Weak influence of natural vegetation in urban green spaces compared to agricultural ecosystems on House Martin populations: Insights from nationwide citizen science data in the Czech Republic

The House Martin (Delichon urbicum) is a common farmland bird species in the European landscape, yet its population numbers are currently in decline. However, it is not yet sufficiently explained why this long-term decline occurs. To fill this gap in our knowledge, we investigated how land cover composition affects the abundance of House Martins on the landscape scale by using nationwide citizen science data. Utilizing a generalised linear mixed-effect model (GLMM), we evaluated 12,094 records from the Czech Republic spanning 2009–2017. Our analysis underscores the significance of land cover type in shaping House Martin abundance. More specifically, our results indicate that within agricultural land covers "naturally managed arable lands" exhibited significant positive effect, while forests, orchards, and vineyards were deemed less favourable for House Martin populations. Within urban land covers, we found a clear distinction in the impact on House Martin populations, with a positive effect observed in urban infrastructure, development areas, and post-industrial sites (i.e., UrbanAreas), while an indifferent impact was noted within urban green spaces and landscaped areas (i.e., GreenUrban). Notably, our findings suggest that the simple spatial, age, and species structure typical of forests in Europe, and similarly, the uniform structure of parks and gardens, may be responsible for the decline in the abundance of the House Martin. We advocate for the preservation or enhancement of urban greenery, expansion of natural vegetation in rural areas and adoption of ecological management practices in orchards and vineyards to mitigate further declines in House Martin populations.