Adaptive Site Selection Rules and Variation in Group Size of Barn Swallows: Individual Decisions Predict Population Patterns

Variation in group size is ubiquitous among socially breeding organisms. An alternative to the traditional examination of average reproductive success in groups of different sizes is to examine individual decision making by determining the cues used for site selection. Once factors used for decision...

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Bibliographic Details
Published in:The American naturalist 2004-08, Vol.164 (2), p.121-131
Main Author: Jo Safran, Rebecca
Format: Article
Language:English
Subjects:
Animal nesting
Animal populations
Animal reproduction
Animals
Barns
Biological variation
Bird nesting
Birds
Breeding
Breeding seasons
Breeding sites
Cues
Decision Making
Ecology
Female animals
Group size
Hirundo rustica
Nesting Behavior
Population Density
Population Dynamics
Reproduction
Reproductive success
Swallows
Swallows - physiology
Variance analysis
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Summary:Variation in group size is ubiquitous among socially breeding organisms. An alternative to the traditional examination of average reproductive success in groups of different sizes is to examine individual decision making by determining the cues used for site selection. Once factors used for decision making are known, one can determine whether group‐level patterns, such as group size variation, are emergent properties of individual‐level decision rules. The advantage of this alternative approach is that it can explain the distribution of group sizes rather than just the occurrence of optimal group sizes. Using barn swallows, I tested, but did not support, the hypothesis that individuals settle at sites based on the previous success of conspecifics (i.e., performance‐based conspecific attraction). Instead, I demonstrate that an adaptive site selection decision rule—to breed where it is possible to reuse previously constructed nests—predicts 83% of the variation in the number of breeding pairs at a site. Furthermore, experimental nest removals demonstrated that settlement decisions are also strongly influenced by site familiarity. I discuss the interaction of the cue‐based site selection rule with the occurrence of site fidelity and how, more generally, a consideration of individual‐level decision rules can improve our understanding of variation in many social behaviors.
ISSN:0003-0147
1537-5323
DOI:10.1086/422198