Nest-relief behaviors and usage of call types in the Kentish plover (Charadrius alexandrinus)

In bi-parental species, breeding pairs cooperate to regulate incubation duration through nest-relief behavior, using vocal signals to communicate when exchanging incubation duties. To better understand this behavior, two important questions are (1) which vocalizations are mainly used with nest-relief behavior and (2) which parent initiates nest relief using these vocal signals. In this study, we examined the vocalizations and behaviors of incubating pairs of Kentish plovers ( Charadrius alexandrinus ). We categorized nest-relief calls and investigated the major call types used when initiating nest relief and when the partner responded and analyzed the number of initiating calls by sex and behavioral role (relieving or incubating). We observed that they used four call types: type A (“tit”), type B (“pee”), type B-long (“PEEjurrr”), and type C (“rrooh”). Call type C, which is known as an agonistic call, was the most used nest-relief call. Additionally, we found that relieving individuals produced initiating calls more frequently than incubating individuals, but there were no sex differences. These results suggest that Kentish plovers make use of specific call types during nest relief, and we discuss the possibility of relationships between nest-relief calls and coordinative behavior when dividing labor in a parental pair.