4.5. Potential role of agricultural intensification in the decline of Ortolan Bunting
Our results show the importance of specific habitat characteristics such as high crop type diversity and availability of bare ground for the Ortolan Buntings. These preferred habitat characteristics are more typical for traditional, small-scale farming. The results also highlight regional variations. Notably, regions with higher agricultural intensification, like South-West Finland, showed lower population growth rates, suggesting a potential link between intensification and population decline. The fields occupied by Ortolan Buntings in North Ostrobothnia are usually rather new fields and have thus not been under intensive agricultural management as long as the fields occupied by Ortolan Buntings in South-West Finland have.
Agricultural intensification may have detrimental effects on biodiversity through several means. Concerning the Ortolan Bunting, reductions in prey availability or accessibility due to habitat deterioration on the breeding grounds could be one of the main reasons behind the negative population growth rate of the species. Also, the role of nest predators might have changed due to habitat deterioration caused by agricultural intensification. Habitat change might have forced birds to nest in unsafe habitat types or reduced availability of alternative food sources may have caused generalist predators to change their diets (Evans, 2004). Krüger et al. (2018) showed that the Raccoon Dog (Nyctereutes procyonoides ) is a potential new mammalian nest predator successfully invading agricultural habitats in Finland. The Raccoon Dog has colonized the country within the past 70 years, starting from the Southeast Finland and now has a distribution which covers most of Finland, except the northernmost parts (Kauhala and Kowalczyk, 2011). However, the densities of Raccoon Dogs are not yet high in the North Ostrobothnia region (Natural Resources Institute Finland, 2022), which could partly explain the higher growth rates of Ortolan Bunting there. Another, potentially also very damaging, predator is the feral cat which probably has an equal effect in all regions. The impact of increasing effectiveness of plant protectants (pesticides, herbicides, insecticides etc.) on the breeding and survival of Ortolan Buntings also remains unknown. Eng et al. (2019) studied the effect of neonicotinoids on migrating White-crowned Sparrows. They found that ingestion of imidacloprid by the birds during migratory stopover caused a rapid reduction in food consumption, mass and fat, and delayed their departure.
In summary, although our study did not directly investigate the relationship between the level of intensity of agricultural practices and the population growth rate of Ortolan Bunting, our results, however, suggest a potential adverse impact of agricultural intensification on the decline of this species.
5. CONCLUSIONS AND CONSERVATION IMPLICATIONS
Current conservation efforts in farmland areas seem to be ineffective in mitigating the negative effects of agricultural intensification on bird populations. Measures taken so far might simply be too light to influence declining farmland birds. At present, it is often unclear whether current conservation measures have beneficial impacts at all or whether the measures are just inadequate, either at the local scale (too narrow field margins for example) or at the wider scale in which they are applied (too few farms applying the measures).
To conserve the Ortolan Bunting there clearly is a simultaneous need to avoid abandonment of agricultural areas, and to promote “de-intensification” of agricultural practices. This general recommendation would benefit also many other threatened farmland species. However, in the case of this very rapidly declining species, it is evident that more precise and finely targeted conservation actions need to be taken urgently at the remaining and still (somewhat) viable singing group locations.
Based on our results, we recommend applying conservation measures which increase the diversity of crop types. Often a field with a greater diversity of crop plant types also includes more bare ground as a result of various plant structures and related managing practices. Alternatively, if increasing diversity is not feasible, or additionally, we recommend establishing non-crop growing stripes of ploughed bare ground. We also recommend targeting these actions to populations living in interconnected farmland landscapes and in northern parts of the species’ distribution range as it is more likely that these populations act as sources, rather than sinks, of population growth.
In general, we agree with several researchers stating that we need more multi-functional, mixed, agro-ecologically managed agricultural landscapes that promote agricultural yield, biodiversity, and ecosystem services to conserve biodiversity in farmlands (Baudron et al., 2019; Tscharntke et al., 2012; Wilson et al., 1997).