New behavioural trait adopted or rejected by observing heterospecific tutor fitness

Abstract

Animals can acquire behaviours from others, including heterospecifics, but should be discriminating in when and whom to copy. Successful individuals should be preferred as tutors, while adopting traits of poorly performing individuals should be actively avoided. Thus far it is unknown if such adaptive strategies are involved when individuals copy other species. Furthermore, rejection of traits based on tutor characteristics (negative bias) has not been shown in any non-human animal. Here we test whether a choice between two new, neutral behavioural alternatives-breeding-sites with alternative geometric symbols-is affected by observing the choice and fitness of a heterospecific tutor. A field experiment replicated in four different areas shows that the proportion of pied flycatcher females matching the choice of the tit tutor consistently increased with increasing number of offspring in the tit nest, to the extent of nearly complete prevalence in one of the areas when tit fitness was highest. Notably, all four replicates demonstrate rejection of the behaviour of lowest-fitness tutors. The results demonstrate both acquisition and avoidance of heterospecific behavioural traits, based on the perceived (lack of) tutor fitness. This has potential implications for understanding the origin, diversity and local adaptations of behavioural traits, and niche overlap/partitioning and species co-occurrence.

Figure 1.

Experimental setup. A symbol was randomly assigned to the tit nest, and the alternative symbol was attached to the adjacent empty box. These two boxes portray tutor choice, and tit territoriality prevents settling there. Two empty boxes with the alternative symbols were offered for arriving flycatchers approximately 25 m away, adjacent to each other. The two boxes fall within the small territory defended by male pied flycatchers, forcing the female to choose in which to build its nest. The tutor nest and its accompanying empty box were always visible from the flycatcher boxes. Replicate setups were at least a kilometre apart to ensure independence.

Figure 2.

Proportion of flycatcher choices matching with the portrayed tit tutor choice between two novel symbols (circle or triangle attached at nest-box entrance), as a function of the number of offspring in the heterospecific tutor nest. Lines show logistic regression fits at observed values of offspring number. Solid lines with open squares are for the three Finnish study areas (from top to bottom: OU08, JY07 and JY08); the type of symbol chosen by the tutor had negligible effect and is not included in the fits, but the effects of study area are included to show similarity of slope despite moderately (but non-significantly) differing constants. Dashed lines with black symbols (triangle and circle) are for the one Latvian study area (DA09); the fit includes the effect of the type of symbol (triangle or circle) attached on the tit tutor nest and responses are shown separately for the symbol types, to show significant flycatcher bias towards the triangle. However, the response slopes are very similar for triangles and circles.

Figure 3.

The choices of pied flycatcher females in the four study areas (a) Daugavpils 2009; (b) Jyväskylä 2007; (c) Jyväskylä 2008 and (d) Oulu 2008. White bars denote number of pied flycatcher nests in the nestboxes with a symbol matching the symbol on the tit tutor's nest-box, black bars denote nests in the nestboxes with an opposite symbol. X-axis shows the number of offspring in the tit tutor nest on the day when presence of nest material indicated flycatcher choice.