Eggs of extinct dwarf island emus retained large-size: Electronic supplementary material

Islands off southern Australia once harboured three subspecies of the mainland emu (Dromaius novaehollandiae), the smaller Tasmanian emu (D. n. diemenensis), and two dwarf emus, King Island emu (D. n. minor) and Kangaroo Island emu (D. n. baudinianus), which all became extinct rapidly after discovery by human settlers. Little was recorded about their life histories and only a few historical museum specimens exist, including a number of complete eggs from Tasmania and a unique egg from Kangaroo Island. Here we present a detailed analysis of eggs of dwarf emus, including a first record of an almost complete specimen from King Island. Our results show that despite the reduction in size of all island emus, especially the King Island emu that averaged 44% smaller than mainland birds, the egg remained similar-sized in linear measurements, but less in volume and mass, and had slightly thinner eggshell. We provide possible reasons why these phenomena occurred.

澳大利亚南部近海岛屿曾栖息有澳洲大陆鸸鹋（Dromaius novaehollandiae）的三个亚种：体型较小的塔斯马尼亚鸸鹋（D. n. diemenensis），以及两种矮鸸鹋——金岛鸸鹋（D. n. minor）与袋鼠岛鸸鹋（D. n. baudinianus）。这些类群在被人类定居者发现后均迅速走向灭绝。此前关于它们的生活史记录极少，现存的历史馆藏标本也寥寥无几，其中包括多枚来自塔斯马尼亚的完整鸸鹋蛋，以及一枚来自袋鼠岛的孤本鸸鹋蛋。
我们在此对矮鸸鹋的蛋展开详细分析，其中还首次报道了一枚来自金岛的近乎完整的矮鸸鹋蛋标本。研究结果显示，尽管所有岛屿鸸鹋的体型均有所缩小——尤其是金岛鸸鹋，其平均体型较大陆鸸鹋小44%——但它们的鸸鹋蛋在线性尺寸上仍与大陆种群相近，仅在体积与重量上有所降低，且蛋壳厚度略薄。我们针对上述现象的潜在成因给出了可能的解释。