A comparative analysis of some life-history traits between cooperatively and non-cooperatively breeding Australian passerines

Comparative analyses were carried out for some life-history traits of cooperatively and non-cooperatively breeding Australian Corvida (i.e. old-endemic passerines). Multivariate statistical analyses at the family and genus levels revealed no significant differences between cooperative and non-cooperative breeders. A matched-pairs analysis between congeneric species showed that cooperatively breeding species lay smaller clutches than non-cooperatively breeding congenerics. Preliminary results also suggest that cooperative breeders have higher probabilities of rearing a second brood in the season and lower probabilities of survival than do non-cooperative breeders. However, the result for survival was significant in only one out of three tests. We conclude that cooperatively and non-cooperatively breeding Australian Corvida cannot be separated into distinct groups showing K- and r-selected life-history traits, respectively. Some life-history traits follow the prediction of the r-K selection model, others show evidence of co-adaptation instead, whereas still others show evidence of trade-offs.