Laid eggs in vain got eaten by a crane? : Investigating habitat selection and activity by Common cranes to consider potential impact on other wetland bird species

Wetland species are declining and efforts are being made to protect wetlands and their biodiversity. In Europe, these efforts could be hampered by the recent rise in the Western European Common crane (Grus grus) population. Increasing anecdotal evidence has raised concerns that this population increase has led to an increase in crane predation on other bird species’ eggs and chicks. This study aims to investigate, weather cranes are a potential threat to other bird species by predating on eggs and chicks, and ultimately biodiversity. Proxies, like habitat selection and time devoted to foraging in wetlands, were used to investigate risk of crane predation. Habitat selection and time devotion were studied using location data derived from 13 GPS-tagged Common cranes during May and June in 2017 to 2019. Observational foraging data was collected in the protected wetland Kvismaren, Sweden in June 2019, including adult non-breeding cranes only. During daytime, the three habitats with highest mean relative probability of presence within a 95% confidence interval for cranes are open wetland (0.87, CI: 0.86-0.89), followed by inland water (0.60, CI: 0.56-0.63) and arable land (0.55, CI: 0.52-0.59). The proportion of time cranes spend in wetlands is 0.39 in May and 0.28 in June. Cranes spend a proportional majority of their time (0.69) on foraging behavior compared to other activities they perform in wetlands. Since every encounter with a chick or egg can end in predation and cranes spend most of their time foraging in wetlands a population increase in cranes could have severe impact on bird species. Future research should take into account crane diet, which categories of cranes (e.g., non-breeding versus breeding) are most likely to predate on eggs and chicks and the negative impact on bird populations in relation to crane numbers to fill in the major research gap in this field. Lastly, future studies should evaluate how an increasing crane population also could impact the abundances of other wetland species such as, rodents, amphibians, fish and invertebrates