Same species, different risks: predation shapes hormonal profiles in a breeding sea duck, the common eider

Area of Science:

• Wildlife ecology
• Animal behavior
• Physiological ecology

Background:

• Prey species often perceive humans as predators, eliciting antipredator responses.
• Human presence may also deter predators, creating a 'scarecrow effect' that reduces predation risk for prey.
• Life-history theory predicts reduced perceived risk may increase reproductive investment.

Purpose of the Study:

• To investigate the impact of the human 'scarecrow effect' on prey's perceived predation risk and reproductive investment.
• To assess hormonal markers related to energy expenditure, stress, and parental effort in common eiders under varying human disturbance and predation risk.
• To determine if reduced predation risk due to human presence affects hormonal profiles and parental effort.

Main Methods:

• Monitoring hormonal markers (corticosterone, triiodothyronine, thyroxine, prolactin) in two common eider colonies with contrasting human disturbance and predation risk levels.
• Measuring baseline and stress-induced corticosterone to assess energy expenditure and acute stress response.
• Measuring baseline prolactin as a proxy for parental effort.

Main Results:

• Eiders in high-predation colonies showed higher baseline corticosterone and triiodothyronine, indicating greater energy expenditure.
• Stress-induced corticosterone levels were similar across colonies, suggesting maintained sensitivity to acute stressors.
• Eiders in high-disturbance (low-predation) colonies exhibited higher baseline prolactin, indicating increased parental effort.

Conclusions:

• The human 'scarecrow effect' can reduce perceived predation risk in prey species.
• This reduced risk does not necessarily diminish the prey's sensitivity to acute stressors.
• The 'scarecrow effect' is associated with increased reproductive investment, supporting life-history predictions.