Investigating the influence of parasitic infection on animals requires precise estimates of the infection status of individuals. In the case of intestinal parasites, infection condition is often indirectly determined by the presence and abundance of parasite propagules in faeces. However, parasite shedding is affected by ontogenetic, daily and seasonal patterns that are rarely identified, particularly for nestlings of wild passerines. We investigated the effect of age and time of day on coccidial oocyst shedding in Spotless Starling Sturnus unicolor nestlings and the variation over the breeding season in the prevalence and intensity of coccidial infection. Our study demonstrated that coccidial oocysts can be detected in nestling faeces as early as seven to ten days after hatching but not before. Late afternoon, when prevalence was 98% of samples, was the most likely time to detect coccidial oocysts, compared with a prevalence of 43% in early morning samples. Infection intensity in starling nestlings also increased throughout the day, averaging (± S.E.) 102 ± 27 oocysts per gram of faeces in the early morning to 29,570 ± 7,533 oocysts per gram at the end of the day. Lastly, we observed an increase in infection intensity, in end of day samples, from a mean (± S.E.) of 27 ± 14 oocysts per gram of faeces at the beginning of the season to 27006 ± 5116 oocysts per gram. Also, we found an increase in prevalence of coccidial infection as the season progressed: from 58% at the beginning of the season to 87% at the end. This article provides useful methodological information for future studies of nestlings in free-living avian species. We also report some considerations that may help to establish appropriate protocols to investigate the influence of this type of parasitic infection on different aspects of bird biology, minimising biases and errors.—De la Peña, E., Muriel, J., Gil, D. & Pérez-Rodríguez, L. (2024). Parasite shedding is highly influenced by age, time of day, and sampling date in Spotless Starling Sturnus unicolor nestlings. Ardeola, 71: 307-320.