Aggressive behaviour affects selection on morphology by influencing settlement patterns in a passerine bird

Area of Science:

• Evolutionary Biology
• Behavioral Ecology
• Animal Behavior

Background:

• The role of behavior in driving evolutionary change is understudied due to limited empirical evidence.
• Aggressive territorial interactions can significantly alter selection pressures on individuals.

Purpose of the Study:

• To investigate the evolutionary significance of aggression in western bluebirds (Sialia mexicana).
• To determine how aggressive behavior influences individual settlement patterns and subsequent selection pressures.

Main Methods:

• Experimental manipulation of nest box density to assess male aggression and territory acquisition.
• Correlating male aggression levels with breeding habitat characteristics and morphological traits.

Main Results:

• More aggressive males secured territories with higher nest box density.
• Males sorted into open habitats (requiring agility) showed selection for longer tails and tarsi.
• Selection on these morphological traits was weaker in forested habitats.

Conclusions:

• Aggression acts as a key factor in local-scale selection by influencing where individuals settle.
• Behavioral sorting into distinct habitats can shape the evolutionary trajectory of populations.
• Territorial interactions mediated by aggression have broad implications for evolutionary processes across taxa.