Reference
John P. Dittami, Joan Wozniak, Gabriele Gänshirt, Michael Hall, Eberhard Gwinner (1985/86): Effects of Females and Nestboxes on the Reproductive Condition of Male European Starlings, Sturnus vulgaris, during the Breeding Cycle – Vogelwarte - Zeitschrift für Vogelkunde – 33_1985: 226 - 231.