Abstract and Summary
Conspecific song was played back to freeliving territorial blackbird males to sec whether time of day, stage of the breeding cycle and number of trials with each bird influence the outcome of playback experiments and thus the predictability of responses.
Relatively few aggressive behaviour patterns (response type one) were released in the late afternoon. At this time of day the full song (response type three) was relatively frequently released. Further, aggressive behaviour patterns were more frequent before incubation started. Finally, aggressive patterns were only frequent in the first two experiments with each bird. Apparently behaviour patterns influenced by conflicting tendencies (response type two) were most frequent in the middle experiments. Full song was most frequent in the last experiments. The changes in behaviour from experiment to experiment are interpreted as due to a combination of learning and a shift in motivation. The decrease in frequency of the escape-motivated alarm “seee” is interpreted as caused by fewer chances to discover the observer.
The present study confirms that behaviour patterns of response type one are the most common patterns, their variation in frequency is less and they are more often performed in a continuous way, i.e. with relative constancy throughout the experiment. If only these behaviour patterns are quantified, response predictability is greatly improved. Response type one patterns also vary least early and in the middle of the day, and are more often performed then in a continuous way, particularly before the start of incubation and in the first two experiments with each bird. When limiting comparisons of different experiments to those performed with the above-mentioned restrictions, the predictability of response improves still more and the risk of misinterpretation is greatly reduced.