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© 2018 Academia Sinica, Taiwan Open Access Weather Conditions Influence Egg Volume Repeatability in Clutches of the Red-backed Shrike Lanius collurio Artur Golawski1 and Cezary Mitrus2,* 1University of Natural Sciences and Humanities in Siedlce, Faculty of Natural Science, Department of Zoology, Prusa 12, 08-110 Siedlce, Poland, E-mail: artur[email protected] 2Department of Zoology, University of Rzeszów, Zelwerowicza 4, 35-601 Rzeszów, Poland (Received 6 December 2016; Accepted 29 December 2017; Published 25 January 2018; Communicated by Chih-Ming Hung) Citation: Golawski A, Mitrus C. 2018. Weather conditions influence egg volume repeatability in clutches of the Red-backed Shrike Lanius collurio. Zool Stud 57:2. doi:10.6620/ZS.2018.57-02. Artur Golawski and Cezary Mitrus (2018) Birds show considerable variation in egg size, both within and between clutches. There are many factors affecting egg dimensions including features of the birds themselves, territory quality, food abundance and weather conditions. One feature that varies in clutches is repeatability of egg dimensions within a clutch. We studied variation in egg size in clutches of the Red-backed Shrike Lanius collurio in east-central Poland and examined the effects of territory quality and weather conditions on egg size repeatability. Repeatability of egg size was low and ranged from 0.51 to 0.55. No significant differences in egg dimensions were found between clutch size classes (3 to 7 eggs, modal clutch size of 6). Weather conditions only influenced repeatability of egg volume. This parameter was affected by the year and one environmental factor - total rainfall immediately before egg laying. With increasing rainfall, the repeatability of egg volume decreased. Weather conditions can influence food availability and in this way also affect egg size. The Redbacked Shrike diet consists mainly of insects, the activity of which significantly decreased during rainfall. In such conditions, birds have to spend more energy to gain food, which could consequently lead to differences in egg size. Key words: Egg dimensions, Farmland, Repeatability, Rainfall, Territory quality, Weather. *Correspondence: Tel: +48177855459. E-mail: [email protected] BACKGROUND Birds show considerable variation in egg size within a clutch and it is known that egg size can influence the reproductive output of birds, especially by affecting the growth (Järvinen and Ylimaunu 1986) or survival rates of nestlings (Williams 1994). For many birds - including Passerines - daily nutrient intake affects egg production (Perrins 1996; Ward and Bryant 2006). As a consequence, nutrient availability is likely to set a constraint on egg size by influencing the process of egg formation (Martin 1987). Environmental stress on individuals can also influence egg size, e.g. changes in food availability (Bańbura and Zieliński 1998; Christians 2002). Evidence also exists that animals have been affected by weather conditions and recent climate change (Tryjanowski et al. 2002; Parmesan and Yohe 2003; Root et al. 2003). These affects have led to changes in population sizes and densities and their distributions, timing of migration and changes in breeding performance - including egg size (Crick 2004; Walther et al. 2017). One major concern is that climate change will lead to more extreme weather events (Easterling et al. 2000) and have a significant influence on the breeding biology of birds, including, for example, an increase Zoological Studies 57: 2 (2018) doi:10.6620/ZS.2018.57-02 1 © 2018 Academia Sinica, Taiwan in egg size variation within clutches. In addition to variation in weather conditions, territory structure and quality can strongly affect food abundance (Golawski and Meissner 2008) and thus also environmental stress on individuals. It has been shown that territory quality can significantly influence egg size (Parker and Begon 1986; Bańbura et al. 2010), such that a higher food availability was related to reduced variation in egg volume (Takagi 2003). Recently, substantial changes in farmlands - including the disappearance of marginal habitats rich in biodiversity - have been observed (Büchs 2003; Brambilla et al. 2010); this has the potential to also negatively affect birds (Evans 2004; Tryjanowski et al. 2011; Morelli 2013). As a consequence, it is expected that birds’ egg sizes differ between habitats with different food supplies (Chabi et al. 2000; Bourgault et al. 2007). These two factors - weather conditions and territory quality - can influence environmental stress on individuals and thus on egg size. A relatively easy way to effectively evaluate the impact of environmental conditions on egg dimensions is to estimate repeatability of egg parameters in clutches (Bańbura and Zieliński 1990; Falconer and Mackay 1995). Variation in egg dimensions results from both genetic determination and the impact of environmental conditions. High repeatability suggests that phenotypic variance has a significant heritable component and low repeatability suggests a significant environmental component (Bańbura and Zieliński 1998). The main goal of this study was to examine how susceptible variation in egg dimensions is to environmental influences in female Red-backed Shrikes Lanius collurio breeding in farmland in east-central Poland. We wanted to examine which had the stronger effect on egg size repeatability: territory quality or weather conditions at egg laying time. MATERIALS AND METHODS Study area The study was carried out in east-central Poland, near Siedlce (52°12'N, 22°17'E) from 2000-2002. The study area consisted of 855 ha of extensive agricultural landscape. Arable fields predominated in this area (53.5%), mainly with rye and potato crops. Meadows and pastures covered 21.1% and the proportion of set-asides was 2.2%. Woodlands and apple orchards were also present in addition to these open habitats. Red-backed Shrikes occupied open habitats at the edges of woodlands, orchards or scattered trees and bushes. Bird data The Red-backed Shrike is widespread in Europe with stabilised population estimates ranging from 6,300 to 13,000 million breeding pairs (BirdLife International 2004). Breeding occurs in various habitats, such as woodland edges, forest plantations and orchards. However, the largest numbers of breeding pairs occur in farmland (Cramp and Perrins 1993). The average density of the Red-backed Shrike in the study area in this period was 0.6 pair/10 ha (Goławski 2006). Very low philopatry was observed in the local population (Tryjanowski et al. 2007). We looked for Red-backed Shrike nests between mid-May and the end of July from 20002002, checking all possible locations favorable for nesting. Nests were checked only 2-3 times due to the possibly strong human impact on nest success (Tryjanowski and Kuźniak 1999). We measured eggs only in completed clutches (N = 75) at the end of the incubation period. The maximum length and breadth were measured with sliding calipers to the nearest 0.1mm. All eggs were measured by one person (AG), which eliminated any interobserver variability. We calculated the egg volume index (V) from the length (L) and breadth (B) using the formula re-scaled for Red-backed Shrike: V = 0.5322 × L × B2 (Surmacki et al. 2006). Repeatability of egg size within clutches was calculated as the intra-class correlation coefficient using variance components derived from one-way ANOVA and following Lessells and Boag (1987), by applying the formula: r = (MSA - MSW)/[ MSA + (n0 - 1) MSW], where MSA is the between-clutch mean square, MSW is the within-clutch mean square and n0 is a coefficient related to sample size per group in ANOVA, given by: n0 = 1/(a - 1) * [Σ ni (Σ ni2/ Σni)], where ni is the size in the i-th group and a is the number of groups (Lessells and Boag 1987). Mean values for all egg characteristics in each clutch were used as unit observations throughout this paper to avoid pseudoreplication (Lessells and Boag 1987). Habitat structure in territories The average territory size for this species page 2 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan is 1.5 ha, based on studies of its biology and breeding ecology conducted throughout many countries in Europe (Cramp and Perrins 1993). Thus, the present study utilized this territory size using the method described below and previously used by Golawski and Meissner (2008). Around each nest, a hypothetical territory 70 m in radius was drawn and a circle of 1.54 ha area was obtained. Because the Red-backed Shrike does not use the insides of woodlands, established territories that included woodlands were limited to a 7 m wide strip of the woodland edge (the greatest distance from the woodland edge in which a nest was found). Other habitat components were included in these territories and their radii were enlarged to obtain a territory size equal to 1.54 ha. The territory structures are presented in table 1. Having one person (AG) describe territories guaranteed the same precision in drawing sketches of the territory characteristics. Weather data Weather data were obtained from the website: http://www.tutiempo.net for the nearest meteorological station in Siedlce town (10 km south of the study area). We assumed, after Diehl’s study (1998), that the size of eggs in the clutch might be affected by the weather of the week starting 4 days before the laying date of the first egg. As well as weekly average temperature, total rainfall (in mm) in this period was also taken into account. These two weather factors were used in other papers to ask questions similar to ours (e.g. Górski et al. 2015; Parejo et al. 2015). Statistical analysis We analysed the influence of average temperature, amount of rainfall and structure of habitats in each territory on the repeatability of egg parameters in the Red-backed Shrike. A principal components analysis (PCA) was carried out with habitat variables describing the 75 territories to obtain a reduced number of factors that summarized habitat structure. Only PCs with eigenvalues > 1 were retained. We used generalised linear models to test for the effects of territory habitat structure (four scores of PCA) and weather conditions (average temperature and total rainfall) on the repeatability of egg parameters in the Red-backed Shrike. In single GLM with 7 covariates we included three egg parameters - length, breadth and volume - and did three separate analyses. In the calculation, the year was added as a categorical factor. The rest of the variables were treated as continuous predictors. Values describing egg repeatability matched Gaussian distributions. Variables describing weather data were square root transformed. To test for the presence of a trade-off between egg size and clutch size, we also used GLM (normal distribution of all dependent variables), and in analyses the year was added as a categorical factor and the average temperature and total rainfall as a continuous predictors. The level of statistical significance was set at a = 0.05 in all analyses. We used Statistica 10.0 (StatSoft Table 1. Territory structure and principal components analyses performed with 11 variables defining habitat structure in 75 territories of Red-backed Shrikes. Significant correlations between original variables and components (all P < 0.01) are shown in bold Variable Mean Range PC1 PC2 PC3 PC4 Fences (m) 34.7 0-231 -0.80 -0.23 0.03 0.03 Ditches (m) 49.8 0-282 -0.60 -0.21 0.06 -0.12 Roads (m) 67.7 0-230 0.19 -0.70 0.10 -0.32 Hedges (m) 56.4 0-274 -0.78 -0.42 -0.10 0.03 Meadows (ha) 0.53 0-1.54 -0.52 0.68 0.33 -0.15 Pastures (ha) 0.16 0-1.44 -0.49 -0.25 -0.51 -0.25 Fallows (ha) 0.13 0-1.07 0.15 -0.46 0.43 0.37 Fields (ha) 0.41 0-1.53 0.73 -0.19 -0.22 -0.52 Orchards (ha) 0.21 0-1.54 0.16 -0.13 -0.12 0.86 Settlements (ha) 0.01 0-0.33 0.08 -0.40 0.63 -0.06 Trees (no.) 0.7 0-6 -0.08 0.12 0.71 -0.24 Eigenvalue - - 2.74 1.73 1.52 1.42 % variance accounted for - - 0.25 0.16 0.14 0.13 page 3 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan 2011) software for statistical calculations. RESULTS Red-backed shrike clutches (n = 75) contained 3 to 7 eggs. Mean clutch size was 5.3 ± 0.81 (mean ± SD) and modal clutch size was 6 eggs. The mean egg length was 22.07 ± 0.83 mm, breadth 16.51 ± 0.41 mm and volume 3.21 ± 0.22 cm3. Egg dimensions were similar for all 3 breeding seasons (Table 2). No significant differences in egg dimensions were found between clutch size classes; other variables included in the model were year, mean temperature, and total rainfall no influenced on egg dimensions (GLMegg length = 1.17, p = 0.330; GLMegg breadth = 0.64; p = 0.738; GLMegg volume = 0.95, p = 0.483, respectively). Repeatability estimates were low and ranged from 0.51 to 0.55 (Table 3). The four principal components (PC1PC4) accounted for 68% of the total variation in the habitat structure of territories, with eigenvalues > 1. PC1 accounts for 25% of original variance. Fence and hedge length showed the highest negative correlation with PC1 scores. Meadow area (positive) and road length (negative) provided the major loading on PC2 (16% of original variance). Settlement area and number of single trees showed a positive correlation with PC3 (14% of original variance). And lastly, orchard area showed the highest positive correlation with PC4 score (13% of original variance, Table 1). Generalised linear models of habitat territory structures (PC1-PC4) and weather conditions on the repeatability of egg dimensions showed statistical significance only in the case of egg volume (Table 4). The repeatability of egg volume was affected by year and one environmental factor - total rainfall. The repeatability of egg volume decreased with increasing rainfall, but this relationship was weak. Differences in egg volume repeatability between years were also slight, the highest value was 0.6 (in 2001) and lowest was 0.5 (in 2000). The territories’ habitat structures (for PC1-PC4) did not significantly influence the repeatability of egg dimensions (Table 4). DISCUSSION The mean clutch size of the Red-backed Shrike recorded in this study did not deviate substantially from values found in other European populations (Antczak et al. 2009; Söderström and Karlsson 2011). In this study, we tested the influence of weather conditions and territories’ habitat structure on the diversity of egg dimensions in Red-backed Shrike clutches. Repeatability of egg size could be related to the repeatability of environmental stress on laying females (Bańbura and Zieliński 1998; Christians 2002). Overall, the results indicated that weather was a more important factor than habitat structure in the territories for the repeatability of eggs. Among weather factors, only the rainfall in the period before egg laying significantly influenced the repeatability of egg dimensions (egg volume). We did not find relationships between the repeatability of length or breadth of eggs in the clutch. These Table 2. Egg dimensions (mean ± SD), ambient temperature and total rainfall during the Red-beaked Shrike’s 3 month breeding season Year Egg length (mm) Egg breadth (mm) Egg volume (cm3) Mean daily temperature (°C) Total rainfall (mm) 2000, n = 21 22.07 ± 0.87 16.52 ± 0.39 3.21 ± 0.23 16.1 214.4 2001, n = 29 22.26 ± 0.77 16.60 ± 0.44 3.27 ± 0.20 16.4 167.9 2002, n = 25 21.84 ± 0.84 16.40 ± 0.39 3.13 ± 0.21 18.5 208.8 Table 3. Repeatability values (r) and confidence limits (95% Cl) for egg dimensions in a Red-backed Shrike population, n = 75 clutches. All F-ratios (one-way ANOVA) are significant at P < 0.050 Parameter rF-ratio 95% Cl Length 0.53 2.70 0.48-0.59 Breadth 0.51 4.34 0.46-0.56 Volume 0.55 3.86 0.49-0.60 page 4 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan results indicated that most of the environmental factors studied had no effect on repeatability of egg dimensions in clutches of the Red-backed Shrike in east-central Poland, which is consistent with an earlier study related to clutch size (Golawski 2008). Values of the repeatability of egg size varied between 0.51 and 0.55 and were low compared with other species; for example, values in a study by Christians (2002) were usually higher than 0.68. Within passerines, similarly low values for the repeatability of egg dimensions are uncommon; however, low values have been noted in Bearded Tits Panurus biarmicus (Surmacki et al. 2003) and a small population of Blue Tits Cyanistes caeruleus in Algeria (Chabi et al. 2000). Other studies on Red-backed Shrikes from western Poland showed that repeatability of egg volume in the clutch was 0.7 (Tryjanowski et al. 2004). Our results indicate that in east-central Poland, Red-backed Shrike egg dimensions (egg volume) showed low heritability and were mostly determined by environmental conditions. The results’ statistical significance for only egg volume was related to the fact that volume increases approximately with the cube of the linear measurements of the egg. However, mechanism of egg production and determination of it’s phenotype is not known enough. Similar results were found in the American Pipit Anthus rubescens and Bearded Tits (Hendricks 1991, Surmacki et al. 2003, respectively); both studies showed high variability in egg volume. The largest eggs in a population can be two times larger than the smallest ones. The variation in this parameter is probably due be due to the variance accumulation from the computational formulas, which are calculated in such a manner that they inherently contain cumulated variance from the input variables (Bańbura 1996). Inverterbrate availability - including insects that are food for Red-backed Shrikes (Tryjanowski et al. 2003; Golawski 2006; Morelli et al. 2015) - changes with weather conditions (Cucco and Malacarne 1996; Kuper et al. 2000). Rain and the Table 4. Generalised linear models of habitat territory structure (PC1-PC4) and weather conditions on repeatability of egg dimensions (length, breadth, volume) in Red-backed Shrikes in east-central Poland Predictor Estimate SE Wald statistics p-value Egg length Average temperature 0.34 0.21 2.63 0.105 Sum of rainfall 0.01 0.03 0.15 0.701 PC1 -0.03 0.03 0.62 0.432 PC2 -0.03 0.04 0.49 0.482 PC3 0.01 0.04 0.08 0.779 PC4 -0.01 0.04 0.01 0.923 Year 0.15 0.10 2.21 0.137 Egg breadth Average temperature 0.11 0.20 0.29 0.589 Sum of rainfall 0.04 0.03 2.15 0.140 PC1 0.02 0.03 0.24 0.621 PC2 -0.02 0.04 0.25 0.610 PC3 0.06 0.03 2.86 0.091 PC4 0.06 0.04 2.44 0.118 Year 0.17 0.10 2.55 0.109 Egg volume Average temperature 0.01 0.02 0.01 0.995 Sum of rainfall -0.48 0.19 6.57 0.010 PC1 0.02 0.03 0.58 0.447 PC2 -0.03 0.04 0.73 0.393 PC3 0.03 0.03 0.85 0.357 PC4 0.04 0.04 0.94 0.330 Year 0.30 0.09 10.18 0.001 page 5 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan drop in temperature it leads to cause a distinct decrease in the numbers of insects (Grüebler et al. 2008). Furthermore, a large amount of variation in egg size is dependent on a high-quality diet (Williams 1996), which can also be related to weather conditions. Thus, rainfall and a likely decrease in food availability probably influenced egg volume repeatability in the clutch and the low values of repeatability of egg dimensions and was consistent with results from a study on Bearded Tits (Surmacki et al. 2003). In this species, changes in food abundance in the littoral zone of a lake had a significant influence on the repeatability of egg dimensions. If the food supply for laying females varies across short timescales, it can affect their condition and this can influence mean egg size. Thus, potential environmental stress affects female condition and, consequently, repeatability of egg volume (Tryjanowski et al. 2004). Differences in the repeatability of egg volume within the clutch were also observed in relation to the year of study. The highest value was noted in 2001; the 3 months recorded in 2001 (May-July) had much less rainfall (167.9 mm) than the same months in 2000 and 2001 did (214.4 mm and 208.8 mm respectively, Table 2). As well as variation in rainfall, food abundance may also have an influence on results and may also vary year-byyear (Hill 1985). Habitat structure did not have a significant influence on egg dimension repeatability. Habitat structure within the same sample area did not affect clutch size but did influence the number of fledglings (Golawski and Meissner 2008). Various habitats used by shrikes differed in food abundance (Golawski and Golawska 2008), but weather conditions can have an additional influence on food availability, which may make weather conditions more important (Rodenhouse and Holmes 1992; Tryjanowski et al. 2003). CONCLUSIONS For Red-backed Shrikes in east-central Poland, the weather is a more important factor influencing on repeatability of egg dimensions than territory quality. Consequently, in the event of climate change increasing the incidence of extreme rainfall (Sanz 2002), this factor may influence optimal egg size in the future and have effects on the condition, size and dynamics of Redbacked Shrike populations. Acknowledgments: We thank Shelley Hinsley for providing comments that improved the quality of the manuscript and for correcting the English. We are also grateful to the two anonymous reviewers for their critical remarks regarding the first version of this paper. This study complies with current Polish laws and was financially supported by the Siedlce University of Natural Sciences and Humanities (AG) and the University of Rzeszów (CM). Authors’ contributions: AG and CM performed the field work and written the manuscript. All authors contributed to drafting and revising the manuscript. All authors read and approved the final manuscript. Competing interests: AG and CM declare that they have no conflict of interests regarding the publication of this paper. Availability of data and materials: Data and materials are available in Department of Zoology University of Natural Sciences and Humanities in Siedlce. Consent for publication: Not applicable. Ethics approval consent to participate: This study complies with current Polish laws. REFERENCES Antczak M, Golawski A, Kuźniak S, Tryjanowski P. 2009. Costly replacement - how do different stages of nest failure affect clutch replacement in the red-backed shrikes Lanius collurio? Ethol Ecol Evol 21:127-136. Bańbura J. 1996. Intrapopulation variability of egg measurements in the Barn Swallow Hirundo rustica. Wyd UŁ Łódź. Bańbura J, Zieliński P. 1990. Within-clutch repeatability of egg dimensions in the Black-headed Gull Larus ridibundus. J Orn 131:305-310. Bańbura J, Zieliński P. 1998. An analysis of egg-size repeatability in Barn Swallows Hirundo rustica. Ardeola 45:183-192. Bańbura M, Sulikowska-Drozd A, Kaliński A, Skwarska J, Wawrzyniak J, Kruk A, Zieliński P, Bańbura J. 2010. Egg size variation in Blue Tits Cyanistes caeruleus and Great Tits Parus major in relation to habitat differences in snail abundance. Acta Ornithol 45:121-129. BirdLife International. 2004. Birds in Europe population estimates trends and conservation status. BirdLife International, Cambridge. Bourgault P, Thomas DW, Blondel J, Perret P, Lambrechts MM. 2007. Between-population differences in egg composition in Blue Tits (Cyanistes caeruleus). Can J Zool 85:71-80. Brambilla M, Casale F, Bergero V, Bogliani G, Crovetto RF, Roati M, Negri I. 2010. Glorious past uncertain present page 6 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan bad future? Assessing effects of land-use changes on habitat suitability for a threatened farmland bird species. Biol Conserv 143:2770-2778 Büchs W. 2003. Biodiversity and agri-environmental indicators - general scopes and skills with special reference to the habitat level. Agric Ecosyst Environ 98:35-78. Chabi Y, Benyacoub S, Bańbura J. 2000. Egg-size variation in Algerian populations of the Blue Tit (Parus caeruleus ultramarinus) effects of altitude and habitat. Rev Ecol 55:183-192. Cramp S, Perrins CM. (eds) 1993. Lanius collurio Red-backed Shrike Handbook of the Birds of Europe the Middle East and North Africa. Vol VII, Oxford University Press, New York. Christians JK. 2002. Avian egg size variation within species and inflexibility within individuals. Biol Rev 77:1-26. Crick HQP. 2004. The impact of climate change on birds. Ibis 146:48-56. Cucco M, Malacarne G. 1996. Reproduction of the pallid swift (Apus pallidus) in relation to weather and aerial insect abundance. Ital J Zool 63:247-253. Diehl B. 1998. Reproduction in the Red-backed shrike (Lanius collurio) - a long term study. IBCE Tech Publ 7:39-42. Easterling DR, Meehl GA, Parmesan C, Changnon SA, Karl TR, Mearns LO. 2000. Climate extremes observations modeling and impacts. Science 289:2068-2074. Evans KL. 2004. The potential for interactions between predation and habitat change to cause population declines of farmland birds. Ibis 146:1-13 Falconer DS, Mackay TFC. 1995. Introduction to Quantitative Genetics. Longmann, London. Golawski A. 2006. Comparison of methods for diet analysis and prey preference a case study on the Red-backed Shrike Lanius collurio. Ornis Fennica 83:108-116. Golawski A. 2008. No evidence of weather effect found on the clutch size eggs sizes and their hatchability in the redbacked shrike Lanius collurio in eastern Poland. Ann Zool Fenn 45:513-520. Golawski A, Golawska S. 2008. Habitat preference in territories of the Red-backed Shrike Lanius collurio and their food richness in an extensive agriculture landscape. Acta Zool Acad Sci Hung 54:89-97. Golawski A, Meissner W. 2008. The influence of territory characteristics and food supply on the breeding performance of the Red-backed Shrike (Lanius collurio) in an extensively farmed region of eastern Poland. Ecol Res 23:347-353. Górski A, Nowakowski JJ, Bańbura J. 2015. Variation in eggsize traits of the European Roller (Coracias garrulus) in eastern Poland. Ornis Fenn 92:213-220. Grüebler MU, Morand M, Naef-Daenzer B. 2008. A predictive model of the density of airborne insects in agricultural environments. Agric Ecosyst Environ 123:75-80. Hendricks P. 1991. Repeatability of size and shape of American Pipit eggs. Can J Zool 69:2624-2628. Hill DA. 1985. The feeding ecology and survival of pheasant chicks on arable farmland. J Appl Ecol 22:645-654. Järvinen A, Ylimaunu J. 1986. Intra clutch egg-size variation in birds physiological responses of individuals to fluctuations in environmental conditions. Auk 103:235-237. Kuper J, Van Duinen G-J, Nijssen M, Geertsma M, Esselink H. 2000. Is the decline of the Red-backed Shrike (Lanius collurio) in the Dutch coastal dune area caused by a decrease in insect diversity? Ring 22:11-25. Martin TE. 1987. Food as a limit on breeding birds. A life-history perspective. Annu Rev Ecol Syst 18:453-487. Lessells CM, Boag PT. 1987. Unrepeatable repeatabilities a common mistake. Auk 104:116-121. Morelli F. 2013. Relative importance of marginal vegetation (shrubs, hedgerows, isolated trees) surrogate of HNV farmland for bird species distribution in Central Italy. Ecol Engine 57:261-266. Morelli F, Bussiere R, Golawski A, Tryjanowski P, Yosef R. 2015. Saving the best for last Differential usage of impaled prey by red-backed shrike (Lanius collurio) during the breeding season. Behav Proces 119:6-13. Parejo D, Aviles JM, Exposito M. 2015. Hatching asynchrony and spring climatic conditions in the European Roller. Evol Biol 42:443-451. Parker GA, Begon M. 1986. Optimal size and clutch size effects of environment and maternal phenotype. Am Nat 128:573592. Parmesan C, Yohe G. 2003. A globally coherent fingerprint of climate change impacts across natural systems. Nature 421:37-42. Perrins CM. 1996. Eggs egg formation and the timing of breeding. Ibis 138:2-15. Rodenhouse NL, Holmes RT. 1992. Results of experimental and natural food reductions for breeding black-throated blue warblers. Ecology 73:357-372. Root TL, Price JT, Hall KR, Schneider SH, Rosenzweig C, Pounds AJ. 2003. Fingerprints of global warming on wild animals and plants. Nature 421:57-60. Sanz JJ. 2002. Climate change and birds have their ecological consequences already been detected in the Mediterranean Region? Ardeola 49:109-120. Söderström B, Karlsson H. 2011. Increased reproductive performance of Red-backed Shrikes Lanius collurio in forest clear-cuts. J Ornithol 152:313-318. StatSoftInc. 2011. Statistica data analysis software system. http://www.statsoft.com. Accessed 20 Feb. 2016. Surmacki A, Kuczyński L, Tryjanowski P. 2006. Eggshell pattering in the Red-backed Shrike Lanius collurio relation to egg size and potential function. Acta Ornithol 41:145151. Surmacki A, Stępniewski J, Zduniak P. 2003. Repeatability of egg dimensions within the clutches of Bearded Tit Panurus biarmicus. Acta Ornithol 38:123-127. Takagi M. 2003. Seasonal change in egg-volume variation within a clutch in the Bull-headed Shrike Lanius bucephalus. Can J Zool 81:287-293. Tryjanowski P, Golawski A, Kuzniak S, Mokwa T, Antczak M. 2007. Disperse or stay? Exceptionally high breeding-site infidelity in the Red-backed Shrike Lanius collurio. Ardea 95:316-320. Tryjanowski P, Hartel T, Báldi A, Szymański P, Tobolka M, Herzon I, Golawski A, Konvička M, Hromada M, Jerzak L, Kujawa K, Lenda M, Orłowski G, Panek M, Skórka P, Sparks TH, Tworek S, Wuczyński A, Żmihorski M. 2011. Conservation of farmland birds faces different challenges in Western and Central-Eastern Europe. Acta Ornithol 46:1-12. Tryjanowski P, Karg MK, Karg J. 2003. Diet composition and prey choice by the red-backed shrike Lanius collurio in western Poland. Belg J Zool 133:157-162. Tryjanowski P, Kuźniak S. 1999. Effect of research activity on the success of Red-backed shrike Lanius collurio nests. Ornis Fenn 76:41-43. page 7 of 8Zoological Studies 57: 2 (2018) © 2018 Academia Sinica, Taiwan Tryjanowski P, Kuźniak S, Sparks T. 2002. Earlier arrival of some farmland migrants in western Poland. Ibis 144:6268. Tryjanowski P, Sparks TH, Kuczyński L, Kuźniak S. 2004. Should avian egg size increase as a result of global warming? A case study using the red-backed shrike (Lanius collurio). J Ornithol 145:264-268. Walther BA, Ren-Jen CJ, Lin H-S, Sun Y-H. 2017. The effects of rainfall, temperature, and wind on a community of montane birds in Shei-Pa National Park, Taiwan. Zool Stud 56:23 doi:10.6620/ZS.2017.56-23. Ward S, Bryant DM. 2006. Barn swallows Hirundo rustica form eggs mainly from current food intake. J Avian Biol 37:179189. Williams TD. 1994. Intraspecific variation in egg size and egg composition in birds effects on offspring fitness. Biol Rev 68:35-59. Williams TD. 1996. Variation in reproductive effort in female Zebra Finches (Taeniopygia guttata) in relation to nutrientspecific dietary supplements during egg laying. Physiol Zool 69:1255-1275. page 8 of 8Zoological Studies 57: 2 (2018)