 16 and 12 September respectively (Fig. 3). The peak of migration occurred between 5 and 24 September (55% of all records). Most of the birds (n = 35) were observed in the central area of the Strait of Gibraltar (Cazalla and Tráfico observatories, Fig. 1), where the largest survey effort was conducted. The birds passed between 7:00 and 16:00 h (UTC), the majority (64% of n = 47) between 9:00 and 12:00 h. Of thirteen age-identified LSEs, ten birds were nonjuveniles.

Figure 2.

Number of Lesser Spotted Eagles registered at the Strait of Gibraltar during autumnal migration counts in 1998-2009 (n = 47).

Figure 3.

Seasonal pattern of Lesser Spotted Eagle passage at the Strait of Gibraltar (mean number/10-day, n = 47), summed for 1998–2009.

Discussion

The regular presence of LSE, albeit in small numbers, suggests an unknown migration route via the Iberian Peninsula and the Strait of Gibraltar. The number of birds crossing to Africa via the Strait of Gibraltar is probably underestimated, mainly due to methodological and identification problems. Information from satellite tracking further suggests that these birds originate from the western limit of its breeding distribution, mainly northeastern Germany and western Poland, possibly including Central Slovakia, southwest Hungary and northern Croatia. The wintering sites of these birds are still a mystery. The bird tracked as far as Ivory Coast might still have been migrating at the time of its loss. At present, there is no information to suggest that West Africa is a regular wintering site of any importance (Ferguson-Lees & Christie 2001), nor that it has been in the recent past when LSE was slightly more common in the western parts of its breeding range (Brown et al. 1982).

We show that the species has occurred annually in the Strait of Gibraltar at least since 1998, which makes a revision of its status in the western Mediterranean necessary, particularly for the Iberian Peninsula and Morocco. Furthermore, the presence of non-juveniles birds shows that the movements are not just naive juveniles on the wrong track. These results suggest two alternative hypotheses: 1) this route might be of recent origin, or 2) it is a relict of a once frequently used route, when the range of LSE expanded well into West Europe and numbers were higher (e.g. Meyburg et al. 2004). This route may have implications for the conservation of this endangered species, and it should be considered in the European recovery plans of the species, especially those focused on the dwindling westernmost populations (which are most likely to be involved in the western route).

The Programa Migres, on which the present study is based, is promoted by the Consejería de Medio Ambiente (Junta de Andalucía). We thank all volunteers that participated in the programme. The satellite tracking was financed in 2007 and 2008 by Deutsche Bundesstiftung Umwelt and Deutsche Wildtier Stiftung. We particularly acknowledge Rob G. Bijlsma for many helpful comments.