NORTH-WESTERN JOURNAL OF ZOOLOGY 10 (1): 101-109 ©NwjZ, Oradea, Romania, 2014 Article No.: 131803 http://biozoojournals.ro/nwjz/index.html
Assessing the effects of environmental factors on the presence and density of three shrike species in a continental and a coastal area of central Greece
Athanassios I. SFOUGARIS*, Sofia G. PLEXIDA and Alexandra D. SOLOMOU
Laboratory of Ecosystem and Biodiversity Management, Department of Agriculture, Crop Production and Rural Environment, University of Thessaly, Fytokou str., Ν. Ionia, 384 46 Volos, Greece. E-mail’s: [email protected]; [email protected]; [email protected] *Corresponding author, A.I. Sfougaris, Tel / Fax: +30 2421093274, E-mail: [email protected]
Received: 20. January 2013 / Accepted: 09. July 2013 / Available online: 26. December 2013 / Printed: June 2014
Abstract. This study was conducted in two different Mediterranean areas of central Greece and aimed at (i) comparing the breeding density and frequency of occurrence of shrike species between these two areas, (ii) identifying the key characteristics of habitats for each species, and (iii) evaluating possible underlying environmental factors determining the shrike’s presence. To assess which factors mostly affect density, estimated with the point count method, we used the non-parametric test Kruskal - Wallis, Spearman's correlation coefficient, Canonical Analysis and Canonical Correspondence Analysis (CCA). Environmental variables tested were microclimate (air temperature and humidity), vegetation (herbaceous cover, shrub cover and shrub height), topography (altitude, slope, road presence, distance from nearest road, settlement and river) and habitat type (broad leaf forest, agricultural land, rangeland and abandoned olive groves). Between the two areas types, only Lanius senator mean breeding density was significantly different. The CCA model was significant (p < 0.05). Our results highlighted that L. minor did not occupy plots of agricultural land (cereals) and was negatively related to the distance of the nearest road. L. senator did not occupy plots of broad leaf forest and was positively related to the existence of the nearest road. Furthermore, the species exhibited the habit of perching along roadsides. On the contrary, L. collurio was characterized as habitat generalist in landscapes of central Greece.
Key words: Lanius collurio, Lanius senator, Lanius minor, Mediterranean landscapes, Canonical Correspondence Analysis.
Introduction & Bota 2003, Giralt & Valera 2007). On a local geographical scale, bird species of The occurrence of animal and plant species in ag- the same taxonomic group are often separated by ricultural landscapes is the result of geomor- habitat. In Greece, altitude has also differentiated phological, climatic and biotic factors of the land- the distribution of Lanius species. L. senator occurs scape and intensity of land use (Sotherton et al. mainly on coastal plains and low foothills, up to 1998, Burel et al. 1998). Several studies have sug- 500 m above sea level, but occasionally up to 1,000 gested that migrant bird species, such as Lanius m a. s. l. L. minor typical breeding habitat is open sp., might be more sensitive to habitat changes areas with cereal fields, meadows or dry stony and their populations decline is more severe than grassland with patches of bushes and trees. It oc- resident species one (Sol et al. 2005). curs from sea level up to 1,000 m and occasionally Species of the Laniidae family are species of higher (Handrinos & Akriotis 1997). L. collurio conservation concern for Europe (SPEC) and are breeds mainly in altitudes ranging from 500 to associated with traditional farmlands and the 1,500 m, but sometimes up to 1,700 m (Handrinos semi-natural habitats (Tucker & Evans 1997, For- & Akriotis 1997). L. collurio is distributed to mostly nasari et al. 1997). Lanius collurio has declined over farmed landscapes characterised by a matrix of the last 50 years in many parts of its European fields and grasslands, where marginal features range. Despite the fact that the L. senator has a such as hedgerows, shrubs and small trees, are in- large decline throughout its breeding range in terspersed (Goławski & Meissner 2008, Brambilla Europe, few studies have been dedicated on its et al. 2009). Although L. collurio requires special breeding ecology (Bechet et al. 1998, Isenman & landscape characteristics, including abundant food Fradet 1998, Harris & Franklin 2000, Nikolov and diverse land use patterns (Söderström 1999), 2005). In addition, studies from southern France its presence in an environment does not necessar- and northeast Spain have detected a decline of L. ily imply a high quality environment. minor populations during the last decades (Giralt L. minor occupies a variety of open habitat 102 A.I. Sfougaris et al. systems ranging from vineyards and fallows in (Magnesia Prefecture; see Fig. 1). Continental area is France (Isenmann & Debout 2000), short-grass characterized by a mixed farmland – woodland and is steppes in Hungary (Lovászi et al. 2000), mead- part of the Special Protected Area “Mountain Antichasia – Meteora”, considered a very important site for its avi- ows, orchards and bare ground in Slovakia (Wir- fauna (Meliadis et al. 2009). It lies into Quercetalia pubes- titsch et al. 2001) to cereal and pasture in Italy centis zone of the Mediterranean-type vegetation and ex- (Guerrieri et al. 1995) and cereal, sparse shrub land tends in altitudes between 800 and 1,130 m a.s.l. The for- and fallows in Spain (Giralt & Bota 2003). The ested area of the site (65%) consists of Quercus pubescens, wide variety of occupied habitats associated with Q. frainetto and Q. cerris stands. Other woody vegetation specific land-use patterns suggests that certain ag- (25%) includes Q. coccifera, Carpinus orientalis, Pyrus amyg- ricultural practice , presence of certain plant spe- daliformis and Cotinus coggygria. The rest 10% of the site is covered by cultivations, mainly cereals, and urban areas. cies and key vegetation features (coverage of bare The presence of hedgerows among the fields is rather re- ground/herbaceous/shrub) are among the main stricted. The climate is characterized as typical sub- determinants of the distribution of L. minor (Wir- Mediterranean, with relatively cold winters and warm titsch et al. 2001). Mediterranean ecosystems are and dry summers, with mean annual air temperature known to host one of the richest flora and fauna in 16.8oC, mean annual air humidity 65.9% and mean annual the world. These ecosystems are characterized as precipitation 750 mm. Average minimum temperature of o global biodiversity ‘‘hotspots’’ (Myers et al. 2000) the coldest months in 2009 was 2.5 C, whereas maximum means of the warmest months was 32.5 °C (Hellenic Me- and appear to be especially susceptible to the im- teorological Service 2009). pacts of global climate change (Lavorel et al. 1998, Peñnuelas et al. 2002). A great number of studies have shown that climatic conditions influence ar- rival dates, timing of breeding and population size in migrating birds (Sæther et al. 2004, Gordo 2007, Newton 2007). Inclement weather (cool and rainy season) is considered as the main cause for L. sena- tor breeding failures in central Europe (Schön 1994). Although there are a number of descriptive studies from the Mediterranean basin on the breeding habitat of the three species (Brahimia et al. 2003, Tsakiris et al. 2009, Brambilla et al. 2010), few of them have focused on linking shrike den- sity, climate and habitat. Even though SE Europe hosts an important part of the European shrike populations (BirdLife International 2004), most of Figure 1. Map of the study area. the relevant studies have been carried out in cen- tral or northern Europe (Roos & Pärt 2004, Tryja- The coastal area is agricultural landscape dominated nowski et al. 2006, Titeux et al. 2007, Goławski & by olive groves (55% of the site area) with admixture of Golawska 2008, Hušek et al. 2009, Pasinelli et al. abandonded olive groves (10%) and is part of the Site of 2011). The general aim of this study was to evalu- Community Importance, “Elos Sourpis-Kouri Almyrou” ate how the density of three Lanius species (L. col- (www.minenv.gr). It falls into the Quercetalia ilicis vegeta- lurio, L. minor, L. senator) is related to climate, to- tion zone, at altitudes up to 230 m a.s.l. The rest of the pography and habitat type in two different Medi- area (35%) is covered by shrubs, such as Olea europaea var. terranean landscapes, one continental and one sylvestris, Quercus coccifera, Arbutus unedo, Pistacia lentiscus and Rubus fruticosus. The climate of the site is typical coastal. We further investigated which habitats are Mediterranean with dry and warm summers and mild occupied by each species and evaluated selected winters, mean annual air temperature 18.7 oC, mean an- environmental factors in determining presence of nual air humidity 66% and mean annual precipitation 580 each species in the habitat. mm. Average minimum temperature of the coldest months in 2009 was 9.75 oC, whereas maximum means of the warmest months was 27.05 °C (Hellenic Meteorologi- Material and methods cal Service 2009).
Study area Bird sampling The study was conducted in two areas of central Greece, Bird surveys were conducted during the breeding season one continental (Trikala Prefecture) and one coastal of 2009 when birds are easily detectable due to territorial Effects of environmental factors on the presence and density of three shrike species 103 displays and nesting activities. The point counts were rangeland, meaning either grassland or shrubland (Pa- surveyed once, but simultaneously at both landscapes, panastasis & Noitsakis 1992), depending on the dominant during 10 April – 15 June. We counted all the individuals cover percentage of the different land use typologies. of the three shrike species seen or heard using the point count method within 50 m radius at 75 point locations in Data analysis each landscape, 150 in total (Bibby et al. 1992). Points Non-parametric tests were used to confirm non-normal were randomly selected and placed at a distance of at distribution of data. All the analyses were carried out on least 200 m between each other and from field limits in the average number of breeding pairs per 0.785ha. Fre- order to avoid double counting and edge effects (Ralph et quency of occurrence of each species was calculated for al. 2005). Each count lasted for 10 min and took place dur- both areas and each category of habitat type. Initially, ing the period of maximum bird activity, from dawn to mean breeding densities and frequencies of occurrence four hours after sunrise in dry weather conditions with were compared between the two areas (continental vs. no wind (Bibby et al. 1992). Counts were made by two ob- coastal) by using the Kruskal-Wallis (KW) and the Mann- servers simultaneously to avoid bias. While not all bird Whitney tests with Bonferroni correction (MW) (Potvin species gender differences are easily visible, it is an easy and Roff 1993, Zar 1999). To test occupancy of different task for an ornithologist to determine which birds are habitat types we used Wilcoxon Signed Rank Test. Spear- male or female by either phenology such as pattern of man’s rank correlation was calculated for all environ- wings or behavior depending of ageing, especially during mental variables to examine correlation with Lanius spe- the breeding season. In addition, as a territorial species cies density. All analyses were performed by IBM SPSS which defends its breeding and foraging habitat, the male for Windows, v. 19.0 (IBM, 2010). and female of the same pair is easily distinguished. Den- To assess which environmental factors determine sity was expressed as breeding pairs per hectare. shrike breeding density, we used the Canonical Corre- As a further step in the analysis, we tested for spatial spondence Analysis (CCA) (75 point locations in each autocorrelation by calculating Global Moran’s I values area, 150 in total) applied in CANOCO (ter Braak & Šmi- (Moran 1950) using the spatial statistics tool for that pur- lauer 2002). The length of the gradients of Detrended Cor- pose in ArcMap (ESRI 2011). The statistical significance of respondence Analysis (DCA) indicated a heterogeneous Moran’s I (p < 0.05) is based on distances by randomiza- dataset (Leps & Šmilauer 2005). The matrix of the species tion (using a Monte Carlo procedure; 200 permutations). presence/absence crossed with the 150 count points was Spatial autocorrelation is the property of having a non- used as input for the DCA and CCA. Abiotic and land- random distribution: it is common in nature as environ- scape variables were transformed into dummy variables mental variables are frequently clustered or spread over using Monte Carlo Permutation Procedure (999 permuta- gradients (Legendre 1993). Although spatial autocorrela- tions). CCA method ordinates species and samples in a tion likely presents a problem for any correlation-based way that the ordination axes represent the maximum study relating ecological condition to surrounding land variability attributable to the environmental parameters. cover, it is rarely measured (King et al. 2005). Relative effects of individual environmental variables are visualized by the relative length of the respective vectors Environmental variables in the ordination space (Salway and Wakefield 2005). Measurements of environmental variables were taken within the same circular plots of 50 m radius where the birds were counted. Within each count point instant air Results temperature and humidity were measured throughout the season using handheld instruments and mean values Breeding density and frequency of occurrence were calculated for both variables. Vegetation variables measured were: percent cover (%) of the herbaceous layer Three shrike species (L. collurio, L. minor and L. using four cover classes (0-25%, 26-50%, 51-75%, > 75%), senator) were recorded in both areas. Presence and percent cover (%) of the shrubs using three classes (0-20%, coincidence or overlap of sampled sites among the 21-40%, > 40%) and the height of shrubs (Prodon & Le- three species is shown in Table 1. Between the two breton 1981). Shrub height, as a microhabitat variable, areas, only L. senator mean breeding density was was measured because it appeared in previous studies significantly different (Kruskal - Wallis χ2 = 3.89, p that most shrikes avoid nesting in habitats with relatively < 0.04) (Table 2). In continental area, L. collurio high shrub height. Regarding topographic characteristics of the count points, altitude and slope (1= 0-17%, 2= 17- showed higher mean breeding density than L. mi- 34%, 3= 34-51%, 4= 51-68%, 5= 68-85%) were derived us- nor (Wilcoxon test, Z = -2.318, p = 0.018) and L. ing a global positioning system. Road presence and the senator (Wilcoxon test, Z = -2.721, p = 0.007). In the distances from the nearest road, settlement and river were coastal area, there were no significant differences also calculated to better explain the breeding habitat se- (P>0.05) in density among shrike species. Spatial lection of the shrike species. We also noted the general autocorrelation was not present (Moran’s I Index = habitat category of the counting points referred to as: (1) -0.02, Zscore = -0.03, p = 0.97). agricultural (cereals with hedges or sparse trees and ac- tive olive groves), (2) broad-leaved forest (Quercus spp.), Only frequency of occurrence of L. senator dif- (3) abandoned olive groves (at least 12 years old) and (4) fered significantly between areas, (Kruskal – Wal- 104 A.I. Sfougaris et al.
Table 2. Lanius sp. mean breeding densities (breeding pairs/ha, b.p./ha) and frequencies of occurrence at the two sampled areas. Statistically significant differences are shown at significance level α = 0.05 (*).
Number of Area types Lanius collurio Lanius minor Lanius senator census points Mean breeding density (SD) Continental 75 0.31 (0.83) 0.10 (0.34) 0.03 (0.20)* Coastal 75 0.18 (0.49) 0.20 (0.58) 0.16 (0.52)* Frequency of occurrence (%) Continental 75 14.66 8.00 2.66** Coastal 75 13.33 16.00 10.66**
Table 1. Presence and coincidence or overlap of sampled Influence of environmental variables sites among the three studied bird species. on shrike’s density
Presence Coincidence (%) L. collurio density was poor correlated with shrub Species Total only (%) LC LS LM cover (rs = 0.21, p < 0.01), whereas L. senator den-
LC 150 19.33 ¯ 2.66 3.33 sity with slope (rs = 0.15, p < 0.01) and altitude (rs = LS 150 8 2.66 ¯ 0.66 -0.20, p < 0.01). LM 150 13.33 3.33 0.66 ¯ Canonical Correspondence Analysis (CCA)
was successfully performed (p < 0.05) (Table 3). CCA-biplot ordination diagrams of bird species and environmental variables are shown in the Fig. 3. The results of CCA showed that axis 1 ac- counted for 23.0% of the total variance among spe- cies and was correlated with distance from nearest river (DFR), road existence (EOR) and type (RT), slope (SL) and altitude (ALT). Canonical axis 2 ac- counted for 17.4% of the total variance and was correlated with the distance from nearest road (DNR) and shrub presence (SP). The most impor- tant parameters which determined the ordination of the areas and species studied were the distance
Figure 2. Frequency of occurrence of each from nearest river and road existence, while the shrike species for the four habitat types. least important were the humidity and habitat type. Specifically, L. collurio density was positively
Table 3. Results of Canonical Correspondence Analysis correlated with the cover of herbaceous plants and among the shrike species and the environmental factors. air temperature, whereas L. minor density was Summary of eigenvalues, species-environmental corre- negatively correlated with the air temperature and lations and % Lanius density variance. positively with the distance from nearest road.
Total Last, L. senator density was positively correlated Axes 1 2 inertia with the road existence and negatively with the al- Eigenvalues 0.23 0.17 0.53 titude and cover of shrubs. Species-environment correlations 0.53 0.45 Cumulative percentage variance
of species data 23.00 40.00 Discussion of species-environment relation 57.15 100.0 Sum of all eigenvalues 0.53 Sum of all canonical eigenvalues 0.13 Continental - coastal landscape comparison Our findings showed that L. collurio was the most abundant among the three species in terms of lis χ2 =3.56, p = 0.05) (Table 2). L. collurio was re- mean breeding density in the study area and par- corded in all types of habitat, whereas L. minor ticularly in the continental area. L. collurio breeds and L. senator were not recorded in broad leaf for- throughout most of Europe, except for the north- est and agricultural habitats, respectively (Fig. 2). ern areas, central and southern Iberia and many
Effects of environmental factors on the presence and density of three shrike species 105
Figure 3. Canonical Correspondence Analysis based on bird species occur- rence in the study area. Arrow lines: en- vironmental variables. The relative length of arrows corresponds to the rela- tive influence of explanatory variables on the dispersion of species in the ordi- nation space. Abbreviations: DNR (dis- tance from nearest road), DFO (distance from settlement), SL (slope), HUM (hu- midity), RT (road type), DFR (distance from river), EOR (existence of road), ATEM (air temperature), CHP (cover of herbaceous plants), HS (height of shrubs), HAB (habitat), ALT (altitude), CS (cover of shrubs), SPA (presence of shrubs).
Mediterranean islands (Battern et al. 1990). The Regardless of the altitude threshold, the sampled mosaic structure of the hilly and mountainous forest is rather closed without any fragments of area (> 800 m) of our continental study site, in- bare ground or orchard trees in their surround- cluding farmland elements, seems to be a favor- ings. able habitat. In addition, at this traditional land- L. minor in our study area occurred in all habi- scape small farms with low pesticide use still tat types except agricultural land, where mainly dominate and high habitat heterogeneity resulting cereals were planted (Fig. 2). Possibly, L. minor in a high diversity of microhabitats. Search for prefers habitats with low vegetation for better ac- similar studies have resulted in other red-backed cessibility to large insects, on which it feeds shrikes reports which showed a clear positive ef- (Krištín 1995). Rangeland was the most often oc- fect of landscape heterogeneity on the bird popu- cupied habitat (Fig. 2). Similar habitat occupancy lations (Goławski 2006, Goławski & Goławska patterns by the same coexisting shrike species 2008). Our data set highlights that L. senator was were detected in central Italy by Guerreri et al. present at coastal area but not in continental one. (1995) where the shrikes were segregating mainly On the contrary, the two other shrike species by vegetation characteristics. According to Mul- demonstrated ecological flexibility in habitat oc- larney et al. (2009) L. minor prefers habitats such as cupancy, which is in accordance to a relevant crops and groves in warm lowland areas at alti- study from central Italy (Morelli 2012). tudes from the sea level to 1,000 m., and L. sena- tor occurs in maquis ecosystems and orchards. Habitat occupancy Possibly, the availability of food and high quality Our results highlighted that L. minor was not pre- perching points are important factors determining sent in agriculture count points and L. senator did landscape occupancy by the species. In another not occupy broad leaf forested count points, area of Greece (Alexandroupolis) three shrike spe- whereas L. collurio is characterized as habitat gen- cies coexist (L. collurio, L. minor, L. senator), but a eralist (Tucker and Evans 1997). In our study area high overlap of sampled sites between L. senator L. collurio was found in all habitat types at both ar- and L. collurio (Moskát & Fuisz 2002). eas. L. senator mainly occurred in farmland and The coexistence of the three shrike species in rangelands. Similar results have presented by rangeland could be explained firstly by the exis- Mullarney et al. (2009). Our results suggest that tence of extensive livestock. Secondly, the fact that forested areas at higher elevations with Quercus rangelands are abandoned and not managed may sp. trees do not provide suitable breeding habitats explain their high occupancy by shrikes. Although for L. senator. This may be explained by the fact a general tendency for a higher beta-diversity of that broad leaf forest count points occurred at an early-successional bird communities in agricul- altitude higher than 850 m in the continental area. tural areas is found compared to woodland habi- 106 A.I. Sfougaris et al. tats in Europe (Blondel & Farre 1988, Paquet et al. (2005) showed that this species prefers warm envi- 2006), in this study this tendency was absent. The ronments with trees for their nesting and feeding effect of human presence was proven to affect the habitats. Also, this study highlighted that L. sena- presence of L. senator and L. minor in the study tor was positively related to the distance of the area. Furthermore, the presence of anthropogenic nearest road. The species exhibited the habit of structures, such as settlements, farming buildings perching along roadsides and flies low to the in the farmland and rural roads increase the gen- ground. Not in Europe, as far as is known, but in eral landscape heterogeneity and probably explain Canada (Miller 1931, Cadman 1986) the same habit the minimization of predation pressure upon was also found for the species Lanius ludovicianus. shrikes (Roos 2002, Roos & Pärt 2004, Morelli et al. It might be mentioned that only 5% of the count 2012). points was less than 200 m from the road. Habitat occupancy of each species was found Environmental variables and shrikes presence to be associated with different vegetation variables The continental area is located at higher elevations (shrubs or cover of herbaceous vegetation). The and therefore its mean air temperatures and hu- most important vegetation variables for L. collurio midity are lower than those of the coastal area. seem to be the presence and the height of shrubs, The climate of both areas is characterized as sub- hence the availability of open herbaceous areas for humid Mediterranean, but it is more severe and foraging (e.g., grasslands or pastures). Intermixing with more dry days in the coastal area (Mavroma- of these components in a mosaic is consistently tis 1980). Canonical Correspondence Analysis in- important to shrike species which tend to nest at dicated that L. collurio density increased with the the edge of patches rather than in the middle of increase of air temperature. Moreover, weather heavily wooded areas (Keinath & Schneider 2005). conditions play an important role in predicting the L. minor density in our study area was negatively activity of L. collurio (Hornman et al. 1998, Kuper correlated with herbaceous plant cover and posi- et al. 2000). Weather affects breeding success be- tively correlated with shrub cover. This finding is cause it changes the availability of insect prey, in agreement with results of other studies (Guerri- mainly Coleoptera, Hymenoptera and Orthoptera, eri et al. 1995, Moskat & Fuisz 2002). Also, high and to a lesser extent of vertebrates (Siikamäki shrub cover that does not allow sufficient light 1996, Tryjanowski et al. 2003). If temperature penetration may, therefore, decrease understory changes at different rates, the synchrony between vegetation cover, which in turn may not provide birds and food supply may become distorted (Vis- more nest-sites and food sources for birds (Quine ser & Both 2005). We found that increased tem- et al. 2007). Another highlight of the present study perature affects increased L. collurio density. Some is that only L. minor density was positively corre- relevant studies have shown that high tempera- lated to the distance from nearest river. Although ture during the breeding season led to increase of we found scarce literature data for other Mediter- L. collurio populations in Belgium (Jacob 1999), in ranean area with which we could compare this France (Kowalski 1999) and in Netherlands (Van finding, in Romania the nest density and habitat Dijk & Hustings 1999). On the contrary, studies in use by L. minor in the river bed of Târnava Mare Hungary (Lovaszi et al. 2000) and Poland (Go- was studied, where the smallest distance from the ławski 2006) have found a negative correlation be- river was 150 m (Moga et al. 2010). tween the temperature and the presence of L. col- The knowledge of presence and characteristics lurio. According to Roos (2004) and DuRant et al. of occupied breeding habitat are essential for the (2012) air temperature is an important factor af- conservation of a species. Structure characterizing fecting egg brooding behavior in birds. Hence, habitat of shrikes can be relevant to a large num- hatching success may be influenced by egg size, ber of species (Tucker & Evans 1997, Pykala 2003, which depends on the weather conditions at the Negri et al. 2005, Brambilla et al. 2008, 2009). Ap- time of laying (Londono et al. 2008, Aslan and Ya- propriate habitat management may allow conser- vuz 2010). Furthermore, annual mean temperature vation of the relatively less frequent L. minor in (17.6oC) and total annual rainfall (51.6 kg/m2) at central Greece. Specifically, key conservation Küçük Menderes Delta form arid periods in Aydin measures should include the maintenance of and its surroundings determining the avifauna shrub cover. 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