Nest Material Shapes Eggs Bacterial Environment.

Area of Science:

• Ecology
• Animal Behavior
• Microbiology

Background:

• Pathogenic microorganisms exert selective pressures on hosts, leading to the evolution of antimicrobial defenses.
• Aromatic plants and feathers are hypothesized to act as antimicrobial nest materials, but experimental evidence is limited.
• Nest building is a costly behavior, suggesting adaptive strategies based on environmental microbial risks.

Purpose of the Study:

• To experimentally investigate the antimicrobial effects of feathers and aromatic plants on eggshell bacterial loads in spotless starlings (Sturnus unicolor).
• To assess the influence of incubation activity and environmental bacterial density on the efficacy of these nest materials.
• To differentiate between antimicrobial functions and potential sexual roles of nest materials.

Main Methods:

• Two-year field experiment using natural and artificial spotless starling nests with varying linings (feathers, plants).
• Quantification of bacterial groups (mesophilic bacteria, Enterobacteriaceae, Staphylococcus, Enterococcus) on eggshells.
• Experimental manipulation of egg bacterial density and nest conditions (with/without incubation).

Main Results:

• Feathers and plants significantly reduced eggshell bacterial load, particularly in artificial nests without incubation.
• Antimicrobial effects were more pronounced in years/locations with higher initial eggshell bacterial density.
• Incubation activity appeared to counteract the antimicrobial benefits of nest materials, suggesting an active role against colonization.

Conclusions:

• Feathers and aromatic plants possess antimicrobial properties that contribute to eggshell protection in bird nests.
• The effectiveness of these nest materials is modulated by environmental bacterial pressure and incubation.
• Birds may adjust nest-building investments based on perceived microbial risks during incubation.