Ecological constraints on extra-pair paternity in the bluethroat

Area of Science:

• Behavioral Ecology
• Evolutionary Biology
• Ornithology

Background:

• The bluethroat (Luscinia s. svecica) exhibits high sperm competition and extra-pair paternity (EPP).
• Significant annual and brood-level variation exists in EPP frequency.
• Ecological factors potentially influence this variation.

Purpose of the Study:

• To investigate if ecological factors explain annual and brood-level variation in EPP frequency.
• To assess the impact of breeding density, synchrony, temperature, and precipitation on EPP.

Main Methods:

• Analysis of ten years of data from a Norwegian bluethroat population.
• Statistical examination of relationships between ecological variables and EPP frequency.
• Focus on both annual averages and individual broods, including those with zero EPP.

Main Results:

• No significant correlation found between annual EPP levels and average annual ecological factors.
• Individual broods showed no significant effect of factors when all broods were included.
• Morning temperature significantly affected EPP frequency in broods with extra-pair offspring; lower temperatures reduced EPP.

Conclusions:

• Ecological conditions do not determine the presence of extra-pair offspring but influence its frequency when it occurs.
• Air temperature, particularly during peak female fertility, appears to be a key factor influencing EPP frequency.
• Cold weather may constrain sexual activities by forcing birds to prioritize territory maintenance early in the breeding season.