Simple Summary
Cooperative breeding, where more individuals than just those in a parental pair contribute to raising young, happens in many bird species. Most studies have investigated long-lived, sedentary species, many of which receive help to raise their brood from genetically related relatives. Additionally, however, cooperative breeding can happen infrequently in isolated pairs of short-lived, migratory species. The helpers in these cases have no indirect kinship relationships with the birds they help. Their benefits from helping can include direct genetic benefits, having sired some young in host nests, or direct behavioral benefits, such as inheriting territories in the future. In this study, I document several unique behaviors associated with infrequent helping. These include solicitation, a behavior through which male helpers may gain acceptance into host territories; defense of host territories by helper males; helpers singing when host males are absent, but not when they are present; and a single male simultaneously being a helper in four adjacent territories. Infrequent cooperative breeding most often may be found in healthy breeding populations, where most or all prime breeding territories are occupied. However, infrequent helping has not yet been studied with regard to its possible relationship with population ecology.
Abstract
Cooperative breeding, or helping behavior, has long been recognized in birds. An ignored dichotomy, however, separates the helping found in many individuals of some long-lived, sedentary species from the helping occasionally found in the territories of isolated breeding pairs of some short-lived, long-distance migrant species. Both types of helping are called “cooperative breeding” in the literature. However, recognizing a dichotomy of “frequent” versus “infrequent” cooperative breeding would help justify the study of infrequent helping as a distinct discipline. Cooperative breeding in Wilson’s Warblers is infrequent, and among the unique behaviors found during this study were (1) solicitations by helper males, which aborted host male attacks and apparently initiated territorial acceptance, (2) an absence of sexual aggression between helper males and fertile host females, (3) attacks by helper males on intruding males during host female nest building, (4) helper males singing with impunity when host males were absent from territories, but being attacked when host males were present, and (5) a single male simultaneously serving as a helper in four adjacent host territories. Infrequent helping has essentially been ignored in studies and summaries of cooperative breeding. However, recognizing and studying infrequent helping as a distinct behavioral process could reveal interactions between helping and population ecology. Thus, infrequent cooperative breeding detected in a breeding population could reveal territorial saturation and could indicate that the population is likely ecologically healthy.