Data from: Effect of composition on shape of bird eggs

Numerous studies over the past 90 years have described the various bird egg shapes in mathematical terms but few studies have considered the underlying reasons for such interspecific egg shape variability. This study investigated how the size and composition, i.e. proportions of shell, yolk and albumen, were associated with egg shape. Geometric morphometrics were used to generate principal components, which were analysed in relation to taxonomy (i.e. avian order) and degree of neonatal developmental maturity, which correlates with egg composition. The analysis confirmed previous results that most of the variation in shape is associated with degree of elongation (i.e. length divided by breadth) and asymmetry (i.e. position of the broadest part of the egg away from the mid-point of the egg's length). Egg shape reflected avian order but not developmental maturity. The degree of elongation of an egg is related to absolute egg mass and the proportion of yolk. By contrast, the degree of asymmetry is related to the proportion of shell and the mass of the egg relative to female body mass. Although significant, the models explained little of the variation in egg shape and so it was concluded that other factors, such as pelvis size and shape, could be more important in determining egg shape in birds.近90年来，诸多研究已从数学维度对各类鸟类的卵形态展开描述，但鲜有研究探讨种间卵形差异的内在成因。本研究围绕卵的大小与组成（即卵壳、卵黄与卵清的占比）与卵形的关联展开探究。研究采用几何形态测量学（Geometric Morphometrics）方法生成主成分（Principal Components），并结合分类学（即鸟类目级类群）以及与卵组成相关的雏鸟发育成熟度开展分析。分析结果验证了既往研究结论：卵形的大部分变异与伸长程度（即长径除以短径）及不对称性（即卵最宽处偏离卵长轴中点的位置）相关。卵形与鸟类所属目级类群相关，但与雏鸟发育成熟度无关。卵的伸长程度与绝对卵重及卵黄占比呈关联；相对而言，卵的不对称程度与卵壳占比以及卵重相对于雌鸟体重的比值相关。尽管所构建的模型具备统计学显著性，但仅能解释少量卵形变异，因此研究得出结论：诸如骨盆尺寸与形态等其他因素，或许在决定鸟类卵形方面发挥更为关键的作用。