Satellite tracking of two Montagu’s Harriers (Circus pygargus): dual pathways during autumn migration
Autumn migration routes of two Dutch female Montagu’s Harriers (Circus pygargus) were documented for the first time using satellite telemetry. Both migrated to their African wintering area—one via the Straits of Gibraltar through the Mediterranean and the other via Italy/Tunisia. The rate of travel was comparable to values reported for larger raptor species.
KeywordsConnectivity Migration and food supply
Satellite tracking has proven to be a useful technique to document migratory routes of large bird species, such as White Storks (Ciconia ciconia; Berthold et al. 1992, 2004), Peregrine falcons (Falco peregrinus; Fuller et al. 1998), Ospreys (Pandion haliaetus; Hake et al. 2001; Alerstam et al. 2006) and eagle species (Meyburg et al. 1995, 2003). Western European Montagu’s Harriers (Circus pygargus) winter in different West African countries (Fransson and Petterson 2001; Arroyo et al. 2004). During the autumn migration, the proportion of Harriers passing over Gibraltar is higher than that over Italy, but the reverse pattern is observed in spring. This has led to the hypothesis of loop migration: Harriers leaving Europe via Gibraltar and returning via Italy (Agostini and Logozzo 1997; Garcia and Arroyo 1998). In 2005, Montagu’s Harriers could for the first time be tracked using satellite transmitters. Two Dutch female Harriers chose dual pathways during their autumn migration.
We used 12-g solar satellite transmitters (Microwave Telemetry, Columbia, Md.) that send signals for a 10-h period followed by a 48-h pause. Data were obtained from the Argos system via CLS (Collecte Localisation Satellites, Toulouse, France). The satellite transmitters were attached on 16 July 2005 using teflon-ribbon backpacks (M. Gschweng, personal communication; Kenward 1987; Snyder et al. 1989). The total backpack weighed less than 5% of the females’ body weight. Hereafter, we refer to the first female as Marion and the second female as Beatriz. Both females successfully bred in 2005 in the northeastern part of The Netherlands (Marion: four fledglings, Beatriz: two). Based on iris colouration observed in 2005 and before (Arroyo et al. 2004), Marion was assessed as being at least in her fifth calender year and Beatriz at least her third. STAT and Maptool software were used for analyses (Coyne and Godley 2005). Only high-quality fixes with a presumed error between 150 m and several kilometres (CLS) were included.
Results and discussion
Both females seemed to choose relatively narrow sea crossings near Gibraltar and Italy, respectively. Beatriz may have crossed the Mediterranean East of Gibraltar (140 km over the open sea; Fig. 1), as 65% of Montagu’s Harriers migrating through this region do crosse here (Meyer et al. 2000). High-quality fixes of Marion between the Czech Republic and Niger were lacking. A low-quality fix of 8 September indicated a position in Italy, with its mirror image in Greece (Fig. 1). A low-quality fix in Algeria (11 September) suggests that Marion took the route via Italy. To reach Italy via the Adriatic Sea required at least a 80-km flight over the open sea. Taking the location in Algeria into account, we assume that Marion did not fly the 480 km from Italy to Libya but arrived in Tunisia first, which means a 140-km sea crossing.
Based on studies on the Peregrine falcon and Osprey, it is known that migration is faster in the middle phase than in the beginning and at the end (Fuller et al. 1998; Kjellén et al. 2001). We observed the same seasonal pattern in terms of daily distances covered for the two Harriers: whereas in August they covered maximally just above 100 km day−1, the distances became longer in the first half of September. Marion reached her highest rate of travel above the Sahara, as has been found for Ospreys (Kjellén et al. 2001), when she travelled up to 623 km day−1 (1247 km on 16–17 September) before slowing down before she reached her first destination, Dakoro (Niger) on 21 September. Assuming a straight travel route and a constant rate of travel between Italy and Niger, crossing the Sahara would have taken her 8 days. The average daily distance Marion covered on travel days was 168 km. The average over both travel and stop-over days during the migration period was 143 km day−1. If we assume that the low-quality fixes in Italy and Algeria were correct, this travel rate would have been 160 km. Both estimates are similar to those found for heavier raptor species, such as the Greater Spotted Eagle (Aquila clanga; 150 km day−1; Meyburg and Meyburg 1999), Lesser Spotted Eagle (Aquila pomarina; 166 km day−1; Meyburg and Meyburg 1999), Peregrine falcon (172 km day−1; Fuller et al. 1998) and Osprey (183 km day−1; Alerstam et al. 2006). Marion’s maximum daily distance of 623 km was again similar to the 537 km day−1 reported for the Lesser Spotted Eagle (Meyburg and Meyburg 1999). Taking this into account, it seems likely that Montagu’s Harriers are able to migrate at similar rates of travel as the larger and heavier raptors.
Marion apparently did not engage in loop migration (at least not in the predicted direction), and this behaviour could not be evaluated for Beatriz due to the early lack of signals. The exact proportions of Western European Montagu’s Harriers that use the western or central route through the Mediterranean and the extent of migratory connectivity between different breeding and wintering areas will have to be investigated using larger sample sizes of tracked birds and ring recoveries.
Satellitentelemetrische Studie von zwei Wiesenweihen (Circus pygargys): unterschiedliche Routen auf dem Herbstzug
Der Herbstzug zweier niederländischer Wiesenweihenweibchen wurde zum ersten Mal mittels Satellitentelemetrie dokumentiert. Einer der Vögel zog über Gibraltar durch das Mittelmeergebiet, der andere zog über Italien/Tunesien in das afrikanische Überwinterungsgebiet. Tagesetappen waren vergleichbar mit Werten, die für größere Greifvögel dokumentiert sind.
Erik Visser and Marion Gschweng helped attach the transmitters. Michael Coyne, Mark Fuller, Kurt Burnham, Roy Dennis, Götz Eichhorn and Joost Brouwer provided valuable advice. Ringing licences were obtained from the Dutch Bird Ringing Centre. STAT and Maptool software were obtained from http://www.seaturtle.org. The Nederlandse Aardolie Maatschappij and AKZO-Nobel sponsored the purchase of the satellite transmitters. The Ministry of Agriculture, Nature and Food quality, the Province of Groningen, the Prince Bernhard Cultural Foundation and Vogelbescherming Nederland (BirdLife Netherlands) provided financial support. This study complies with the current laws of the Netherlands and it was approved by the Institutional Animal Care and Use Committee of the University of Groningen under licence number D4382B.
- Agostini N, Logozzo D (1997) Autumn migration of Accipitriformes through Italy en route to Africa. Avocetta 21:174–179Google Scholar
- Arroyo BE, García JT, Bretagnolle V (2004) Circus pygargus Montagu’s Harrier. BWP Update 6:41–55Google Scholar
- Fransson T, Petterson J (2001) Svensk ringmärkningsatlas. vol 1. Naturhistoriska Riksmuseet and Sveriges Ornitologiska Förening, StockholmGoogle Scholar
- Kenward R (1987) Wildlife radio tagging. Academic, LondonGoogle Scholar
- Meyburg B-U, Meyburg C (1999) S49.2: The study of raptor migration in the Old World using satellite telemetry. In: Adams NJ, Slotow RH (eds) Proc 22 Int Ornithol Congr Durban. BirdLife South Africa, Johannesburg, pp 2992–3006Google Scholar
- Millon A, Bretagnolle V, Leroux A (2004) Busard cendré Circus pygargus. In: Thiollay J-M, Bretagnolle V (eds) Rapaces nicheurs de France, distribution, effectifs et conservation. Delachaux et Niestlé, Paris, pp 70–74Google Scholar
- Snyder NFR, Beissinger SR, Fuller MR (1989) Solar radio-transmitters on snail kites in Florida. J Field Ornithol 60:171–177Google Scholar