Beschreibung:
<p>Individual song rates for territorial Willow Warbler males were monitored. The song rate means varied between males but did not differ much from day to day. After monitoring, the males were captured and removed and new males could establish in the empty territories. Song rates of the replacement males were then monitored. Territories that originally had been occupied by males with high song rates now became occupied by males who also got high ranking song rates. The results from the replacement experiments indicate that extrinsic factors connected to the territory are important in determining a male's song rate.</p>