Morph Composition Matters in the Gouldian Finch (Chloebia gouldiae): Involvement of Red-Headed Birds Increases Vigilance

Abstract

Animals invest in costly vigilance to detect threats. Joining groups reduces these costs, which can be further reduced in mixed-species assemblages. In colour-polymorphic species, morphs often experience different predation pressure and vary in a variety of traits. However, little is known about differences in vigilance or how group composition affects vigilance. The aim was to investigate whether higher conspicuousness increased vigilance and whether vigilance was reduced in mixed-morph groups like in mixed-species assemblages. I tested vigilance in the colour-polymorphic Gouldian Finch (Chloebia gouldiae). Same sex pairs of different age and of either pure (red-red or black-black) or mixed head colour were exposed to three contexts (familiar, changed and novel environment) and head movements were recorded. All birds reduced the frequency of head movements with increasing novelty, indicating different vigilance strategies (switching from a searching to a tracking strategy) depending on the situation. While vigilance did not differ between morphs, morph composition mattered. Black-headed pairs made fewer head movements than mixed-head colour pairs. Results indicated that conspicuousness did not affect vigilance, possibly due to existing adaptations to reduce predation risk. However, whenever red-headed birds were involved, vigilance increased either because of higher group conspicuousness or prevalence of aggression.

Is vigilance a personality trait? Plasticity is key alongside some contextual consistency

“…Sixteen of the 22 birds had taken part in a very similar vigilance experiment a year earlier with exactly the same procedure for the novel and familiar situation but a slightly different protocol for the changed situation. Instead of placing a novel object inside the cage, a novel object (toy penguin or panda bear, 15–17 cm height, respectively) mounted on a tripod was placed 40 cm away from the front wire outside the cage [ 22 ]. Experiences with the cages a year ago were unlikely to have affected responses as reactions to unfamiliar situations usually fully recover after non-exposure of three to four weeks [ 41 , 42 ].…”

“…In year two it was the star at a neutral location, whereas in year one an object was positioned outside the cage. Two objects were used in year one and the mean of the vigilance shown across the two objects was used in the analysis [ 22 ]. This analysis was done with One-Way ANOVA.…”

“…A series of models were built to test for effects of different variables and interactions. The basic model consisted of four fixed factors (situation, head colour morph, sex and age class), one covariate (partner head colour morph) and two interaction terms (head colour morph x partner head colour morph and head colour morph x sex), which is the same basic model used for analysis in the vigilance study the year before [ 22 ] except for sex being a fixed factor now rather than a covariate. Using the same basic model allows direct comparison with the new situations used in the current study.…”

“…Moreover, in ibex ( Capra sibirica ) female groups and mixed sex groups were more vigilant than male groups reflecting the higher predation in female groups and social vigilance directed towards harassing males in mixed groups [ 4 ]. Higher vigilance has also been observed in colour polymorphic species when in mixed morph groups as compared to monomorphic groups again indicating social vigilance [ 22 ].…”

“…While the two main morphs do not differ in their vigilance, group composition matters. Whenever red-headed birds are present (mixed or pure red-headed groups), vigilance is heightened compared to pure black-headed groups [ 22 ]. Moreover, vigilance was highly plastic across situations with fewer head movements the more novel a situation was [ 22 ].…”