Birds sang from posts 18 percent higher between 1986 and 2010

Evidence

A comparison of height at which birds select song posts, carried out in the period 1986–1989 and 2010 by Moller (2010), demonstrated that birds have increased the height at which they sing. … The average song post was 18 % higher (1.2 m on average), and this change has been observed more clearly in species singing in trees when compared with species living in shrub vegetation. — Almo Farina, Soundscape Ecology, 300