Data from: Social parasitism as an alternative reproductive tactic in a cooperatively breeding cuckoo

Cooperatively nesting birds are vulnerable to social parasites that lay
their eggs in host nests but provide no parental care1,2,3,4. Most
previous research has focused on the co-evolutionary arms race between
host defences and the parasites that attempt to circumvent them5,6,7,8,9,
but it remains unclear why females sometimes cooperate and sometimes
parasitize, and how parasitic tactics arise in cooperative
systems10,11,12. Here we show that cooperative and parasitic reproductive
strategies result in approximately equal fitness pay-offs in the greater
ani (Crotophaga major), a long-lived tropical cuckoo, using an 11-year
dataset and comprehensive genetic data that enable comparisons of the
life-histories of individual females. We found that most females in the
population nested cooperatively at the beginning of the breeding season;
however, of those birds that had their first nests destroyed, a minority
subsequently acted as reproductive parasites. The tendency to parasitize
was highly repeatable, which indicates individual specialization. Across
years, the fitness pay-offs of the two strategies were approximately
equal: females who never parasitized (a ‘pure cooperative’ strategy) laid
larger clutches and fledged more young from their own nests than did birds
that both nested and parasitized (a ‘mixed’ strategy). Our results suggest
that the success of parasites is constrained by reproductive trade-offs as
well as by host defences, and illustrate how cooperative and parasitic
tactics can coexist stably in the same population.