Coexistence of protected avian predators: does a recovering population of White- tailed Eagle threaten to exclude other avian predators? Rimgaudas Treinys, Deivis Dementavičius, Gintautas Mozgeris, Saulis Skuja, Saulius Rumbutis & Darius Stončius European Journal of Wildlife Research ISSN 1612-4642 Volume 57 Number 6 Eur J Wildl Res (2011) 57:1165-1174 DOI 10.1007/s10344-011-0529-7 1 23 Your article is protected by copyright and all rights are held exclusively by Springer- Verlag. This e-offprint is for personal use only and shall not be self-archived in electronic repositories. If you wish to self-archive your work, please use the accepted author’s version for posting to your own website or your institution’s repository. You may further deposit the accepted author’s version on a funder’s repository at a funder’s request, provided it is not made publicly available until 12 months after publication. 1 23 Author's personal copy Eur J Wildl Res (2011) 57:1165–1174 DOI 10.1007/s10344-011-0529-7 ORIGINAL PAPER Coexistence of protected avian predators: does a recovering population of White-tailed Eagle threaten to exclude other avian predators? Rimgaudas Treinys & Deivis Dementavičius & Gintautas Mozgeris & Saulis Skuja & Saulius Rumbutis & Darius Stončius Received: 17 December 2009 /Revised: 11 March 2011 /Accepted: 14 March 2011 /Published online: 7 April 2011 # Springer-Verlag 2011 Abstract The processes of competition and predation high. In this study, we investigated nesting habitat overlap determine the degree to which species can coexist; the between internationally protected diurnal tree-nesting avian importance of competition in particular has been empha- predators of central Europe, namely, White-tailed Eagle sized at high trophic levels. Competition exclusion will (Haliaeetus albicilla), Lesser Spotted Eagle (Aquila occur when habitat overlap between sympatric species is pomarina), Black Stork (Ciconia nigra), and Osprey (Pandion haliaetus). We found significantly different nesting habitats among the study species and suggest that Communicated by C. Gortázar this could be a consequence of the resource-based segrega- R. Treinys (*) tion, but not a consequence of asymmetrical interspecific Nature Research Centre, competition. The results also show that habitat of the Akademijos 2, recovering populations of White-tailed Eagle overlapped 08412 Vilnius, Lithuania with the habitat used by the Lesser Spotted Eagle, Black e-mail: [email protected] Stork, and Osprey to varying extents with a niche overlap : D. Dementavičius S. Rumbutis values being below the competition exclusion threshold. The Foundation for the Development of Nature Protection Nevertheless, we suggest that competition by White-tailed Projects, Eagle at a population level may limit Osprey, though not Savanorių pr. 173, 03150 Vilnius, Lithuania Lesser Spotted Eagle or Black Stork. : D. Dementavičius S. Rumbutis Keywords Habitat . Overlap . Avian predator . Department of Ornithology, T. Ivanauskas Zoological Museum, Coexistence . Conservation Laisvės al. 106, 44253 Kaunas, Lithuania G. Mozgeris Introduction GIS Education and Research Centre, Institute of Environment, Lithuanian University of Agriculture, Studentų 13, Ecological differences among species that lead to niche 53362 Kaunas Distr., Lithuania partitioning and therefore coexistence can occur because (1) different species may specialize in distinct resources S. Skuja (classical resource partitioning); (2) different species may Department of Silviculture, Lithuanian University of Agriculture, Studentų 11, Akademija, be limited by the same resources or natural enemies, but Kaunas Distr. 533621, Lithuania differ in terms of when they exploit the resource or respond to natural enemies (temporal niche partitioning); and (3) č D. Ston ius species could differ in terms of where they experience, and Lithuanian Fund for Nature, Algirdo 22-3, respond to, limiting factors (spatial niche partitioning; Vilnius 03218, Lithuania Amarasekare 2003). The processes of competition and Author's personal copy 1166 Eur J Wildl Res (2011) 57:1165–1174 predation determine the degree to which species can coexist al. 2001; Skuja and Budrys 1999;Struwe-Juhl2000; (Martin 1988), with predation being considered to have at Šablevičius 2001; Treinys et al. 2009). least a similar or even greater effect on animal communities The White-tailed Eagle (body mass, ∼3.1–6.9 kg) is than competition (Krüger 2002b; Suhonen et al. 2007). largely a resident raptor species occupying territories most Although the role and relative importance of factors of the year (Dementavičius and Treinys 2009). Populations shaping species' interaction and communities has been the in the countries around the Baltic Sea decreased rapidly in subject of hot controversy (Krüger 2002b), competition the 1960s and 1970s, but wide-range protective measures importance has been emphasized at high trophic levels yielded positive results, and the population of the species (Hakkarainen et al. 2004). increased substantially between 1970 and 1990 (Helander Coexistence can be thought of as resulting from and Stjernberg 2003; Stjernberg et al. 2005). Following a competing species exhibiting differences along four major continued population increase across Europe during 1990– niche axes: resources, natural enemies, space, and time 2000, the European breeding population currently com- (Amarasekare 2003). In the community of sympatric prises 5,000–6,600 pairs (BirdLife International 2004). The diurnal raptors, however, differences along the resources first breeding pairs in Lithuania were found in 1987, and axis could play a most important role: food abundance latest figures suggest the breeding population to be ∼90 along with the availability of suitable nest sites has been pairs (Dementavičius 2007). White-tailed Eagles prey considered the most important resource in raptors (Newton mainly on fish and waterfowl (Cramp and Simmons 2003). Sympatric raptors usually consume different prey 1980), but is known to kill other raptors (Dementavičius (Giovanni et al. 2007; Olsen et al. 2010), but intense 2004; Helander 1983; Mikkola 1983). The Lesser Spotted competition for nest sites could occur among forest- Eagle is a migratory species with a body mass of ∼1.1– dwelling raptors (Krüger 2002a), which typically prefer 2.2 kg (Cramp and Simmons 1980). Its European popula- old growth forests at different spatial scales (Treinys and tion (14,000–19,000 pairs) is declining (BirdLife Interna- Mozgeris 2010 and references therein). Heavy stick nests of tional 2004), as is the Lithuanian population (Treinys et al. medium-size and large raptors can only be constructed in 2007), which comprises 1,931–2,869 pairs (Mischenko et large trees (Kostrzewa 1996; Lõhmus 2006), and this al. in press). It preys mainly upon small mammals, although demand greatly reduces the potential nesting habitat. certain species of amphibians are also common in its diet Timber harvesting reduces the availability of suitable (Meyburg et al. 2001). The Black Stork is a migratory nesting structures for raptors in managed forests (Lõhmus species with a body mass of ∼2.4–3.2 kg (Janssen et al. 2003). Consequently, a lack of suitable forest patches could 2004). Between 7,800 and 12,000 pairs breed in Europe increase competition for available nest sites (Hakkarainen et (BirdLife International 2004), where the recent trends are al. 2004). During the last two decades, differences between geographically distinct: range expansion and population nesting habitat of sympatric diurnal forest-dwelling raptors increases dominate in the west, while declines are reported mostly analyzed the species system of Northern Goshawk in the east (Janssen et al. 2004). The Lithuanian population Accipiter gentilis, Common Buzzard Buteo buteo,and has declined and currently comprises 650–950 pairs Honey Buzzard Pernis apivorus (Kostrzewa 1996; Gamauf (Treinys et al. 2008). It feeds on fish and amphibians (del 2001; Krüger 2002a; Hakkarainen et al. 2004), but other Hoyo et al. 1992). The Osprey is a migratory ichthyoph- species systems are covered as well (Aquila chrysaetos, agous species with a body mass of ∼1.1–2.1 kg (Cramp and Aquila heliaca, and Haliaeetus albicilla (Katzner et al. Simmons 1980). Most European populations were either 2003); Aquila clanga and Aquila pomarina (Lõhmus and stable or increasing between 1990 and 2000, and the Väli 2005); and Aegypius monachus, A. pomarina, European population is now believed to have reached Hieraaetus pennatus, and A. gentilis (Poirazidis et al. 7,600–11,000 breeding pairs (BirdLife International 2004). 2007)). In this study, we attempted to cover a new set of In Lithuania, the population has increased over the last two species and investigated habitat overlap of sympatric decades to ∼50 pairs (Šablevičius 2001). differently sized internationally protected diurnal tree- Carrete et al. (2005) suggested that when habitat overlap nesting avian predators of central Europe: White-tailed is slight, interspecific competition seems to be a secondary Eagle H. albicilla, Lesser Spotted Eagle A. pomarina, factor in the population decline of a subdominant raptor Black Stork Ciconia nigra, and Osprey Pandion haliaetus. species. The population increase of the largest species in an All these species are long lived, exhibit a high degree of avian predator community may present a special conserva- site-fidelity, have large home-ranges, avoid vicinity of tion dilemma when the dominant and the subdominant humans, prefer to