Changing climate is affecting life all over the world. The loggerhead turtle (Caretta caretta) is one of the most vulnerable turtle species to climate change, particularly with regard to sex determination being affected by high temperatures in most nesting areas, such as the Cuban archipelago. As yet, species information is scarce for the Cuban archipelago as a whole. This study provides information about loggerheads in order to determine the possible effects of climate change on this species, especially in Guanahacabibes. We monitored 10 beaches along the southernmost coast of the Guanahacabibes Peninsula for 18 yrs (1998–2015), from May to September of each year, to determine nesting activity and density. Females were measured and tagged and the remigration interval was determined. Temporal variation was reflected in apparent peaks in reproductive activity on a biennial cycle. We found intraseasonal variation with the highest nesting activity in June, with a 15% increase in nesting activity in the second half of that month. Reduction in clutch size, incubation period, and hatchling size, as well as a potential feminization of hatchling production, indicates a possible effect of climate change in reproductive success. Our results are a first attempt at characterizing Guanahacabibes populations and have great value for establishing conservation priorities such as the protection of the nesting females and control of incubation environment in the face of global climate change within the context of national management plans.