Diet composition and diversity does not explain fewer, smaller urban nestlings

Area of Science:

• Ecology
• Urban Ecology
• Animal Behavior

Background:

• Urban environments often negatively impact wildlife reproductive success compared to rural areas.
• Dietary factors, prey availability, and seasonal changes can influence offspring development and survival in modified habitats.

Purpose of the Study:

• To investigate how habitat (urban vs. rural) and breeding date affect house wren (Troglodytes aedon) nestling body condition and survival.
• To determine if diet composition explains observed differences in nestling fitness between urban and rural populations.

Main Methods:

• Monitoring of urban and rural house wren populations breeding in nest boxes.
• Analysis of clutch size, nestling survivorship, and body condition variation by habitat and date.
• DNA metabarcoding of fecal samples to characterize nestling diets.

Main Results:

• Urban house wren broods had fewer and smaller nestlings, indicating reduced fitness.
• Nestling survival decreased with advancing breeding season, particularly in urban areas.
• Nestling diets were similar between urban and rural sites and did not correlate with body condition differences.

Conclusions:

• Habitat and breeding date significantly impact house wren nestling fitness, with urbanization posing a distinct challenge.
• While diet composition was similar, seasonal dietary shifts occurred, becoming less diverse.
• Factors beyond diet, potentially prey quantity or quality, contribute to fitness disparities between urban and rural house wrens.