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Song discrimination of neighbors and strangers by male territorial northern spotted owls (Strix occidentalis caurina)
Studies of song communication in passerine birds have supported the "dear enemy" hypothesis which states that neighboring territory owners should develop stable relationships over time to reduce energetically costly behavioral interactions. Songs and calls may provide details regarding kinship, territory boundaries, neighbor recognition, and even individual recognition. I tested the "dear enemy" hypothesis toexamine the response of male Northern Spotted Owls (Strix occidentalis caurina) to call playbacks of their neighbors and strangers as well as to calls of their neighbors in a novel location (opposite territory boundary). A bird that can discriminate between neighbor's songs and associate each with a particular location (hence the opposite boundary test) may demonstrate individual recognition. I conducted a field experiment to examine song discrimination by playing three different treatments to my subjects. Two call playback treatments (neighbor and stranger) and a control were played at the boundary that borders the territory of each tested individual and its neighbor, with a third treatment on the opposite boundary (opposite neighbor). I tested three response variables 1) latency to first response, 2) number of calls given within the test period, and 3) average time between calls. I used a crossover experimental design where I blocked for possible sources of variation such as season and time of day. Of the three response variables, latency showed a significant treatment effect with owls responding sooner to strangers than to neighbors. This supported the "dear enemy" hypothesis. The opposite neighbor treatment produced unpredicted results from tested individuals in that their first response took the greatest amount of time. However, once they responded it was with the most intensity. The delayed reaction results may suggest a confusion effect or delayed recognition. Time of year and order of treatments also influenced the responses. Such sources of variation can play a large role in the outcomes of avian playback experiments and should be considered in future experimental designs for any playback studies.