The buffer effect and large-scale population regulation in migratory birds

Area of Science:

• Ecology
• Population Dynamics
• Ornithology

Background:

• Buffer effects occur when habitat quality varies, leading to amplified population fluctuations in poor-quality sites.
• This mechanism can regulate populations if inhabiting poor sites incurs demographic costs.

Purpose of the Study:

• To investigate the country-wide scale of buffer effects in a migratory bird population.
• To determine the consequences of buffer effects on survival and breeding arrival timing.

Main Methods:

• Studied the Icelandic black-tailed godwit (Limosa limosa islandica) population wintering in Britain.
• Analyzed population changes across different estuaries from the 1970s onwards.
• Assessed prey intake, survival rates, and arrival times in relation to population dynamics on various sites.

Main Results:

• The black-tailed godwit population increased fourfold, with varied rates across estuaries.
• Estuaries with lower initial numbers showed greater population increases.
• Birds on these high-growth, lower-quality sites had reduced prey intake, lower survival, and later arrival in Iceland.

Conclusions:

• The buffer effect significantly impacts large-scale population regulation in migratory species.
• Demographic costs associated with poor-quality sites drive population regulation.
• Buffer effects have substantial consequences for both survival and reproductive timing.