Sequential organization of birdsong: Relationships with individual quality and fitness

Many vocalizing animals produce the discrete elements of their acoustic
signals in a specific sequential order, but we know little about the
biological relevance of this ordering. For that, we must characterize the
degree by which individuals differ in how they organize their signals
sequentially and relate these differences to variation in quality and
fitness. In this study, we fulfilled these tasks in male collared
flycatchers (Ficedula albicollis). We characterized the sequential order
of syllables with a network analysis approach and studied the consistency
of network variables on distinct time-scales (within-day, between-day, and
between-year), and assessed their relationship with such quality
indicators as age, body condition, arrival date, and fitness-related
proxies like survival to the next year and pairing success. We found that
the syllables were associated non-randomly with one another and both the
frequency differences of consecutive syllables and the number of motif
types were higher in the original than in randomized syllable sequences.
Average degree and small-worldness showed considerable among-individual
differences and decreasing repeatability with increasing time-scale.
Furthermore, we found relationships between male age and average degree
among and within individuals. Accordingly, older males produce syllable
sequences by using common syllables less often than younger individuals.
However, the network variables showed no relationship with fitness-related
variables. In conclusion, the sequential organization of birdsong has the
potential to encode individual-specific characteristics, which thus could
be used as signals in social interactions and thus potentially could be
subject to sexual selection.