The Momentum Vegetation and Seedbank Dynamics Research Group at the ELKH Centre for Ecological Research (CER) was the first to investigate the impact of cranes on grassland ecosystems, and to reveal the important habitat-converting role of this bird species. In studies carried out in the Hortobágy National Park, researchers have shown that ploughing by cranes also has a major landscape-level effect on ecosystem functioning, creating new patches with different structures and species composition. A paper presenting the results of the research was published in the journal Land Degradation and Development.
In nature, organisms have complex and intricate relationships with one another. Among them, those that have a particularly high impact on the species that co-occur with them are called ecosystem engineers. Corals, for example, are well known for providing habitats for many aquatic communities on their reefs, or beavers for transforming their environment through engineering. The known engineers of the bird world are woodpeckers, whose burrows are used by songbirds. In grassland habitats, however, researchers have as yet found no examples of birds’ significant ecosystem-engineering activities.
The global population of cranes has fortunately increased significantly in recent decades, thanks to European-level conservation measures, wetland restoration and the crane’s excellent adaptability. As a result, the impact of these large birds on natural ecosystems is expected to increase, which is why it is important to better understand the ecological role of cranes in grassland habitats.
Hungary is an important place for crane migration, with up to 100-160 thousand birds observed in the autumn in the lowlands. Cranes feed mainly on cornfields, but often go out to grasslands where they supplement their diet with arthropods. In search of ground-dwelling invertebrates, the birds use their beaks to cut the soil and vegetation, creating ‘crane ploughing’ areas. The areas disturbed are usually a few square metres, but in some places they can cover several hectares. Crane ploughing areas are a characteristic landscape feature of salt marshes, but their ecological role in the landscape has been unknown to date.
Researchers have now compared the vegetation of crane ploughing areas and undisturbed salt marshes in the Hortobágy National Park. It was found that the patches where bird activity was high had persistently less plant cover than the undisturbed grasslands. Interestingly, significant changes have been observed not only in vegetation structure, but also in the species composition of the vegetation and the functioning of the ecosystem. Compared to the surrounding areas, vegetation emerged earlier on the crane ploughs, mainly composed of dicots and perennial species. There was a significant presence of insect-pollinated plants, which provide an important food source for pollinator communities. These pioneer patches were characterized by a higher richness of species and a species composition different from that of closed grasslands. In addition, the lush vegetation that has previously sprouted can be an important source of fodder for grazing animals during the dry period in early spring. However, in late summer, the forage value of the crane plough vegetation is lower than that of the surrounding unploughed grassland.
Researchers have shown that crane ploughing also significantly alters ecosystem functioning at the landscape level, creating new patches with different structure and species composition. For grassland bird species, a similar level of habitat engineering activity has not been known until now. It is particularly interesting that while birds have this significant impact in just a few weeks, their activities determine the composition and structure of the vegetation for years, and thus presumably affect the whole community.
Valkó, O., Borza, S., Godó, L., Végvári, Z., Deák, B. (2022) Eurasian crane (Grus grus) as ecosystem engineer in grasslands ‒ conservation values, ecosystem services and disservices related to a large iconic bird species. Land Degradation and Development https://doi.org/10.1002/ldr.4314