Personality, recognition cues, and nest sanitation in obligate avian brood parasitism: what do we know and what comes next?

Obligate avian brood parasitism (ABP) refers to a special kind of breeding strategy observed in birds in which some species (parasites) do not invest parental care in their offspring but rather impose this duty on other species (hosts; Soler 2014). Such special breeding behavior has received attention since ancient times. For example, “The Book of Poetry” (11th–6th century B.C.) recorded the parasitic behavior of cuckoos in China. Only 1% of bird species have evolved to engage in such behavior, and the cost incurred by the hosts has triggered a variety of anti-parasitic defenses in the latter (Yang et al. 2019), leading to textbook coevolution between parasitic and antiparasitic adaptations between the parasites and hosts (Davies 2011). Both the parasitic and anti-parasitic behaviors vary across species, populations, and individuals (Davies 2000; Yang et al. 2010; 2015a, 2015b, 2015c, 2015d), and they change over time and individual age, experience (Moksnes et al. 1993, 2000; Moskát et al. 2014), and possibly personality (Avilés and Parejo 2011). Although ABP has been the subject of numerous studies since Darwin’s time, the personalities of the parasites and hosts have not been taken into account much in previous studies. As to the recognition cues, which are used by the hosts to discriminate parasites, have received more studies, but mostly focused on egg recognition that there is still a dearth of exploration to the nestling recognition (Wang et al. 2020). Furthermore, nest sanitation, a behavior that is similar in pattern to egg rejection, was proposed to be a pre-adaptation of the latter in hosts (Rothstein 1975); however, the conclusions from previous studies were mixed. In this special column of Current Zoology, we provide empirical data and theoretical discussion of these research topics. Here I provide a brief introduction of the articles in this special column, and encourage future studies by providing perspective on some research gaps.