Variable social organisation and breeding system of a social parrot revealed by genetic analysis

Social organisation and contributions to reproduction vary widely within
and between species that breed in groups. Such variation often arises from
the process of group formation, which drives patterns of relatedness and
hence the degree of social conflict and cooperation between group members.
Using field observations and molecular genetics, we investigated breeding
behaviour in an urban population of the highly social Monk Parakeet,
Myiopsitta monachus, to address two objectives. First, we investigated
breeding group frequency, composition and formation, finding that 19% of
breeding units were cooperative groups, ranging in size from 3-5 birds,
the remainder being pairs (81%). Group composition was variable with
multi-male, multi-female and multi-male-female groups. Relatedness in
breeding groups also varied with many containing kin, but some groups
containing only non-kin. This variation reflected alternative routes to
group formation, including offspring retention by pairs, sibling
coalitions and aggregation of unrelated individuals. Secondly, we
investigated productivity, reproductive investment and patterns of
parentage in relation to the size of breeding units. Productivity did not
differ significantly between pairs and groups. We detected extra-pair
paternity in 27% of broods raised by pairs, and parentage shared among
more than two members of most breeding groups, with joint-nesting by
females detected in multi-female groups.