Translator Disclaimer
1 October 2010 Successful Breeding of a Ten-Year-Old Hybrid Spotted Eagle Aquila clanga × A. pomarina Retaining Immature Plumage Characters
Ülo Väli
Author Affiliations +
Abstract

Greater Spotted Eagle Aquila clanga and Lesser Spotted Eagle Aquila pomarina are hybridising Eurasian raptors, but our knowledge of hybrid fertility is poor. Here, I present a case of interbreeding between a F1 hybrid spotted eagle male and a Lesser Spotted Eagle female in Estonia. The hybrid was first studied and ringed as a nestling in 1999, showing characters of both species. In 2009, the same bird was caught and, surprisingly, this ten-year-old individual had retained several immature characters. Again, characters of both species were recorded in the hybrid, as well as in his backcross-offspring. At the nest site level, the habitat of the hybrid's hatching site was intermediate but its nesting site was typical of A. pomarina. At the landscape level hatching and breeding sites resembled habitat typical of A. clanga in Estonia.

The ranges of Greater Spotted Eagle Aquila clanga and Lesser Spotted Eagle Aquila pomarina overlap in Eastern Europe, where interspecific hybridisation has been recorded repeatedly (Bergmanis et al. 1997, Lõhmus & Väli 2001, Bergmanis & Strazds 2001, Väli & Lõhmus 2004, Dombrovski 2005, Meyburg et al. 2005b, Treinys 2005, Schwanbeck 2008). Although field observations and genetic analyses suggest that at least some hybrids are fertile (Väli & Lõhmus 2004, Dombrovski 2005, Helbig et al. 2005, Väli et al. 2010b), verified cases with detailed descriptions are lacking. Knowledge on fertility of hybrids is important for both theoretical (e.g. taxonomical) and conservation reasons.

In the current study, I describe a male hybrid spotted eagle, breeding with a female A. pomarina in Estonia, as well as his two offspring, backcrosses between hybrid and A. pomarina, using a number of species-specific morphological characters proposed by Bergmanis (1996), Forsman (1999), Väli & Lõhmus (2004) and Dombrovski (2006). Measurements were taken following Bergmanis (1989) and Baker (1993). As comparisons of natal and breeding sites of eagles are scarce, I also give detailed descriptions of the two nest sites using the same parameters as in previous papers (Treinys 2004, Väli et al. 2004, Lõhmus & Väli 2004, 2005, Mirski 2009).

Results

On 20 July 1999, a spotted eagle nestling was studied and ringed (Estonia Matsalu R7400, hereafter R7400) at its nest in east-central Estonia. According to the DNA-analysis (see for method: Griffiths et al. 1998 and Väli 2004), the nestling was a male. In general, its plumage was typical of A. pomarina: a large ochre nape patch, brown body colour, few yellowish spots on medium upperwing coverts and contrasting bars on rectrices. However, typical of A. clanga, he had rather narrow dark bands on the secondaries (though not as narrow as in most A. clanga) and a large bill (Table 1, Figs 1 A, B). The DNA-analysis (for details, see Väli et al. 2010a) confirmed that the bird is an F1 hybrid between the two species. Field observations indicated that his father had been A. pomarina, his mother A. clanga. The latter was also confirmed by DNA-analysis of feathers collected at the nest. Two years later, a moulted feather of the male A. pomarina was found at the same nest site and sharing of alleles at all studied loci suggested that this bird had sired nestling R7400 in 1999.

Figure 1.

Hybrid spotted eagle R7400 as a nestling on 20 July 1999 (A–B), and as an adult on 28 July 2009 (C–F).

f01_235.eps

Ten years later, on 28 July 2009, hybrid R7400 was caught close to his nest, 9.4 km away from his natal site, where he was breeding with a female A. pomarina. Some of his morphological characters, such as overall dark colour, single prominent carpal crescent and large bill resembled those of A. clanga. Other characters, such as rather short and narrow wings, and banded rectrices, would have suggested A. pomarina. Some characters, such as a yellow-brown iris (which, however, looked dark from a distance) and medium length of the notch on the 4th primary, were intermediate (Table 1, Figs 1 C–H). Surprisingly, several immature characters (see Forsman 1999) had been retained: some fresh medium upperwing-coverts had whitish tips, there were yellowish spots on the back and light edges to some of the feathers on the breast and on the belly (forming spots from a distance), the undertail coverts had whitish tips and bars which together formed a pale area, the secondaries were contrastingly barred and the fresh nape feathers had rufous tips. The bird also showed white edges on the greater underwing coverts, a character pronounced in juveniles and immatures (forming spots), but also present in adult spotted eagles (Forsman 1999, Ü. Väli & A. Nurmla, unpubl. data). At the same time, the bird had several simultaneously ongoing moult waves of remiges (primaries P and secondaries S, numbered respectively descendantly and ascendantly): fresh P2, P4, P5, P7, P8, S2, S3, S6, S7, S8, S10, S12 on the left wing, and fresh P2, P4, P5, P7, P9, S2, S3, S6, S7, S9, S11 on the right wing), suggesting an advanced age of the bird.

Table 1.

Morphological characteristics of the spotted eagle R7400 (F1 hybrid between A. clanga and A. pomarina) in 1999 (nestling, 20 July) and in 2009 (adult, 28 July), and his two offspring (backcrosses between F1 hybrid and A. pomarina) in 2006 (25 July) and 2009 (15 July). All birds were described by the author.

t01_235.gif

The offspring of R7400 (a backcross F1 × A. pomarina; Table 1, Appendix 1) was ringed and studied on 15 July 2009. The nestling had several characters of A. pomarina, such as overall brown coloration in upper-parts, large ochre nape patch (albeit larger than in most A. pomarina nestlings), dark rectrices with light bands to the tip, as well as several characters of A. clanga, such as large bill (relative to wing length), narrow bands on secondaries and very large spots on medium coverts, which were much more prominent than shown by its father in his nestling stage. Its light-coloured breast was also more typical of A. clanga, although it may occur in some A. pomarina as well (Forsman 1999). Probably, R7400 had been present already in 2006, since a ringed adult male spotted eagle with identical field characters was then breeding at the same nest with a female A. pomarina and the genotype of the nestling in 2006 suggested R7400 having been the probable father. The 2006-nestling was very similar in appearance to the chick in 2009, although the rufous areas in its plumage (underbody nape, spots on coverts) were much larger, and its bill was smaller (Table 1, Appendix 1).

Discussion

Earlier records of birds with intermediate or mixed characters (Forsman 1999, Lõhmus & Väli 2001 and references therein, Gutiérrez & Villa 2002, Dombrovski 2005, Treinys 2005) all suggested the viability of hybrid spotted eagles. Moreover, breeding of such birds (Dombrovski 2005, Treinys 2005, Ü. Väli unpubl. data) indicates hybrids to be potentially fertile. Although intermediate appearences can sometimes be explained by morphological variation, which is very large in both species (Forsman 1999), recent genetic studies have confirmed that at least some hybrids are fertile, as backcrossing and introgression of genes from one species to another have been recorded (Väli & Lõhmus 2004, Helbig et al. 2005, Väli et al. 2010b). As far as I know, this is the first case when the hybrid origin of an adult has been confirmed by a ringing record.

Surprisingly, I found several immature characters in the ten-year-old adult bird. According to Forsman (1999: 325, 340), spotted eagles are supposed to attain adult plumage in their fourth or fifth calendar-year, although subadult plumages may then still persist. However, data backing up this opinion are scarce. In A. pomarina, breeding of a four-year-old male with retained juvenile plumage characters has been recorded, whereas — on the other hand — a four-year-old female and a five-year-old female had already attained full adult plumage (Meyburg et al. 2005a). Therefore, Meyburg et al. (2005a) suspected that males attain adult plumage one year later than females, in the fifth year. The data presented here indicate that spotted eagles could retain immature characters until much later, perhaps even close to the average age of an adult spotted eagle (c. 11 years; Meyburg et al. 2005a). Meyburg et al. (1997) reported the breeding of an A. clanga in partial juvenile plumage, but the actual age of the bird was not known. Hybrid origin has been suspected to affect the development of adult plumage characters in spotted eagles (Dombrovski 2005), but it does not necessarily have to since immature characters could be retained throughout life also in other long-lived species that do not hybridise (e.g. Common Gull Larus canus (Olsen & Larsson 2003: 73, K. Rattiste & L. Saks, unpubl. data). Whatever the reason, proper ageing of eagles in the field is difficult; hence, some records of birds breeding at an unusually young age might be erroneous if not confirmed with other data, such as ringing or repeated DNA-analysis.

The hatching and breeding site of R7400 were very close to one another. This is not surprising, as eagles are known for their philopatry (Ferrer 1993, Wood 2009). However, in A. pomarina previously recorded distances between hatching and nesting sites varied between 0.13 and 550 km (Danko & Maderic 2008). At the nest level, the hatching site can be considered as intermediate but the nesting site was typical of A. pomarina — a patch of old-growth spruce forest (Appendix 2). At the landscape level, both sites closely resembled the habitat of A. clanga in Estonia, with large water bodies surrounded by wetland nearby. This is in concordance with other nest sites of mixed pairs in Estonia and supports the idea that mixed pairs have settled in former territories of A. clanga (Lõhmus & Väli 2005), and that hybridisation is an intermediate step in the extinction process of A. clanga populations (Väli et al. 2010b). Indeed, this region of east-central Estonia has been known for formerly harbouring several pairs of A. clanga while only one mixed pair (mother of R7400 still breeding with a male A. pomarina) and the backcrossing pair described in this paper have remained today. Moreover, the current breeding territory of R7400 was earlier occupied by an A. clanga pair in 1997–2001 (nesting only 200 m, 340 m and 820 m from the R7400 nest) and by an A. clanga × A. pomarina pair in 1993–1994 (nest site 1510 m away) and in 2002–2004 (340 m away).

I thank Urmas Abel, Asko Lõhmus and Ain Nurmla for their help in the field, and Ugis Bergmanis, Valery Dombrovski and Rimgaudas Treinys for fruitful discussions on field characters of spotted eagles. Rob G. Bijlsma, Valery Dombrovski, Rimgaudas Treinys and two anonymous referees gave valuable comments on a first draft of the manuscript. Fieldwork and genetic analyses were financed by the Estonian Science Foundation projects ETF6050 and ETF7593.

References

1.

K. Baker 1993. Identification guide to European non-passerines. BTO Guide 24. BTO, Thetford. Google Scholar

2.

U. Bergmanis 1989. How to identify the Spotted Eagle Aquila clanga Pallas and the Lesser Spotted Eagle Aquila pomarina C. L. Brehm. Putni Dabā 2: 113–122. Google Scholar

3.

U. Bergmanis 1996. On the taxonomy of the Lesser Spotted Eagle Aquila pomarina and the Greater Spotted Eagle A. clanga. In: B.-U. Meyburg & R. D. Chancellor (eds), Eagle Studies. WWGBP, Berlin, London & Paris, pp. 115–117. Google Scholar

4.

U. Bergmanis , A. Petrinš , M. Strazds , I. Krams 1997. Possible case of hybridization of the Lesser Spotted Eagle and the Greater Spotted Eagle in Eastern Latvia. Putni Dabā 6.3: 2–6. Google Scholar

5.

U. Bergmanis & M. Strazds 2001. Another possible hybridization case of Lesser and Greater Spotted Eagle in Latvia. Putni Dabā 11.2: 6–7. Google Scholar

6.

Š. Danko & B. Maderič 2008. Nesting of the Lesser Spotted Eagle (Aquila pomarina) at its hatching site. Slovak Raptor Journal 2: 77–80. Google Scholar

7.

V. Dombrovski 2005. Hybridation entre Aigles criard Aquila clanga et pomarin A. pomarina en Biélorussie: conséquence taxonomique. Nos Oiseaux 52: 27–30. Google Scholar

8.

C. Dombrovski V. 2006. Morphological characteristics and diagnostic features of the Greater Spotted (Aquila clanga), Lesser Spotted (A. pomarina) Eagles, and their hybrids. Ornitologia 33: 29–41. Google Scholar

9.

M. Ferrer 1993. Juvenile dispersal behaviour and natal philopatry of a long-lived raptor, the Spanish Imperial Eagle Aquila adalberti. Ibis 135: 132–138. Google Scholar

10.

D. Forsman 1999. The raptors of Europe and the Middle East : a handbook of field identification. Poyser, London. Google Scholar

11.

R. Griffiths , M.C. Double , K. Orr & R.J.G. Dawson 1998. A DNA test to sex most birds. Mol. Ecol. 7: 1071–1075. Google Scholar

12.

R. Gutiérrez & S. Villa 2002. A possible hybrid Spotted Eagle × Lesser Spotted Eagle in Spain. Birding World 15: 104–105. Google Scholar

13.

J. Helbig A. , I. Seibold , A. Kocum , D. Liebers , J. Irwin , U. Bergmanis , B.-U. Meyburg , W. Scheller , M. Stubbe & S. Bensch 2005. Genetic differentiation and hybridization between Greater and Lesser Spotted Eagles (Accipitriformes: Aquila clanga, A. pomarina). J. Ornithol. 146: 226–234. Google Scholar

14.

A. Lõhmus & Ü. Väli 2001. Interbreeding of the Greater Aquila clanga and Lesser Spotted Eagle A. pomarina. Acta ornithoecol. 4: 377–384. Google Scholar

15.

A. Lõhmus & Ü. Väli 2004. The effects of habitat quality and female size on the productivity of the lesser spotted eagle Aquila pomarina in the light of the alternative prey hypothesis. J. Avian Biol. 35: 455–464. Google Scholar

16.

A. Lõhmus & Ü. Väli 2005. Habitat use by the vulnerable Greater Spotted Eagle Aquila clanga, interbreeding with the Lesser Spotted Eagle Aquila pomarina in Estonia. Oryx 39: 170–177. Google Scholar

17.

B.-U. Meyburg , T. Mizera , G. Maciorowksi & J. Kowalski 1997. Schelladler Aquila clanga brütet in partiellem Jugendgefieder. Limicola 11: 82–87. Google Scholar

18.

B.-U. Meyburg , T. Belka , S. Danko , J. Wójciak , G. Heise , T. Blohm & H. Matthes 2005a. Geschlechtsreife, Ansiedlungsentfernung, Alter und Todesursachen beim Schreiadler Aquila pomarina. Limicola 19: 153–179. Google Scholar

19.

B.-U. Meyburg , T. Mizera , J. Matthes , K. Graszynski , J.P. Schwanbeck & G. Maciorowski 2005b. Hybridisation of Greater Aquila clanga and Lesser Spotted Eagle A. pomarina in Poland and Germany. In: T. Mizera & B.-U. Meyburg (eds), International Meeting on Spotted Eagles (Aquila clanga, A. pomarina and A. hastata) — Research and Conservation. Biebrza National Park, Osowiec, pp. 115–117. Google Scholar

20.

P. Mirski 2009. Selection of nesting and foraging habitat by the Lesser Spotted Eagle Aquila pomarina (Brehm) in the Knyszyńska forest (NE Poland). Polish J. Ecol. 57: 581–587. Google Scholar

21.

J.-P. Schwanbeck 2008. Die erste und erfolgreiche Hybridisation zwischen dem Schrei- und Schelladler (Aquila pomarina und clanga) in Deutschland im Land Mecklenburg-Vorpommern. Acta ornithoecol. 6.2: 123–130. Google Scholar

22.

R. Treinys 2004. Important landscape factors for the breeding territory selection by Lesser Spotted Eagle (Aquila pomarina). Acta Zoologica Lituanica 14: 58–61. Google Scholar

23.

R. Treinys 2005. The Greater Spotted Eagle Aquila clanga: previous, current status and hybridisation in Lithuania. Acta Zoologica Lituanica 15: 31–38. Google Scholar

24.

Ü. Väli 2004. Sex ratio of Lesser Spotted Eagle Aquila pomarina nestlings in good and poor breeding years. Bird Study 51: 189–191. Google Scholar

25.

Ü. Väli & A. Löhmus 2004. Nestling characteristics and identification of the Lesser Spotted Eagle Aquila pomarina, Greater Spotted Eagle A. clanga, and their hybrids. J. Ornithol. 145: 256–263. Google Scholar

26.

U. Väli , R. Treinys & A. Löhmus 2004. Geographical variation in macrohabitat use and preferences of the Lesser Spotted Eagle Aquila pomarina. Ibis 146: 661–671. Google Scholar

27.

Ü. Väli , P. Saag , V. Dombrovski , B.-U. Meyburg , G. Maciorowski , T. Mizera , R. Treinys & S. Fagerberg 2010a. Microsatellites and single nucleotide polymorphisms in avian hybrid identification: a comparative case study. J. Avian Biol. 41: 34–49. Google Scholar

28.

U. Väli , V. Dombrovski , R. Treinys , U. Bergmanis , S. J. Daroczi , M. Dravecky , V. Ivanovski , J. Lontkowski , C. Maciorowski , B.-U. Meyburg , T. Mizera , R. Zeitz , H. Ellegren 2010b. Widespread hybridization between the Greater Spotted Eagle Aquila clanga and the Lesser Spotted Eagle A. pomarina (Aves: Accipitriformes) in Europe. Biol. J. Linn. Soc. 100: 725–736. Google Scholar

29.

P.B. Wood 2009. Recovery distances of nestling Bald Eagles banded in Florida and implications for natal dispersal and philopatry. J. Raptor Res. 43: 127–133. Google Scholar

Appendices

Samenvatting

Hybridisatie tussen Schreeuwarend Aquila pomarina en Bastaardarend A. clanga komt in Europa veel voor. Er is echter weinig bekend over de vruchtbaarheid van de daaruit voortvloeiende nakomelingen. Hier wordt een vogel beschreven die in 2009 bij zijn nest in Estland werd gevangen en als nestjong in 1999 bleek te zijn geringd. Hij was gepaard met een Schreeuwarend, en was vermoedelijk dezelfde vogel die in 2006 op hetzelfde nest een jong had grootgebracht met een Schreeuwarend als partner. De gevangen vogel had een Schreeuwarend als vader en een Bastaardarend als moeder, iets wat uit zowel veldkenmerken als DNA-analyse naar voren kwam. Hoewel dit mannetje inmiddels tien jaar oud was, bevatte zijn verenkleed nog tal van kenmerken van een onvolwassen vogel. Dit verklaart misschien de meldingen van arenden broedend op een ongebruikelijk jonge leeftijd: de kans is groot dat dit volwassen hybride vogels zijn geweest met veerpartijen die deden denken aan die van een onvolwassen vogel (iets wat onder hybriden vaker voorkomt dan bij zuivere vogels). De beide jongen van dit mannetje hadden kenmerken van zowel Schreeuw- als Bastaardarend. Hij is het levende bewijs dat — althans sommige — hybriden van Schreeuw- en Bastaardarenden vruchtbaar zijn. Het mannetje broedde op slechts 9,4 km van zijn geboorteplaats. De nestplaats in een opstand oude Fijnspar Picea abies was kenmerkend voor Schreeuwarend, maar op landschapsschaal was de broedplaats typisch voor Bastaardarend: moerassen met grote waterpartijen. In Estland worden deze bastaardarendhabitats in toenemende mate door mengparen in gebruik genomen. Hybridisatie zou dan een tussenstap kunnen zijn in het uitstervingsproces van de lokale populatie Bastaardarenden. (RGB)

Appendix 1

Appendix 1.

Offspring of R7400 (backcrosses between F1 hybrid male and A. pomarina female) on 25 July 2006 (A–C) and on 15 July 2009 (D–E).

fA01_235.eps

Appendix 2

Appendix 2.

Nest site characteristics of the hybrid spotted eagle R7400.

tA01_235.gif
Ülo Väli "Successful Breeding of a Ten-Year-Old Hybrid Spotted Eagle Aquila clanga × A. pomarina Retaining Immature Plumage Characters," Ardea 98(2), 235-241, (1 October 2010). https://doi.org/10.5253/078.098.0214
Received: 16 December 2009; Accepted: 12 May 2010; Published: 1 October 2010
JOURNAL ARTICLE
7 PAGES


SHARE
ARTICLE IMPACT
Back to Top