Multi‐year partner fidelity is associated with higher annual reproductive output in a biparental subtropical shorebird

Partner fidelity is a key component of reproductive strategies in socially monogamous species, yet its adaptive value remains context dependent and poorly understood outside environments with short breeding seasons. In most bird species, partners may remain together or re‐pair between successive nesting attempts, but it remains unclear which components of reproduction are most strongly shaped by this decision. Using a six‐year dataset, we examined the consequences of partner fidelity and re‐pairing in the red‐wattled lapwing Vanellus indicus , a long‐lived, biparental shorebird breeding in a subtropical environment with an extended breeding season that allows repeated nesting within a year. Partner fidelity was more common than re‐pairing and was not primarily promoted by nest failure. Faithful pairs did not differ from re‐paired pairs in breeding performance during individual nesting attempts, including timing of nest initiation, egg size, clutch size, clutch survival or chick survival. However, annual reproductive output increased with pair duration: pairs that retained the same partner for longer initiated more clutches and produced more hatchlings per season. This pattern suggests that in long‐season environments, the main benefit of partner fidelity lies not in improving the outcome of a single nesting attempt, but in facilitating continued reproduction across successive nesting attempts, with occasional double brooding further contributing to reproductive output. Because pair duration was positively correlated with female breeding experience, the effects of multi‐year pair maintenance and accumulated individual experience could not be fully disentangled. Our findings highlight a pathway through which stable pair bonds may enhance reproductive output in systems permitting repeated within‐season breeding, and underscore the need for comparative studies across subtropical and tropical species to better understand how breeding season length shapes avian mating systems.