Subtle differences in family size mediate object play in young ravens (Corvus corax)

The social environment at upbringing shapes the developmental trajectories of offspring behaviour and competences in various species. Surprisingly, little is known about how slight variations in early social environments, such as differences in sibling numbers, affect these trajectories. Common ravens undergo an impressive socio-cognitive development post-fledging, engaging in various forms of play. We investigate the influence of (manipulated) family size on object-directed behaviours of juvenile ravens, testing the prediction that larger family size would foster more object play at standardised playgrounds. Contrary to our prediction, family size does not affect the individuals' access to objects and amount of play; however, offspring from small families are more often together at the playground and show more and selective interest in others' object manipulations than offspring from large families. Our findings indicate that even slight differences in family size - within natural range - can mediate juveniles' opportunities to interact, play, and develop their social repertoire.