The study species
The study species
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The Iberian magpie (Cyanopica cooki) is a small colonial corvid (body mass 70 g), with a cooperative socially monogamous breeding system. Each year, it shows helping behaviour in variable degree depending on the environmental conditions. Helpers (i.e. individuals cooperating in provisioning offspring and removing faecal sacs with the breeding pair) reported in the study area were mainly males, but both juvenile and adult birds could become helpers. There are two types of helpers in the Iberian magpie: a) First option helpers are those that do not initiate their own breeding in that season and only assist others’ nest. They are typically juveniles that help others before starting their own reproduction. b) Second option helpers are typically adult birds that attempted their own breeding but help others after their own nest fails. In addition, individuals easily shift between breeder and helper roles, specially for second option helpers.
This species is a good model for studying the contribution of helpers because pairs do not differ in territory quality: all birds can forage in a group throughout the home range area around the breeding colony. On the other hand, Iberian magpies are single brooded; they very rarely have a second brood and whether they do is not related to the presence of helpers. Hence, helpers cannot increase the number of nesting attempts in one season.
Therefore, some of the variables involved in most cooperative breeding systems are naturally controlled in this species.