Ann. Zool. Fennici 50: 333–346 ISSN 0003-455X (print), ISSN 1797-2450 (online) Helsinki 18 December 2013 © Finnish Zoological and Botanical Publishing Board 2013 Factors affecting the goldcrest/firecrest abundance ratio in their area of sympatry Jelena Kralj1,*, Jirí Flousek2, Miljenko Huzak3, Davor Ćiković1 & Zdravko Dolenec4 1) Institute of Ornithology, Croatian Academy of Sciences and Arts, Gundulićeva 24, HR-10000 Zagreb, Croatia (*corresponding author’s e-mail: [email protected]) 2) Krkonose National Park Administration, Dobrovskeho 3, CZ-54301 Vrchlabí, Czech Republic 3) Department of Mathematics, Faculty of Science, University of Zagreb, Bijenička cesta 30, HR-10000 Zagreb, Croatia 4) Department of Zoology, Faculty of Science, University of Zagreb, Rooseveltov trg 6, HR-10000 Zagreb, Croatia Received 19 Nov. 2012, final version received 2 Feb. 2013, accepted 30 May 2013 Kralj, J., Flousek, J., Huzak, M., Ćiković, D. & Dolenec, Z. 2013: Factors affecting the goldcrest/ firecrest abundance ratio in their area of sympatry. — Ann. Zool. Fennici 50: 333–346. The goldcrest (Regulus regulus) and the firecrest (Regulus ignicapilla) are sympatric over a large part of Europe, but with different abundance ratios. We studied the effects of geographical location, vicinity of the species range boundaries, habitat and climate factors on the goldcrest/firecrest abundance ratio. At the continental scale, a weighted multiple linear regression model resulted in four significant covariates: temperature, precipitation, forest type and occurrence rate (representing the vicinity of the species’ range boundaries). The firecrest dominates in warmer and more humid areas and its dominance is more pronounced in mixed forests. The projection of the model showed that in any combination of temperature, precipitation and occurrence rate, the prob- ability to encounter the goldcrest is higher in coniferous forests. Studies in Croatia and the Czech Republic showed regional differences in habitat preferences related to forest type. A significant effect of the seasonal dynamics of precipitation was confirmed in Croatia. Climate change and changes in forestry may influence the distribution and abundance of these two Regulus species in Europe. Introduction cies may differ in their (micro)habitat or diet requirements or in the time when they utilize The coexistence of species is possible only if the available resources at the highest rate. Dif- their niches (sensu Hutchinson 1957) are not ferences in food sources or foraging techniques identical. A group of closely related or simi- are often reported among sympatric congeneric lar species must differ among themselves suf- avian species (Dyrcz & Flinks 2003, Navarro ficiently to ensure that each obtains an adequate et al. 2009). Interspecific competition for food share of the resources it needs (Pielou 1974). resources among sympatric species is known Niche segregation may have diverse forms: spe- to result in the divergence of species morphol- 334 Kralj et al. • ANN. ZOOL. FeNNIcI Vol. 50 ogy (Reifová et al. 2011). Trophic segregation nistic and courtship behaviours serve as isolating is most often related to adaptations in body size mechanisms, while isolation through vocalisa- and bill, leg or wing morphology (James 1982, tion appears to be of minor importance (Thaler Reifová et al. 2011). Studies on the relative den- 1986, del Hoyo et al. 2006). sities of sympatric congeneric avian species may Both the goldcrest and firecrest inhabit mixed help in understanding the effects of climate and and coniferous forests, but their habitats differ habitat factors on bird populations (Järvinen & across the continent. Glutz and Bauer (1991) Väisänen 1979). found a strong association of the goldcrest with Two of the six species of the family Regulidae coniferous trees, while Becker (1977) found no are widespread across Europe and are sympatric differences in the species’ main habitat require- over a large part of the continent. The goldcrest ments. The external morphology and foraging (Regulus regulus) belongs to the Palearctic faunal behaviour of the goldcrest support its preference type with an extensive but discontinuous distribu- for spruce (Leisler & Thaler 1982). Goldcrest tion from western Europe to Japan. Its European habitats are dominated by Norway spruce and breeding area largely overlaps with that of the silver fir (Abies alba), while pines, except the Norway spruce (Picea abies), extending between mountain pine (Pinus uncinata), are generally the July isotherms of 14–23 °C and up to 2200 m avoided (del Hoyo et al. 2006). The study of a.s.l. The fire crest (Regulus ignicapilla) belongs forest bird trends in Europe showed a positive to the Holarctic faunal type and is confined to correlation between winter weather (winter tem- southwestern and central Europe and northern perature anomaly) and the goldcrest population Africa (Baker 1997). The breeding range of the trend in Europe (Gregory et al. 2007). Habitat firecrest in Europe extends between the July iso- choice of the firecrest is broader and it accepts therms of 16–24 °C and is usually found below even a small admixture of spruce, fir or pine in 1000 m a.s.l. (del Hoyo et al. 2006). The north- deciduous forests as a suitable nesting habitat easterly distributed goldcrest and southwesterly (Hagemeijer & Blair 1997). It also breeds in distributed firecrest coexist across a large area of deciduous forests, showing a preference for oak sympatry in central Europe. The two species often (del Hoyo et al. 2006). The firecrest’s pref- have overlapping territories, and there is no evi- erence for pines was noted in some parts of dence of interspecific territoriality (Fouarge 1974, Europe (Archaux & Bakkaus 2007, Ukmar et al. Leisler & Thaler 1982). However, hybridization 2007), but not in others (Wesołovski et al. 2002, occurs on rare occasions (Cobb 1976, Thorpe Nikolov 2007), while Becker (1977) suggested 1983, Jennings 1985). the avoidance of pine forests by both species. For sympatric sibling species, coexistence in Towards its southern limit, the firecrest becomes the same habitat is associated with two main eco- more typical in montane forests (Leisler & logical processes: competition and interbreeding. Thaler 1982, Hagemeijer & Blair 1997); it also The goldcrest and firecrest reduce competition occupies more humid habitats (Glutz & Bauer through differences in their feeding ecology. The 1991). diet of both species consists almost exclusively In forest stands where the two Regulus spe- of arthropods, but the goldcrest specialises on cies coexist, one often dominates, sometimes smaller prey than the firecrest. They have also with more than ten times higher densities evolved different foraging behaviours: goldcrests (Bodenstein 1985, Saniga 1995). Despite the more often cling vertically and hang, especially number of studies in different forest areas of along undersides of dense branches, whereas Europe, there is currently a lack of research on firecrests also forage in less dense branches, factors affecting the ratio of the two Regulus often standing (Leisler & Thaler 1982, Thaler species at regional and broader scales. Moreover, & Thaler 1982). Interbreeding is prevented by ecological studies from different areas showed ethological barriers of readily distinguishable differences in habitat preferences of each spe- behavioural patterns. It has been shown that in cies. By studying the abundance ratio of the two these two Regulus species, differences in antago- species which is not affected by local differences ANN. ZOOL. FeNNIcI Vol. 50 • Factors affecting goldcrest/firecrest abundance ratios 335 in absolute abundances caused by a number of Methods factors, such as habitat quality, patchiness, unfa- vourable weather conditions etc., the patterns of Continental scale dominance of one species over the other can be uncovered. It also enables the use of heterogene- The data used in the analysis at the continental ous published data and the analysis at a larger scale included our own bird censuses and infor- spatial scale. The differences in relative densities mation obtained from the literature, totalling 63 of other congeneric forest passerines (Parus and samples from 26 sites. We obtained published Fringilla) have been attributed to differences data from the zone of sympatry, covering the in habitats and, to some extent, climate factors area between 41°N and 53°N, and 3°W and 24°E (Järvinen & Väisänen 1979). The combination of (Table 1 and Fig. 1). We used only data based on climate change and changes in forestry, resulting standard methodology (point count, line transect in the spread of coniferous and especially pine and mapping methods) dated from the end of the forests, may influence the distribution and abun- 1970s onwards (i.e. obtained within the last ca. dance of forest birds in Europe. To understand 30 years), with densities given for the two Regu- such changes, it is necessary to improve our lus species. We considered only investigations knowledge of habitat requirements of those birds in coniferous and mixed forests (including plots on wider scale. of deciduous forests with admixture of conifer- We propose that the ratio of the two Regulus ous trees, that fulfilled other assumptions), and species must be a result of different factors: geo- excluded those where the two Regulus species graphical location and occurrence patterns across were present at very low densities (density of the continent (with dominance of the goldcrest in the dominant species