Out of Gondwanaland; the evolutionary history of cooperative breeding and social behaviour among crows, magpies, jays and allies

Cooperative breeding is comparatively rare among birds in the mainly temperate and boreal Northern Hemisphere. Here we test if the distribution of breeding systems reflects a response to latitude by means of a phylogenetic analysis using correlates with geographical range among the corvids (crows, jays, magpies and allied groups). The corvids trace their ancestry to the predominantly cooperative ‘Corvida’ branch of oscine passerines from the Australo-Papuan region on the ancient Gondwanaland supercontinent, but we could not confirm the ancestral state of the breeding system within the family, while family cohesion may be ancestral. Initial diversification among pair-breeding taxa that are basal in the corvid phylogeny, represented by genera such as Pyrrhocorax and Dendrocitta, indicates that the corvid family in its current form could have evolved from pair-breeding ancestors only after they had escaped the Australo-Papuan shield. Within the family, cooperative breeding (alloparental care/family cohesion) is strongly correlated to latitude and its predominance in species maintaining a southerly distribution indicates a secondary evolution of cooperative breeding in the lineage leading away from the basal corvids. Multiple transitions show plasticity in the breeding system, indicating a response to latitude rather than evolutionary inertia. The evolutionary background to the loss of cooperative breeding among species with a northerly distribution is complex and differs between species, indicating a response to a variety of selection forces. Family cohesion where the offspring provide alloparental care is a main route to cooperatively breeding groups among corvids. Some corvid species lost only alloparental care, while maintaining coherent family groups. Other species lost family cohesion and, as a corollary, they also lost the behaviour where retained offspring provide alloparental care

Conspicuous eggs and colourful hypotheses: testing the role of multiple influences on avian eggshell appearance

The diversity of eggshell colours and patterning across different birds is a fascinating example of the extended avian phenotype. The avian egg's background colours range from light green/yellow to brilliant blue and intense maroon, and with the scrawling patterns comparable to the assortment of eggs found in an Easter Bunny's basket. Here we briefly introduce the diversity of eggshell appearance, its perplexingly narrow chemical basis, and clarify how the a priori assessment of assumptions and potential hypotheses can shape new eggshell research. In addition, we highlight some of the recent hypotheses developed outside the visual paradigm that has dictated the most influential hypotheses of eggshell appearance to date. Finally, we indicate priority areas for future comprehensive research on eggshells based on adaptations to ongoing changes in environmental conditions.Phillip Cassey, Golo Maurer, P. George Lovell and Daniel Hanle