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IF THE manic twittering of your neighbourhood birds is driving you mad, try
moving to an area with shorter trees. The speed at which some birds sing depends
on how high they perch, with each song perfectly designed to be heard clearly at
a particular height.

Erwin Nemeth at the Konrad Lorenz Institute for Comparative
Ethology in Vienna and his colleagues studied five species of Venezuelan ant
bird living in the Surumoni rainforest. Different species habitually perch at
different heights, and the team found that the songs vary in tempo—birds
living closest to the ground sing the slowest.

The researchers played recordings of each species’ song at each perching
height and measured sound quality, including how fast it faded and how well it
could be heard above background noise. Each song was heard most clearly at the
natural perching height of the species. Nemeth says ground-level birds sing
slowly to avoid the garbling that occurs when sound bounces off trees. But the
calls of birds up in the canopy travel unhindered, so they sing fast runs of
notes to cram in more information.