Are bird song complexity and song sharing shaped by habitat structure? An information theory and statistical approach.

In songbirds, song complexity and song sharing are features of prime importance for territorial defence and mate attraction. These aspects of song may be strongly influenced by changes in social environment caused by habitat fragmentation. We tested the hypothesis that habitat fragmentation induced by human activities influences song complexity and song sharing in the skylark, a songbird with a very large repertoire and whose population recently underwent a large decline. We applied powerful mathematical and statistical tools to assess and compare song complexity and song sharing patterns of syllables and sequences of syllables in two populations: a declining population in a fragmented habitat, in which breeding areas are separated from each other by unsuitable surroundings, and a stable population in a continuous habitat. Our results show that the structure of the habitat influences song sharing, but not song complexity. Neighbouring birds shared more syllables and sequences of syllables in the fragmented habitat than in the continuous one. Habitat fragmentation seems thus to have an effect on the composition of elements in songs, but not on the number and complexity of these elements, which may be a fixed feature of song peculiar to skylarks.