Conclusions
Essentially, the answer to our question is a no yet yes. Latitude does not have a direct effect on the bandwidth, trill rate, and length of the male House Wren's song. However, the underlying theory is not wrong. Closer examination of the switch model shows that the higher up in latitude, the sooner the song switches from introductory to terminal. What does this mean?
To answer this, we must dig a little deeper into the two parts of the song, specifically the terminal song. The second half of the House Wren's song is much more technically challenging and energy- demanding than the introductory part. So if the birds in higher latitudes are switching their songs earlier, then they must have more energy than their lower latitude counterparts.
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Then there was also correlation between latitude and terminal song duration. This means that the higher up in latitude, the sooner the song switches from introductory to terminal, and the more energy a male must use to produce its song.
We also found that terminal song duration changes with year at a higher rate in the temperate zones. It may be that House Wren populations are responding to evolutionary or sexual pressure spurred on by climate change, or it could simply be genetic drift, which would alter terminal song duration over time by chance.