The temporal and spatial distribution of song was studied in a population of yellowhammers Emberiza citrinella. Song was most frequent during the breeding season, and within the breeding season during the fertile period of both first, second, and replacement clutches. Song activity peaked at sunrise and sunset. During the fertile period most singing took place in the central parts of the territory. Song post heights peaked during the fertile period, and more song posts lacked foliage at that time. Intrusions by male conspecifics peaked in the fertile period and in territories where males sang relatively little. Song activity and mate guarding were strongly positively correlated. Song volume was loud and song was thus apparently used in long-distance communication. These observations are in accordance with a male deterrence hypothesis, suggesting that males sing to deter neighbouring males from trespassing during the fertile period of their mate. A female attraction hypothesis, suggesting that males sing to attract neighbouring females and thereby obtain extra-pair copulations, and a female reproduction hypothesis, suggesting that males sing to start the female reproductive cycle, were partly supported by observations.