Habitat use and foraging parameters of breeding Skylarks indicate no seasonal decrease in food availability in heterogeneous farmland

Reduced food availability during chick raising is a major driver of farmland bird declines. For the Eurasian Skylark (Alauda arvensis), food availability is determined by various factors (i.e., arthropod abundance/diversity, accessibility of the vegetation, distance to foraging sites). In modern farmland, it is supposed to decrease over the breeding season due to less penetrable vegetation. We explored foraging habitat selection by chick-raising Skylarks with a focus on the seasonal dynamics of habitat use and food availability. We investigated i) habitat selection concerning prey biomass/diversity, vegetation cover, and distance to foraging sites, ii) the overall and seasonal habitat use, and iii) seasonal developments of foraging parameters (e.g., the feeding frequency) as indicators of food availability. We collected data on foraging habitats and foraging parameters of chick-raising Skylark pairs at 51 nests from a Central European population in 2018 and 2019. Prey biomass/diversity and vegetation cover were measured for all habitats around 42 of these nests. As revealed by multivariate and compositional analyses, Skylarks mainly selected foraging habitats based on the proximity to nests. The most frequent habitats within home ranges could not be ranked according to an overall importance for foraging and their use partially changed over time. The feeding frequency increased throughout the breeding season, while other foraging parameters did not show significant changes. In contrast to our expectations, our data indicated therefore an increase, not a decrease in food availability in the late breeding season. This also implies that the habitat use was constantly suitable to raise offspring. We interpret this to be a consequence of the heterogeneous farmland composition of the study area that enabled Skylarks to establish a diverse home range and to benefit from synergetic effects of neighboring habitat types. Thus, our findings provide support for the high importance of crop diversity in Skylark conservation.

雏鸟育雏期食物可获得性下降是农田鸟类种群衰退的主要驱动因素。对于欧亚云雀（Eurasian Skylark，学名Alauda arvensis）而言，食物可获得性由多种因素决定，包括节肢动物丰度与多样性、植被通透性、与觅食位点的距离。在现代农业田中，由于植被通透性下降，学界曾推测育雏期食物可获得性会随繁殖季推移逐渐降低。本研究以育雏期欧亚云雀为研究对象，探讨其觅食生境选择，重点关注生境利用与食物可获得性的季节动态。我们开展了三项研究内容：一是针对猎物生物量/多样性、植被盖度以及与觅食位点的距离开展生境选择分析；二是探究整体及季节尺度下的生境利用模式；三是分析作为食物可获得性指标的觅食参数（如饲喂频次）的季节变化趋势。本研究于2018年与2019年，针对中欧种群的51个云雀巢，收集了育雏云雀配偶对的觅食生境与觅食参数数据。其中，针对其中42个巢周边的所有生境，均测定了猎物生物量/多样性与植被盖度。通过多变量分析与组成分析结果显示，欧亚云雀主要依据巢址的邻近性选择觅食生境。家域内出现频率最高的生境无法依据其觅食总重要性进行排序，且其利用模式随时间发生了部分变化。整个繁殖季内，饲喂频次呈上升趋势，但其余觅食参数未出现显著变化。与我们的初始假设相悖，本研究数据显示，繁殖季后期的食物可获得性反而升高，而非降低。这同时表明，云雀的生境利用始终适宜雏鸟育雏。我们认为，这一结果源于研究区域内农田生境的异质性结构：该结构允许欧亚云雀构建多样化的家域，并从相邻生境类型的协同效应中获益。因此，本研究结果佐证了作物多样性在欧亚云雀保护工作中的极高重要性。