Reproductive tactics under severe egg predation: an eider's dilemma

Area of Science:

• Behavioral Ecology
• Avian Reproduction

Background:

• Parental defense strategies in birds can impact offspring survival but may incur costs.
• Egg predation is a significant threat, particularly early in the nesting phase for some species like the common eider.
• The common eider exhibits unique nesting behaviors compared to other waterfowl.

Purpose of the Study:

• To test the hypothesis that early and continuous nest attendance by female common eiders is an adaptation to reduce egg predation.
• To evaluate alternative hypotheses for reduced predation later in the nesting period, including vulnerable nest loss and seasonal changes in predation risk.

Main Methods:

• Analyzing egg predation rates at different stages of the common eider nesting sequence.
• Comparing predation rates between nests with early attendance and those without.
• Assessing the impact of nest attendance on clutch survival and clutch size.

Main Results:

• Predation rates at the one-egg stage and later stages were analyzed to test hypotheses.
• The study refuted alternative hypotheses suggesting early nest failure or seasonal decreases in predation risk.
• Early nest attendance by female eiders significantly increases clutch survival, particularly for larger clutches.

Conclusions:

• Early and permanent nest attendance from the second or third egg is a likely adaptation for reducing egg predation in common eiders.
• This parental defense strategy enhances clutch survival by an estimated 20% for four-egg clutches and 35% for five-egg clutches.
• The benefit of increased egg survival may come at the cost of a smaller clutch size for nesting eiders.