Control of territorial aggression in a changing environment

Area of Science:

• Behavioral Ecology
• Animal Behavior
• Avian Biology

Background:

• Song sparrows (Melospiza melodia morphna) in Washington State display year-round territoriality.
• Territorial defense occurs in different contexts during breeding and nonbreeding seasons.
• Previous understanding suggested a strong link between gonadal hormones and territorial behavior.

Purpose of the Study:

• To investigate the role of gonadal hormones, specifically testosterone, in mediating territorial behavior in song sparrows.
• To determine if territoriality is regulated by the same mechanisms throughout the year.
• To understand the seasonal variation in the hormonal basis of territorial defense.

Main Methods:

• Observational studies of territoriality in a sedentary song sparrow population.
• Measurement of circulating luteinizing hormone (LH) and testosterone levels.
• Hormonal manipulation experiments, including castration and testosterone level adjustments.
• Behavioral assays to quantify territorial defense and aggression.

Main Results:

• Territorial behavior during the breeding season correlates with elevated LH and testosterone.
• Identical territorial behaviors in the nonbreeding season are independent of gonadal hormones.
• Castrated males defend territories as effectively as intact males in autumn and into the breeding season.
• Testosterone manipulation suggests a role in enhancing aggression persistence, not initial activation.

Conclusions:

• The hormonal and neural mechanisms underlying territoriality in song sparrows change seasonally.
• Testosterone's primary role may be in modulating the persistence of aggression during the breeding season.
• Year-round territorial behavior is not solely driven by consistent hormonal activation.