Trait-mediated trophic cascade creates enemy-free space for nesting hummingbirds

Area of Science:

• Ecology
• Animal Behavior

Background:

• Trait-mediated trophic cascades, where predators affect nonadjacent species through behavioral changes, are crucial for community structure.
• While birds are key predators, documented examples of trait-mediated indirect effects involving them are rare.
• These ecological effects are vulnerable to environmental changes like habitat fragmentation.

Purpose of the Study:

• To investigate trait-mediated indirect effects involving bird predators in a terrestrial ecosystem.
• To demonstrate how predator presence influences the behavior of intervening species and affects other trophic levels.
• To provide a clear example of a trait-mediated trophic cascade involving avian species.

Main Methods:

• Observational study of hummingbird nesting behavior in Arizona.
• Monitoring of breeding success in relation to the presence of hawk predators.
• Behavioral observations of jay foraging patterns in response to hawk presence.

Main Results:

• Hummingbirds nesting near hawks exhibited higher breeding success.
• Jays, a predator of hummingbird nests, altered foraging behavior when hawks were present.
• The presence of hawks created an 'enemy-free' space for hummingbirds, reducing nest predation by jays.

Conclusions:

• This study provides a clear example of a trait-mediated indirect effect involving bird predators.
• The findings demonstrate how the behavior of a top predator (hawk) can indirectly benefit a prey species (hummingbird) by altering the behavior of a mesopredator (jay).
• These indirect ecological interactions are vital for understanding community dynamics and may be threatened by environmental changes.