Agricultural expansion at the expense of natural habitats and the intensification processes in agricultural production are globally among the main causes of biodiversity and ecosystem services loss at large scale. This process can completely alter food provision for birds and have negative consequences for their diet and breeding performance. Under the hypothesis that changes in land use limit food resources for raptors, our aim was to analyze variation in nestling diet between natural areas and areas with different degrees of agricultural intensification (natural forest, traditional farmland, intensive farmland) in a population of American Kestrel Falco sparverius breeding in nest boxes and cavities. Through the analysis of pellets and prey remains collected during the reproductive season of 2012–2013 we found no differences in diet diversity among areas and the diet in the three areas was monopolized by arthropods. However, the diet did change in composition between areas. Numerically, Orthoptera dominated the diet in the three areas, although with a higher percentage in the forest area. The frequency of vertebrate consumption was affected positively by the area occupied by natural forest and stubble, while the soybean cover affected the consumption in a negative way. In both agricultural areas, the diet was complemented with different groups of arthropods suggesting that changes in land use generate a functional response in the American Kestrel that is able to take advantage of available resources in each sampling area. Long-term analysis of diet variation within the framework of agricultural intensification and its relation with demographic parameters and individual performance will allow to evaluate the impact of this variation in the diet on kestrels.