Department of Applied Ecology, St. Petersburg State University, Universitetskaya Emb. 7-9, St. Petersburg, 199034, Russia.
Zoological Institute RAS, Universitetskaya Emb. 1, St. Petersburg, 199034, Russia.
BMC Ecol Evol. 2024 Feb 2;24(1):17. doi: 10.1186/s12862-024-02204-7.
The quality of swans' nutrition at spring migration stopovers is important for their successful breeding. It is of great interest to study the differences in nutrition of different swan species when sharing the same habitat. Microscopic analysis of Cygnus olor, C. cygnus, and C. columbianus bewickii feces collected in the eastern part of the Gulf of Finland in February-April 2014-2019 was performed. We measured food preferences of the three swan species using non-metric multidimensional scaling (NMDS). The width and overlap of dietary niches were also calculated. The diet of C. olor consists almost entirely of soft submerged aquatic vegetation, mainly macroalgae. Samples of the other two species except macroalgae contained large amounts of young shoots and roots of rigid semi-submerged and coastal vegetation. The dietary niche of C. cygnus is the most isolated because it is dominated by thick rhizomes of Phragmites australis, which are hardly used by other swan species. The diet of Bewick's swans was similar in many respects to that of the Mute swan, but Bewick's swans much more often preferred vegetative parts of submerged and semi-submerged plants, such as Stuckenia pectinata, Potamogeton perfoliatus, Sparganium sp., Nuphar lutea, and others. Notably, the dietary niches of Mute swan and Whooper swan overlapped as much as possible in February March during a period of severe food shortage, in contrast to later periods in spring when food was more abundant and varied. In general, differences in diets are well explained by differences in the morphology of birds. Comparison of tarsometatarsus indices shows that C. olor is the most water-related species. C. olor has the longest neck and its beak has the strongest filter features, whereas beaks of the other two species shows noticeable "goose-like grazing" features. Moreover, C. Cygnus has the most powerful beak. These features are due to the history of species. The formation of C. olor occurred during the Miocene-Pliocene of the Palaearctic in the warm eutrophic marine lagoons of the Paratethys with abundant soft submerged vegetation. The evolution of C. cygnus and C. c. bewickii took place in Pleistocene. At that time, periglacial and thermokarst water bodies on permafrost became widespread in the Palearctic, as well as dystrophic peat lakes with much poorer submerged aquatic vegetation, but well-developed coastal and semi-submerged vegetation.
在春季迁徙中途停留地，天鹅的营养质量对其成功繁殖至关重要。研究在共享同一栖息地时不同天鹅物种的营养差异非常有趣。对 2014 年至 2019 年 2 月至 4 月在芬兰湾东部收集的 Cygnus olor、C. cygnus 和 C. columbianus bewickii 粪便进行了微观分析。我们使用非度量多维尺度（NMDS）测量了三种天鹅的食物偏好。还计算了饮食生态位的宽度和重叠。C. olor 的饮食几乎完全由柔软的水下植被组成，主要是大型藻类。除了大型藻类外，其他两种物种的样本还含有大量的硬半淹没和沿海植被的幼芽和根。C. cygnus 的饮食生态位最为孤立，因为它主要由芦苇厚厚的根茎组成，其他天鹅物种很少使用。Bewick's swans 的饮食在许多方面与 Mute swan 的饮食相似，但 Bewick's swans 更经常喜欢水生和半水生植物的营养部分，如苦草、菹草、三棱草、黄花狸藻等。值得注意的是，在食物严重短缺的 2 月至 3 月期间，Mute swan 和 Whooper swan 的饮食生态位重叠最多，而在春季后期，食物更加丰富和多样化。一般来说，饮食差异很好地解释了鸟类形态的差异。跗跖骨指数的比较表明，C. olor 是最亲水的物种。C. olor 拥有最长的脖子和最强的过滤特征，而其他两种物种的喙则具有明显的“鹅式放牧”特征。此外，C. Cygnus 的喙最有力。这些特征是由于物种的历史。C. olor 的形成发生在古近纪-上新世的帕拉提斯海洋温暖富营养的泻湖中，那里有丰富的柔软水下植被。C. cygnus 和 C. c. bewickii 的进化发生在更新世。当时，在北极地区，冰缘和热喀斯特水体在永冻土层上广泛分布，还有营养贫乏的泥炭湖和发育良好的沿海和半淹没植被。
