Breeding Behaviors and Kinship in the Endangered Hawaiian Stilt (Ae'o; Himantopus mexicanus knudseni)

Understanding the genetic underpinnings of cooperative and noncooperative breeding behaviors is critical for species of conservation concern. We investigated the genetic relatedness of Hawaiian Stilts (Ae'o; Himantopus mexicanus knudseni), a threatened subspecies restricted to the Hawaiian Islands, in relation to nesting behavior, given recent behavioral observations of cooperative breeding, potential conspecific brood parasitism, and potential pairing of closely related individuals for nesting. Using RAD sequencing of blood and feather samples, we generated ~6800 SNPs for parentage and relatedness analysis. Observational data documented behaviors including cooperative incubation, helpers-at-the-nest, and potential conspecific brood parasitism, which are rarely reported in Charadriiformes. Parentage, genomic relatedness, and Bayesian phylogenetic analyses revealed instances of conspecific brood parasitism and potential extra-pair paternity. We also find evidence of inbreeding, with an overall F IS of 0.23 and close genetic similarity between some mates. Ecological constraints and limited dispersal opportunities may promote cooperative breeding, conspecific brood parasitism, and inbreeding in Hawaiian Stilts. These results underscore the importance of maintaining and restoring nesting habitat to reduce pressures that may otherwise intensify inbreeding in this recovering population but also highlight the behavioral flexibility and adaptive capacity in this species.