Figure 2.

Four models (hypotheses) explaining covariance structure among agonistic behaviours assayed during laying and incubation in wild great tits. Model (a) proposes a scenario where each combination of observables and breeding stage is underpinned by a separate factor (the null model); model (b) hypothesizes a common factor (‘module’) underpinning all observables regardless of breeding context, whereas model (c) hypothesizes a separate module for each breeding context; model (d) expands upon this scenario by hypothesizing that those modules are themselves submodules influenced by a common factor.