Migration strategy and divergent sexual selection on bird song

Area of Science:

• Evolutionary Biology
• Animal Behavior
• Ornithology

Background:

• Migratory birds are often assumed to face greater sexual selection than sedentary populations, evidenced by more complex songs.
• However, sexual selection pressures from male competition and female choice may not always align and can influence song evolution divergently.

Purpose of the Study:

• To investigate how sexual selection pressures from male competition and female choice differ between migratory and sedentary blackcaps (Sylvia atricapilla).
• To determine if song complexity in blackcaps correlates with migratory behavior and distinct selection pressures.

Main Methods:

• Analysis of song structure in two sedentary and two migratory populations of blackcaps.
• Differentiating song components directed towards males versus females.

Main Results:

• Migratory blackcaps exhibit longer, more complex female-directed songs, suggesting stronger female choice.
• Sedentary populations display shorter, more repetitive male-directed songs, indicative of intense male competition.
• Selection pressures from male competition and female choice operate independently across migratory behaviors.

Conclusions:

• Sexual selection intensity varies independently between migratory and sedentary bird populations.
• Shifting migratory patterns can lead to unpredictable outcomes for the evolution of sexual signals.