The question of why hens do not appear upset when their eggs are collected can be explained through biology, animal behavior, and the effects of domestication:

1. Biological and Cognitive Limitations

  • No concept of "ownership": Hens lack the cognitive ability to perceive eggs as "offspring" or "property." Unfertilized eggs (common in commercial farming) are biologically akin to metabolic byproducts (like menstrual cycles in humans), not potential offspring.
  • Brooding behavior is hormone-dependent: Protective instincts are triggered only during incubation, when hormonal changes (e.g., increased prolactin) drive hens to sit on eggs. If eggs are removed before this phase, hens show no attachment.

2. Domestication and Selective Breeding

  • Weakened maternal instincts: Over thousands of years, humans selectively bred hens for high egg production and reduced broodiness (the urge to incubate eggs). Modern commercial breeds (e.g., white leghorns) rarely exhibit protective behavior toward eggs.
  • Farming practices: Industrial systems use automated egg collection (e.g., roll-away nest boxes) to minimize contact between hens and eggs, preventing attachment.

3. Evolutionary Survival Strategies

  • Energy efficiency: In the wild, protecting every egg is energetically costly. Evolution favors hens that prioritize survival and continuous egg-laying over guarding unfertilized eggs.
  • Adaptation to predation: Wild ancestors (e.g., red junglefowl) may abandon eggs to avoid attracting predators, a trait retained in domesticated hens.

4. Exceptions: When Do Hens Protect Eggs?

  • During incubation: If a hen enters a brooding phase (triggered by hormones and environmental cues), it will aggressively defend eggs. However, commercial farms suppress broodiness to maximize egg production.
  • Heritage breeds: Some traditional breeds (e.g., Silkie chickens) retain stronger maternal instincts, but these are exceptions in modern farming.

Key Takeaway

Hens do not react to egg removal because:

  • Biologically, eggs are not perceived as "offspring" unless incubation begins.
  • Domestication has prioritized egg production over maternal behavior.
  • Evolutionary strategies favor energy efficiency over guarding unfertilized eggs.

This behavior reflects a blend of natural adaptation and human-driven selection, optimized for survival and agricultural efficiency.