Seasonal changes in distribution and abundance of a local Corncrake population

Abstract

AbstractMany bird species have experienced short- or long-term population declines. However, the mechanisms and reasons underlying such negative changes are often not fully understood, making it difficult to identify effective conservation measures to recover populations. In this study, we focused on local changes in the abundance and distribution of calling male Corncrakes Crex crex in relation to: (1) within- and between-season site fidelity of adult males, (2) spatial distribution of territories in consecutive years and (3) the effect of habitat conditions on population size. We counted the number of calling males at ten randomly selected study plots (1 km2) in 2014–2018. Additionally, males were caught and individually marked in years 2015–2017. We found significant between-year changes in Corncrake abundance, from a 34% decrease to a 21% increase. On average, 32% of males established territories in the same locations as males recorded in the previous year. Breeding site fidelity was very low, with only 2–5% of males recaptured in the following year. Males selected areas characterized by higher values of NDVI (Normalized Difference Vegetation Index–higher values indicate more biomass) than on average within the study area. Population size in a particular year was significantly affected by the NDVI of the previous year but not by the NDVI in the current breeding season. We suppose that Corncrakes may exhibit a nomadic breeding behavior, and settle at territories when they encounter optimal habitat conditions. Moreover, as population size was negatively correlated with habitat conditions at the beginning of the previous breeding season, we suppose that local population changes may reflect more general trends in a whole population rather than local breeding success. Therefore, we highlight the need for better knowledge of Corncrake dispersal within the main European population and for the coordination of monitoring and conservation efforts, especially in those regions where most Corncrakes breed.