In the great majority of birds the nestling calls play a major role in parent-offspring interactions, especially as a recognition signal or a signal of need. However, early in their life cycle nestling birds undergo massive changes in their organism that are expected to influence the development of their vocalizations. In this context we investigate how the nestling call change over time, between hatching and fledgling and what call features are associated with the change over time. In a second step we address how the changes affect the discrimination between individuals at different ages. In this study we follow nine Spanish sparrow (Passer hispaniolensis) nestlings during their development individually recording their calls at 2 (n=8), 4 (n=9), 6 (n=8), 8 (n=5) and >8 (n=5) days old. Our results show that we can discriminate call produced by nestlings at different ages. A post-hoc classification correctly classified the great majority of the calls (76%). However, we were not able to identify a single call parameter responsible for the discrimination. The most discriminant parameter was the maximum frequency (7 in 9 nestlings), call duration and maximum frequency time. Against what we expected overall discrimination between individuals was highly significant in all age classes. The post-hoc classification correctly classified the great majority of the calls (73%). The most important parameters in discrimination were call duration, harmonious time, maximum and minimum frequencies. These results confirm the influence of development in the overall call features. Surprisingly, it is possible to statistically discriminate between individuals since a very early phase in their development.