Assortative pairing for boldness and consequences for reproductive success in Montagu’s harrier

Abstract

Behavioural combination within pairs depending on personality and plasticity might influence reproductive success. However, studies testing this hypothesis are rare, especially in the case of monogamous species with bi-parental care in which the sexes exhibit different behavioural roles. In this study, we investigated the pairing patterns for both boldness and boldness plasticity in Montagu’s harriers (Circus pygargus), a species with sex-specific care, and the consequences for their reproductive success. We measured individual boldness and plasticity for both sexes, and we assessed the pairing pattern in the Montagu’s harrier population for these two traits. We calculated four indices to characterize the behavioural association within pairs: pair boldness, boldness similarity within pairs, pair plasticity and plasticity similarity within pairs. The relationship between the behaviour of the parents and the reproductive success was then tested through these four indices. We found a pattern of assortative pairing based on both boldness and plasticity in the Montagu’s harrier population. Within-pair similarity of plasticity had a significant effect on the reproductive success, which was higher for less similar pairs than for more similar pairs. Our results question the origin of this pairing pattern and suggest that ecological constraint and not sexual selection could be the major driver.

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“…The different distribution of boldness types influenced by the building density may have evolutionary implications for the Montagu's harrier population. A previous study in the same population showed a positive assortative pairing according to boldness (Rabdeau, Badenhausser, et al., 2021). However, no fitness benefit was detected from this pairing pattern, suggesting that it probably results from ecological constraints rather than only sexual selection.…”