White Storks nest at high densities near landfills changing stork nesting distributions in the last four decades in Central Spain

Human-induced environmental changes are the main drivers of the ongoing redistribution of biodiversity. The millions of tons of organic waste that is added daily to landfills can increase the carrying capacity of ecological systems with direct effects on species' population sizes and/or distributions. Understanding the effect of landfills on bird distribution is essential to assess management decisions. Our aim was to determine the role of landfills in the distribution of the breeding population of White Storks (Ciconia ciconia) in the last 4 decades. For that purpose, we used historical and current census data of breeding pairs before and after landfill exploitation. In this study, we found that landfills have altered the distribution of the breeding population over the last 4 decades in the province of Madrid, Spain. We found that birds occupied new nesting sites near landfills independently of habitat quality as defined by prey abundance and quality according to the previous studies. Nest density was higher near landfills and increased after the landfills began to be utilized by this species. Population growth and extremely high breeding densities may translate into conflicts with humans, particularly when new nesting sites are in urban areas, and possibly alter the perception of this bird species by the human population. Landfill closures, mandated by the European Landfill legislation, are an opportunity to reduce the effects of landfills on animal populations, and reduce human-wildlife conflicts. However, there must be a process of transition and a preliminary evaluation of habitat quality and suitability in the region to avoid a dramatic decline of the White Stork population. Lay Summary center dot Landfills attract wildlife in high numbers since they are an abundant and predictable anthropogenic food source. This may have an impact on species' population sizes and/or distributions and an increase human-wildlife conflicts. center dot We use historical and current data from the breeding population census in the Madrid region to assess changes in the population distribution of White Storks in the last 4 decades. center dot Density of nests increased near landfills after White Storks started exploiting these facilities. In addition, breeding pairs occupied good-quality habitats and urban areas near landfills from 1984 to 2004, sifting to sub-optimal areas closer to the landfills in the later years. center dot Landfill's closure can be an opportunity to reduce the health, security and safety risks of this facilities for birds and return to former population size numbers. However, this change on landfill management needs to be a gradual process and we recover and manage suitable habitats.