Lack of breeding site fidelity and mate fidelity in an enigmatic socially monogamous shorebird

Remating with the same partner across multiple breeding attempts has been proven a successful strategy for many monogamous breeders across taxa. In birds, especially in migratory species, former partners often reunite at the previous nesting site. As a result, being faithful to a site is closely associated with being faithful to a partner. The long-billed dowitcher, Limnodromus scolopaceus, is a short-distance migrant that breeds in socially monogamous pairs on Arctic tundra. However, unlike all other monogamous species that breed in the same habitat, dowitchers show extreme low site fidelity. In this study, we tracked the annual migratory movements of 21 breeding pairs of long-billed dowitchers in 2019/2020 using 2 g ARGOS satellite transmitters. We estimated the similarity of autumn migration trajectories and showed that former breeding pair members did not have more similar migration routes than random male-female pairs. The space use during autumn stopover and wintering, and the breeding residency area in the following summer, did not overlap between former breeding partners, except for one pair in the autumn and the winter. Mean breeding dispersal was 171 km; true site fidelity was 16.6% for males and zero for females and hence mate fidelity was zero. Our results confirm the exceptionally low site fidelity and the absence of mate fidelity in long-billed dowitchers. Selection favouring site and mate fidelity may be weak for species with mate defence polygamy and uniparental care but should be stronger in socially monogamous systems with biparental care. It remains unclear why the fitness benefits of site and mate familiarity would be smaller for long-billed dowitchers, or why the benefits of yearly flexibility in the choice of a breeding site would outweigh the costs associated with finding a new partner. Given the life history of the species, in particular the fact that former pair members rarely use the same stopover or wintering sites, breeding site fidelity is likely to be a prerequisite for mate fidelity.& COPY; 2023 The Authors. Published by Elsevier Ltd on behalf of The Association for the Study of Animal Behaviour. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).