(Laniidae) from historical oological collections: interspecific patterns and modest temporal

(Laniidae) from historical oological collections: interspecific patterns and modest temporal | Authorea try { document.documentElement.classList.add('js'); } catch (e) { } var _gaq = _gaq || []; _gaq.push(['_setAccount', 'G-8VDV14Y67G']); _gaq.push(['_trackPageview']); (function() { var ga = document.createElement('script'); ga.type = 'text/javascript'; ga.async = true; ga.src = ('https:' == document.location.protocol ? 'https://ssl' : 'http://www') + '.google-analytics.com/ga.js'; var s = document.getElementsByTagName('script')[0]; s.parentNode.insertBefore(ga, s); })(); Skip to main content Preprints Collections Wiley Open Research IET Open Research Ecological Society of Japan All Collections About About Authorea FAQs Contact Us Quick Search anywhere Search for preprint articles, keywords, etc. Search Search ADVANCED SEARCH SCROLL This is a preprint and has not been peer reviewed. Data may be preliminary. 9 April 2026 V1 Latest version Share on (Laniidae) from historical oological collections: interspecific patterns and modest temporal Authors : Paweł Pstrokoński 0000-0003-2728-2223 , Katarzyna Roguz , Wojciech Wójcik , Martin Päckert 0000-0001-5045-0139 , Joanna Rosenberger 0000-0001-8169-6377 , Dominika Mierzwa-Szymkowiak , Magdalena Sepkowska , Jan Lontkowski , Marek Słupek , Michał Chiliński 0000-0002-3496-9966 , and Damaziak Krzysztof [email protected] Authors Info & Affiliations https://doi.org/10.22541/au.177571480.04282565/v1 246 views 95 downloads Contents Abstract Abstract 1 Introduction 2 Results 3 Discussion 4 Methods Figures Acknowledgements Funding Conflicts of Interest Data Availability Statement Supplementary Material References Information & Authors Metrics & Citations View Options References Figures Tables Media Share Abstract Avian eggs reflect life-history trade-offs, yet shrikes (Laniidae) lack a modern cross-species synthesis of egg morphology. Using historical oological collections spanning 1888–1973, we quantified inter- and intraspecific variation in egg morphology and clutch size in four shrike species: red-backed shrike (Lanius collurio), woodchat shrike (L. senator), lesser grey shrike (L. minor), and great grey shrike (L. excubitor). Clutch size increased over time only in the lesser grey shrike, whereas no robust temporal change was detected in the other species. Where temporal trends in egg morphology occurred, size-related traits generally declined, whereas shape descriptors, including sphericity and shape index, remained comparatively stable. Among species, the great grey shrike laid the largest eggs but the smallest clutches, whereas the red-backed shrike laid the smallest eggs, consistent with a broad size–number trade-off in reproductive allocation. Within species, spatial variation in egg-size traits was evident, particularly in the red-backed shrike and woodchat shrike, whereas evidence for a size–number relationship was weak. Overall, temporal change in shrike reproductive traits was limited and species-specific, while museum collections proved valuable for reconstructing long-term patterns of reproductive variation. Paweł Pstrokoński 1 , Katarzyna Roguz 2 , Wojciech Wójcik 1 , Martin Päckert 3 , Joanna Rosenberger 4 , Dominika Mierzwa-Szymkowiak 5 , Magdalena Sepkowska 6 , Jan Lontkowski 7 , Marek Słupek 8 , Michał Chiliński 9 , Krzysztof Damaziak 1* 1 Department of Animal Breeding, Institute of Animal Sciences, Warsaw University of Life Sciences, Warsaw, Poland 2 Botanic Garden, Faculty of Biology, University of Warsaw, Warsaw, Poland Evolutionary Ecology of Plants, Department of Biology, Evolutionary Ecology of Plants, Marburg University, Marburg, Germany 3 Senckenberg Natural History Collections Dresden, Dresden, Germany 4 Division of Poultry Breeding, Institute of Animal Breeding, Faculty of Biology, Wroclaw University of Environmental and Life Sciences, Wroclaw, Poland 5 Museum and Institute of Zoology, Polish Academy of Sciences, Warsaw, Poland 6 Count Antoni Ostrowski Museum in Tomaszow Mazowiecki, Tomaszow Mazowiecki, Poland 7 Museum of Natural History, Wroclaw University, Wroclaw, Poland 8 Museum of Jacek Malczewski in Radom, Radom, Poland 9 Faculty of Biology, University of Warsaw, Warsaw, Poland *Corresponding author: Krzysztof Damaziak, e-mail: [email protected] (KD) Keywords shrikes (Laniidae), avian egg morphology, clutch size variation, life-history trade-offs, museum collections, macroevolutionary constraints Abstract Avian eggs reflect life-history trade-offs, yet shrikes (Laniidae) lack a modern cross-species synthesis of egg morphology. Using historical oological collections spanning 1888–1973, we quantified inter- and intraspecific variation in egg morphology and clutch size in four shrike species: red-backed shrike ( Lanius collurio ), woodchat shrike ( L. senator ), lesser grey shrike ( L. minor ), and great grey shrike ( L. excubitor ). Clutch size increased over time only in the lesser grey shrike, whereas no robust temporal change was detected in the other species. Where temporal trends in egg morphology occurred, size-related traits generally declined, whereas shape descriptors, including sphericity and shape index, remained comparatively stable. Among species, the great grey shrike laid the largest eggs but the smallest clutches, whereas the red-backed shrike laid the smallest eggs, consistent with a broad size–number trade-off in reproductive allocation. Within species, spatial variation in egg-size traits was evident, particularly in the red-backed shrike and woodchat shrike, whereas evidence for a size–number relationship was weak. Overall, temporal change in shrike reproductive traits was limited and species-specific, while museum collections proved valuable for reconstructing long-term patterns of reproductive variation. 1 Introduction Avian eggs, through their extraordinary diversity in size and shape, provide a unique window into the evolutionary and ecological processes that shape reproductive strategies across bird species. Egg morphology varies markedly across taxa, yet remains constrained by phylogenetic history (Sabri et al. , 1999; Stoddard et al. , 2017). Consequently, eggs can serve as ecological archives, preserving signals of reproductive investment and evolutionary diversification (Hughes, 2015; Damaziak and Marzec, 2022). Egg morphology is also closely tied to species’ life-history strategies, and multiple evolutionary and ecological pressures act on it (Ousterhout, 1980; Rowe, Ludwig and Schluter, 1994; Potti, 2008; Evans et al. , 2009; Padhi et al. , 2013; Shim et al. , 2013; Deeming and Reynolds, 2015; Birkhead et al. , 2019; Ding, Zhu and Zhang, 2023); foremost among these is the trade-off between egg size and clutch size (Blackburn, 1991), whereas species that produce larger clutches often lay smaller eggs, balancing the number of offspring with the resources allocated to each egg (Lack, 1947). Conversely, species with intensive parental care or fewer breeding opportunities may invest more in larger or more energetically costly eggs (Williams, 1994; Christians, 2002). In birds, egg morphology is shaped by both genetic and environmental factors. Assessing whether these reproductive traits vary through time, however, requires datasets spanning many decades. Historical specimens preserved in museum collections provide such material, allowing researchers to reconstruct past phenotypes and assess long-term patterns of variation (Suarez and Tsutsui, 2004; Kemp, 2015; Holmes et al. , 2016; Marini et al. , 2020, 2023). Although preserved specimens do not retain all egg components, they still present value and offer substantial opportunities for long-term, geographic, and comparative analyses of avian reproduction (Suarez and Tsutsui, 2004; Kemp, 2015; Holmes et al. , 2016; Pstrokoński et al. , 2025). Thus, museum egg collections are particularly well suited to investigating broad-scale variation in egg size, shape, and clutch characteristics through time. Although avian reproductive traits may change over time, not all components of reproduction are expected to do so equally. Core life-history traits, such as clutch size and egg size, may be more strongly constrained by phylogenetic history and reproductive strategy than more labile phenological traits (Böhning-Gaese and Oberrath, 1999; Charmantier and Gienapp, 2014). By contrast, phenology-related characteristics, including laying date and migration timing, often show more rapid and plastic responses to environmental change (Charmantier and Gienapp, 2014; Halupka and Halupka, 2017; Romano et al. , 2023). This suggests that long-term temporal change in egg morphology and clutch size may be detectable, but uneven among traits and species, and therefore requires datasets spanning many decades to be evaluated robustly (Suarez and Tsutsui, 2004; Kemp, 2015; Holmes et al. , 2016). We focus on shrikes (Laniidae) because they provide a suitable system for comparative analyses of egg morphology and clutch size. They vary considerably in body size and breeding strategies, ranging from sedentary to long-distance migratory species, while remaining broadly comparable in general breeding ecology as open-habitat passerines. Their eggs are also sufficiently distinctive to allow reliable species-level identification in museum collections, and they differ in both size and shape (Yosef and Zduniak, 2004; Goławski and Mitrus, 2018). Despite shrikes’ broad distribution, a significant knowledge gap remains: a modern cross-species synthesis of shrike egg morphology is lacking. At the same time, recent museum-based work on the red-backed shrike has shown that long-term change in eggshell appearance can be reconstructed over more than a century, underscoring the value of shrikes as a model system for archival studies of egg traits (Sulej et al. , 2025). Previous research on shrike breeding ecology has provided valuable insights into reproductive behaviour and environmental influences, although most studies have focused on single populations or relatively short time frames (typically less than ten years) (Degen et al. , 1992; Bechet, Isenmann and Gaudin, 1998; Hoi et al. , 2004). This leaves unresolved how egg traits and clutch size vary among closely related shrike species and whether such variation is detectable across broader temporal and geographic scales. Here, we examine inter- and intraspecific variation in egg morphology and clutch size in four shrike species that differ in body size and migratory strategy: the red-backed shrike ( Lanius collurio ), woodchat shrike ( L. senator ), lesser grey shrike ( L. minor ), and great grey shrike ( L. excubitor ) (Dunning, 2007) (Figure 1). Using historical oological material collected between 1888 and 1973 from across the species’ breeding ranges, we addressed three questions: (i) do egg size, shape, and clutch size differ among species; (ii) do these traits vary geographically within species; and (iii) is temporal variation in egg morphology and clutch size detectable over the sampling period? We predicted that larger-bodied species would produce larger eggs and smaller clutches, consistent with a size–number trade-off, and that temporal change, if present, would be more evident in size-related traits than in shape-related traits. verbose, tmargin=2.3cm, bmargin=3.4cm, lmargin=1.5cm, rmargin=1.5cm, headheight=1.25cm, footskip=1.25cm \geometryright=1.5cm 00 0.1.0.5em 0.1.1.0.5em BERT Bidirectional Encoder Representations from Transformers CERT/CC Computer Emergency Response Team Coordination Center CVE Common Vulnerabilities and Exposures CTI Cyber Threat Intelligence DARPA Defense Advanced Research Projects Agency EDR Endpoint Detection and Response GAN generative adversarial network GPT Generative pre-Trained Transformer IVAM Investigation, Validation, Active Monitoring LIME Local Interpretable Model-agnostic Explanation MTTR Mean Time to Repair/Respond/Remediate ONNX Open Neural Network Exchange SIEM Security Information and Event Management SOAR Security Orchestration, Automation, and Response TTP tactics, methods and procedure 2 Results 2.1 Among-species comparison We found significant among species differences in egg length and width, with the great grey shrike producing the longest (mean ± SD: 26.4 ± 1.56 mm) and widest eggs (19.3 ± 0.91 mm), while the red-backed shrike produced the shortest (21.9 ± 1.06 mm) and narrowest eggs (16.5 ± 0.55 mm; Table 1, Figure 2; χ² = 946, p < 0.01 and χ² = 1068, p < 0.01, respectively). Similar patterns were observed for egg diameter and volume, with the great grey shrike having the largest diameter (21.4 ± 0.95 mm) and egg volume (5.17 ± 0.71 cm³), and the red-backed shrike the smallest diameter (18.1 ± 0.58 mm) and volume (3.11 ± 0.3 cm³; Table 1, Figure 3C–F; χ² = 1131, p < 0.01 for both traits). Likewise, egg surface area was greatest in the great grey shrike (14.4 ± 1.3 cm²) and smallest in the red-backed shrike (10.3 ± 0.67 cm²; Table 1, Figure 3E; χ² = 1131, p < 0.01). Shell weight did not differ significantly only between the great grey shrike and the lesser grey shrike, with the heaviest shells recorded in the great grey shrike (27.7 ± 3.25 g) and the lightest in the red-backed shrike (17.5 ± 1.83 g; Table 1, Figure 2; χ² = 1086, p < 0.01). The shape index and degree of egg sphericity varied significantly among species (Table 1, Figure 3B, D; χ² = 62.7, p < 0.01 and χ² = 1068, p < 0.01, respectively). While mean clutch size did not differ significantly between the lesser grey shrike and the woodchat shrike, significant differences were observed among the other species (Table 1, Figure 3A; χ² = 130.0, p < 0.01). The largest clutches were recorded in the lesser grey shrike (5.52 ± 1.25 eggs) and the woodchat shrike (5.82 ± 0.84 eggs), while the smallest were in the great grey shrike (4.71 ± 1.26 eggs). 2.2 Within-species comparison A GLMM including species, year, and mean egg volume, with country fitted as a random intercept, indicated a significant positive effect of year on clutch size (β = 0.05, 95% CI: 0.02 to 0.08, p = 0.001; Table 2). Neither species identity nor mean egg volume significantly predicted clutch size (all p ≥ 0.20). Although the coefficient on mean egg volume was negative, consistent with a possible size–number trade-off, the effect was weak and statistically unsupported. Model fit was modest (marginal R² = 0.042; conditional R² = 0.101), indicating that most variation in clutch size remained unexplained by the fixed effects. The random effect of country accounted for a small proportion of the total variance (τ00 = 0.01, ICC = 0.06). Differences in clutch and egg traits among years and countries are presented in Figures S1–S2 and Tables S1–S2. Despite the annual variation in the red-backed shrike clutch size, there was no temporal trend. The linear model estimated a small positive slope (OLS β = 0.01, Figure 4), but the HC3-robust test was not significant ( p = 0.06). Consistent with this, the Theil–Sen trend was not significant ( p = 0.19), and a GAM smooth indicated at most weak nonlinearity (edf = 2.6, p = 0.08). Egg size metrics showed consistent temporal declines. Across all data, egg width, shell weight, diameter, surface area, and volume all decreased over time, with the robust checks concordant for all traits (Kendall’s p ≤ 0.01; Theil–Sen slopes matching OLS; GAM p < 0.01; Figure 4). For the lesser grey shrike, clutch size increased over time (OLS β = 0.03; p < 0.01; HC3 p = 0.01; Figure S3). Robust sensitivity checks corroborated this pattern: (Theil–Sen p = 0.01 and a GAM indicating mild nonlinearity (edf = 2.74, p < 0.01). Kendall’s τ was borderline (τ = 0.28, p = 0.059), so we infer an upward trend with possible gentle curvature. In contrast, the woodchat shrike showed no robust temporal change: the OLS slope was small and borderline (OLS β = 0.01; p = 0.05), became non-significant with HC3 (p = 0.12), Kendall’s (τ = 0.02, p = 0.87) and Theil–Sen (slope = 0, p = 0.12). Although a GAM suggested weak nonlinearity (edf = 2.27, p = 0.04), the inconsistency across diagnostics and discreteness issues argues against a temporal trend. We did not record any temporal trends for the great grey shrike, with all egg size parameters (OLS, HC3-robust regression, Kendall’s τ, and GAM) showing the same results (Figure S1). Egg morphology metrics were strongly intercorrelated: length, width, diameter, surface area, and volume formed a tight block of positive associations (pairwise |ρ| typically ≥ 0.7–0.9). Shape-derived indices (e.g., sphericity, shape index) also correlated with the primary size parameters. Spearman correlations between clutch size and mean egg traits were uniformly small, and none remained significant after Benjamini-Hochberg false discovery rate correction. These results align with the GLMM analyses, which indicate that temporal and geographic factors, rather than single egg metrics, primarily explain variation in clutch size (Figure 4; Figure S1–S4; Table S3). 3 Discussion Using historical egg collections spanning the late nineteenth to mid-twentieth century, we identified temporal and spatial variation in clutch size and egg morphology across four shrike species. Temporal change in clutch size and egg morphology was limited and species-specific rather than general across the studied shrikes. Clutch size increased through time in the lesser grey shrike, whereas evidence for temporal change in the remaining species was weak or inconsistent across robustness checks. Where significant temporal trends in egg morphology were detected, they generally involved declines in size-related traits, most clearly in the red-backed shrike. By contrast, shape-related descriptors remained comparatively stable, suggesting that egg size may be more labile than egg shape in this group. The generally weak and uneven temporal trends suggest that core reproductive traits such as clutch size and egg dimensions may be relatively constrained by phylogeny and life-history strategy (Böhning-Gaese and Oberrath, 1999; Charmantier and Gienapp, 2014). This interpretation is consistent with earlier and recent work on the red-backed shrike, which documented long-term change in egg volume and eggshell appearance, respectively (Tryjanowski et al. , 2004; Sulej et al. , 2025). In contrast, phenology-related traits are often more labile and may respond more rapidly to climatic variability and long-term warming (Charmantier and Gienapp, 2014; Halupka and Halupka, 2017; Romano et al. , 2023). Temporal shifts in egg traits may be subtler and harder to detect, especially in historical datasets with uneven sampling through time (Merilä, Sheldon and Kruuk, 2001; Visser et al. , 2015). Nevertheless, this relative stability can be overridden by strong environmental pressures, such as organochlorine exposure, causing rapid eggshell thinning and spatial variation in calcium availability affecting eggshell structure (Ratcliffe, 1967; Hickey and Anderson, 1968; Newton and Bogan, 1974; Burnett et al. , 2013; Gosler and Wilkin, 2017). Together, these findings suggest that temporal change in shrike egg traits can occur, but it is modest relative to broader interspecific and spatial variation. In addition to temporal patterns, we also found spatial within-species variation in egg-size traits and clutch size, particularly in the two smallest species, the red-backed shrike and the woodchat shrike, whereas egg shape did not vary geographically in any species. This pattern suggests that size-related egg traits may be more responsive to local conditions than shape-related descriptors. Spatial variation in egg size may reflect environmental heterogeneity, including differences in habitat quality or climate (Bańbura et al. , 2018), although the available museum material does not allow these mechanisms to be tested directly. This interpretation is consistent with previous work on the red-backed shrike. No differences in egg dimensions were detected among clutch-size classes, although rainfall before laying influenced within-clutch repeatability of egg volume, suggesting selective rather than uniform environmental effects on egg traits (Goławski and Mitrus, 2018). By contrast, no effects of temperature or rainfall on clutch size, egg volume, within-clutch variation, or hatchability were found in another red-backed shrike population, indicating that weather-related responses may vary among populations or study contexts (Goławski, 2008). The lack of comparable spatial variation in the lesser grey shrike further indicates that these patterns are not uniform across species. More broadly, temporal and spatial variation in egg traits may reflect a combination of population structure, environmental heterogeneity, and reproductive constraints, although the relative importance of these factors cannot be resolved with museum material alone. Among species, the observed differences in egg morphology and clutch size were broadly consistent with body size and reproductive allocation. The great grey shrike, the largest species in the dataset, laid the largest and heaviest eggs but had the smallest clutch size, whereas the red-backed shrike laid the smallest and lightest eggs. This pattern is consistent with a classic interspecific size–number trade-off, in which greater investment per offspring is associated with reduced clutch size (Saether, 1985; Blackburn, 1991; Martin et al. , 2006). The woodchat and lesser grey shrikes, despite producing smaller eggs, had the largest clutches, reinforcing this general pattern. In contrast, within-species associations between clutch size and egg traits were weak, indicating that this trade-off was not strongly supported at the intraspecific level. These findings should be interpreted in light of the limitations of museum oological material. Although historical collections provide access to large numbers of specimens across broad temporal and geographic ranges, they lack information on key reproductive and environmental variables, including female age, breeding conditions, and reproductive success, and they may also reflect collector bias (Thompson and Birkhead, 2020). In addition, the most recent eggs in our material date to 1973, leaving a gap of more than 50 years between the historical dataset and present-day populations. Addressing this gap is challenging as large oological collections were assembled under historical conditions that are no longer replicable under modern legal and ethical standards. Despite these limitations, museum collections remain highly valuable for reconstructing long-term reproductive variation and for providing a historical baseline against which contemporary data can be compared. In summary, historical oological collections revealed clear among-species differences in egg morphology and clutch size, but only limited and uneven temporal change within species. Size-related traits showed greater temporal and spatial variation than shape-related descriptors, while evidence for a within-species size–number relationship was weak. Overall, these results highlight both the value of museum material for comparative studies of avian reproduction and the need for contemporary data to place historical patterns in a modern ecological context. verbose, tmargin=2.3cm, bmargin=3.4cm, lmargin=1.5cm, rmargin=1.5cm, headheight=1.25cm, footskip=1.25cm \geometryright=1.5cm 00 0.1.0.5em 0.1.1.0.5em BERT Bidirectional Encoder Representations from Transformers CERT/CC Computer Emergency Response Team Coordination Center CVE Common Vulnerabilities and Exposures CTI Cyber Threat Intelligence DARPA Defense Advanced Research Projects Agency EDR Endpoint Detection and Response GAN generative adversarial network GPT Generative pre-Trained Transformer IVAM Investigation, Validation, Active Monitoring LIME Local Interpretable Model-agnostic Explanation MTTR Mean Time to Repair/Respond/Remediate ONNX Open Neural Network Exchange SIEM Security Information and Event Management SOAR Security Orchestration, Automation, and Response TTP tactics, methods and procedure 4 Methods 4.1 Egg measurements We measured a total of 1990 eggs from 409 clutches across four species of the shrike family, Laniidae. This included 1313 eggs from 284 clutches of the red-backed shrike, 337 eggs from 60 clutches of the woodchat shrike, 221 eggs from 43 clutches of the lesser grey shrike, and 119 eggs from 22 clutches of the great grey shrike. We determined clutch size parameters based on information provided on museum labels. We excluded nests with incomplete or uncertain data, such as ambiguous collection year, location, or maternal origin. This also ensured that no multiple clutches from the same female were included. We collected egg measurements from six locations housing oological collections: five in Poland and one in Germany. These included: (1) Świętokrzyski National Park in Bodzentyn, Poland (BDZ-PL); (2) Count Antoni Ostrowski Museum in Tomaszów Mazowiecki, Poland (TMZ-PL); (3) Museum and Institute of Zoology Polish Academy of Science, Research Station in Palmiry, Poland (PAL-PL); (4) Museum of Natural History at the University of Wrocław, Poland (WRO-PL); (5) Jacek Malczewski Museum in Radom, Poland (RAD-PL); and (6) Senckenberg Natural History Collections in Dresden, Germany (DRS-DE). Based on the information provided on museum labels, we determined collection localities for 290 clutches collected between 1888 and 1973; clutches with incomplete or ambiguous data, or cases where the collection site could not be reliably identified, were excluded (Figure 5). All eggs used in this study were blown specimens stored in closed cabinets without exposure to light. Measurements were taken after temporarily removing the eggs from the display cases. We measured each egg’s maximum length and width to the nearest 0.01 mm with a Mitutoyo electronic sliding calliper (Kanagawa, Japan) and determined shell weight with a Kern & Sohn GmbH balance (Balingen, Germany). All measurements were taken by a single researcher (KD), ensuring consistency and eliminating inter-observer variability. The dimensions obtained – length (L) and width (W) – were used to calculate five geometrical parameters with the use of the following formulas: (1) the egg shape index (SI): SI = (W / L) x 100 (Sarica and Erensayin, 2004); (2) the geometric mean diameter of eggs (Dg): Dg = (L x W 2 ) ⅓ (Mohsenin, 1970); (3) the surface area of eggs (S): S = π x Dg 2 (Mohsenin, 1970; Baryeh and Mangope, 2003); (4) the degree of sphericity of eggs (Φ): Φ = (Dg / L) x 100; (5) and the volume of eggs (V): V = (π / 6) x L x W 2 (Hoyt, 1979; Severa et al. , 2013; Kumbar et al. , 2016). 4.2 Statistical analysis Initially, we assessed the normality of our data using the Shapiro–Wilk test. Given that the data did not meet the normality assumption, even after attempting appropriate transformations, we proceeded with the Kruskal-Wallis ANOVA test (hereafter KW) to identify differences in egg size parameters. We used generalised linear mixed models (GLMMs) with a Conway–Maxwell–Poisson to evaluate the effects of species, year of egg collection, and egg size on the clutch. The country was included as a random intercept. We analysed determinants of clutch size at the clutch level, using only averages of egg traits per clutch. Because egg size metrics were highly collinear (length, width, diameter, surface area, volume), we adopted a “one variable per construct” rule and retained mean egg volume as the single size proxy. Fixed effects were year, species, and mean egg volume. Models were fitted in R using the package glmmTMB (Brooks et al. , 2017). To evaluate whether the COM-Poisson distribution was appropriate, we fitted alternative GLMMs with identical fixed and random effects structures but assuming Poisson and negative binomial (nbinom2) error distributions, and compared models using Akaike’s information criterion (AIC). The nbinom1 model failed to converge and was therefore not considered further. Model diagnostics were performed using the package DHARMa (Hartig, 2024), based on simulated scaled residuals. We tested for dispersion, zero inflation, and deviations from a uniform distribution of residuals, and inspected residual plots visually. Residual diagnostics using DHARMa (dispersion = 0.97, p = 0.98; zero-inflation test ratioObsSim ≈ 1, p = 1; some deviations from uniformity) and the overdispersion check in the performance package (Lüdecke et al. , 2024) (dispersion ratio = 0.96, p = 0.95) indicated no overdispersion or zero inflation and a mild tendency towards underdispersion. We therefore modelled clutch size using a GLMM with a COM-Poisson distribution and log link in the glmmTMB package (Brooks et al. , 2017), retaining species, year and mean egg volume as fixed effects and including country as a random intercept. For each response variable (egg traits), we quantified temporal change within the analysed subset by fitting an ordinary least squares (OLS) linear regression of egg traits on a calendar year. For the traits with significant temporal differences, we applied additional analysis. We repeated the test using heteroscedasticity-robust SEs and a robust Theil–Sen estimator; finally, if needed (results not clear), we applied a generalised additive model. All statistical analyses were performed using R statistical computing software 4.1.2 R Core Team (R Core Team, 2021). Figures Figure 1. The four shrike species analysed: (a) red-backed shrike Lanius collurio (pair – female [left] and male [right]) (©Cezary Korkosz); (b) woodchat shrike L. senator (©Cezary Korkosz); (c) lesser grey shrike L. minor (©Maciej Kowalski); (d) great grey shrike L. excubitor (©Małgorzata Łuczkiewicz). Photos show adult birds. Figure 2. Egg size analysis among shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, great grey shrike; egg length (mm), width (mm); dots coloured according to the species and scaled according to the shell weight (g). Figure 3. Comparison of egg traits among shrikes: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. Panels show: egg length (mm); egg width (mm); shape index; degree of sphericity; egg diameter (mm); egg volume (cm³); egg surface area (cm²); shell weight (g). Boxplots show the interquartile range (IQR), median (horizontal line), and whiskers extending to 1.5×IQR; jittered points indicate individual eggs. Colours distinguish species. Uppercase letters above boxes denote groups from Dunn’s post-hoc tests with Bonferroni correction (α = 0.05); species that do not share a letter differ significantly. Figure 4. Temporal trends in egg traits and clutch size of red-backed shrike (1888–1975). Each panel shows annual values with a fitted linear trend (ordinary least squares); panel annotations report the p-value, slope (per year), and R². Studied feature egg length, width, shell weight, surface area, volume, shape index, degree of sphericity and clutch size. The “N records” and “Sampling across years” panels summarise temporal sampling effort. Figure 5. Geographic distribution of 290 clutches of red-backed shrike, woodchat shrike, lesser grey shrike and great grey shrike collected between 1888–1973 from six oological collections (BDZ-PL, TMZ-PL, PAL-PL, WRO-PL, RAD-PL, DRS-DE). Numbers in parentheses represent the total number of clutches with determined location held in each collection. Different symbol shapes and colours denote individual collections (see legend), and symbol size is proportional to the number of clutches per locality. Table 1. Descriptive statistics for egg traits in four shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. For each studied trait and species, the table reports sample size ( n ), mean, standard deviation (SD), median, and standard error of the mean (SE). Traits include clutch size; egg width, diameter, length, degree of sphericity, shape index, shell weight, surface area, and volume. Units: linear dimensions in mm, mass in g, surface area in cm², and volume in cm³. Table 2. Results of the generalized linear mixed model (GLMM; Conway–Maxwell–Poisson distribution) examining the effects of species, scaled year of egg collection, and mean egg volume on clutch size, with country included as a random intercept. Estimates, 95% confidence intervals (CI), p-values, random-effect variance components, and model fit statistics are shown. verbose, tmargin=2.3cm, bmargin=3.4cm, lmargin=1.5cm, rmargin=1.5cm, headheight=1.25cm, footskip=1.25cm \geometryright=1.5cm 00 0.1.0.5em 0.1.1.0.5em BERT Bidirectional Encoder Representations from Transformers CERT/CC Computer Emergency Response Team Coordination Center CVE Common Vulnerabilities and Exposures CTI Cyber Threat Intelligence DARPA Defense Advanced Research Projects Agency EDR Endpoint Detection and Response GAN generative adversarial network GPT Generative pre-Trained Transformer IVAM Investigation, Validation, Active Monitoring LIME Local Interpretable Model-agnostic Explanation MTTR Mean Time to Repair/Respond/Remediate ONNX Open Neural Network Exchange SIEM Security Information and Event Management SOAR Security Orchestration, Automation, and Response TTP tactics, methods and procedure Supplementary materials Figure S1. Among-year variation in egg morphology traits for four shrike species, red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike, based on historical museum collections spanning 1888–1973. Each panel presents non-parametric comparisons (Kruskal–Wallis test followed by Dunn’s pairwise post-hoc tests) for key reproductive traits, including egg length, width, shell weight, shape index, volume, and clutch size. Boxes show interquartile ranges with medians, whiskers indicate data spread, and letters denote statistically significant differences among years ( p < 0.05). P-values from Kruskal–Wallis tests are provided in each panel. Figure S2. Geographic variation in egg morphology traits of four shrike species, red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike, across countries represented in the historical egg collection. Each panel shows mean values (± variation) of key egg traits – including egg length, width, diameter, surface area, volume, shell weight, shape index, degree of sphericity, and clutch size – plotted by country. Sample sizes (n) for each country are indicated below the x-axis. Figure S3. Boxplots showing variation in mean egg traits (length, width, shell weight, shape index, diameter, surface area, degree of sphericity, and volume) among shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. Each box represents the interquartile range (IQR) with the median indicated by a horizontal line, whiskers extending to 1.5× IQR, and outliers shown as individual points. Figure S4. Correlation heatmaps showing relationships among clutch size and mean egg traits (length, width, shell weight, shape index, diameter, surface area, degree of sphericity, and volume) across all studied species (ALL) and separately for red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. Colour gradients represent Pearson correlation coefficients ranging from −1 (negative correlation, blue) to +1 (positive correlation, red). Table S1. Results of pairwise Wilcoxon rank-sum tests comparing egg and clutch traits between years for each shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. The table includes trait name, compared years, raw ( p ) and adjusted p -values, sample sizes for each year, and significance levels. Table S2. Results of pairwise Wilcoxon rank-sum tests comparing egg and clutch traits between countries for each shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. The table includes trait name, compared years, raw ( p ) and adjusted p -values, sample sizes for each year, and significance levels. Table S3. Pearson correlation coefficients ( r ) between clutch and egg traits calculated across all species and separately for each shrike species: red-backed shrike, woodchat shrike, lesser grey shrike, and great grey shrike. The table lists pairs of variables, sample size ( n ), correlation coefficient ( r ), raw p -values, and Benjamini–Hochberg adjusted p -values. verbose, tmargin=2.3cm, bmargin=3.4cm, lmargin=1.5cm, rmargin=1.5cm, headheight=1.25cm, footskip=1.25cm \geometryright=1.5cm 00 0.1.0.5em 0.1.1.0.5em BERT Bidirectional Encoder Representations from Transformers CERT/CC Computer Emergency Response Team Coordination Center CVE Common Vulnerabilities and Exposures CTI Cyber Threat Intelligence DARPA Defense Advanced Research Projects Agency EDR Endpoint Detection and Response GAN generative adversarial network GPT Generative pre-Trained Transformer IVAM Investigation, Validation, Active Monitoring LIME Local Interpretable Model-agnostic Explanation MTTR Mean Time to Repair/Respond/Remediate ONNX Open Neural Network Exchange SIEM Security Information and Event Management SOAR Security Orchestration, Automation, and Response TTP tactics, methods and procedure Acknowledgements We are deeply grateful to Dr Jan Reklewski, Head of Swietokrzyski National Park, Bodzentyn, Poland; MSc Krzysztof Jednac, Head of Count Antoni Ostrowski Museum in Tomaszow Mazowiecki, Poland; Prof. Dariusz Iwan, Head of the Zoological Museum at the Museum and Institute of Zoology of the Polish Academy of Sciences in Warsaw, Palmiry, Poland; Prof. Jan Kotusz, Head of Museum of Natural History, University of Wroclaw, Poland; MSc Leszek Ruszczyk, Head of Jacek Malczewski Museum in Radom, Poland; Prof. Uwe Fritz, Head of Senckenberg Natural History Collections Dresden, Germany, for their courtesy and allowing access to oological collections. 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Crossref Google Scholar Information & Authors Information Version history V1 Version 1 09 April 2026 Copyright This work is licensed under a Non Exclusive No Reuse License. Keywords ecosystem evolutionary ecology natural history vertebrate Authors Affiliations Paweł Pstrokoński 0000-0003-2728-2223 Warsaw University of Life Sciences View all articles by this author Katarzyna Roguz University of Warsaw View all articles by this author Wojciech Wójcik Warsaw University of Life Sciences View all articles by this author Martin Päckert 0000-0001-5045-0139 Senckenberg Natural History Collections View all articles by this author Joanna Rosenberger 0000-0001-8169-6377 Wrocław University of Environmental and Life Sciences View all articles by this author Dominika Mierzwa-Szymkowiak Museum and Institute of Zoology Polish Academy of Sciences View all articles by this author Magdalena Sepkowska Count Antoni Ostrowski Museum in Tomaszow Mazowiecki View all articles by this author Jan Lontkowski Museum of Natural History, Wroclaw University View all articles by this author Marek Słupek Museum of Jacek Malczewski in Radom View all articles by this author Michał Chiliński 0000-0002-3496-9966 Faculty of Biology Univeristy of Warsaw View all articles by this author Damaziak Krzysztof [email protected] Warsaw University of Life Sciences View all articles by this author Metrics & Citations Metrics Article Usage 246 views 95 downloads .FvxKWukQNSOunydq8rnd { width: 100px; } Citations Download citation Paweł Pstrokoński, Katarzyna Roguz, Wojciech Wójcik, et al. 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