Fission-fusion dynamics over large distances in raven non-breeders

Abstract

The influence of fission-fusion dynamics, i.e., temporal variation in group size and composition, on social complexity has been studied in large-brained mammals that rely on social bonds. Little is known about birds, even though some species like ravens have recently received attention for their socio-cognitive skills and use of social bonds. While raven breeders defend territories year-round, non-breeders roam through large areas and form groups at food sources or night roosts. We here examined the fission-fusion patterns of non-breeding ravens over years, investigating whether birds meet repeatedly either at the same or at different locations. We combined four large datasets: presence-absence observations from two study sites (Austria, Italy) and GPS-tracking of ravens across two study areas (Austria, France). As expected, we found a highly dynamic system in which individuals with long phases of temporary settlement had a high probability of meeting others. Although GPS-tagged ravens spread out over thousands of square kilometres, we found repeated associations between almost half of the possible combinations at different locations. Such a system makes repeated interactions between individuals at different sites possible and likely. High fission-fusion dynamics may thus not hinder but shape the social complexity of ravens and, possibly, other long-term bonded birds.

Decision time modulates social foraging success in wild common ravens, Corvus corax

“…The study took place at Cumberland Wildpark, in Grünau im Almtal, Austria, where common ravens forage at the enclosures of zoo animals all year round in groups of 20–80 birds. These foraging groups are not stable units: while some individuals use the park regularly over several months and even years, others just visit from time to time (Braun et al, ; Loretto et al, ). The presence and social interactions of these ravens are monitored on a daily basis as part of a long‐term programme.…”

“…Common ravens Corvus corax are scavengers, which form temporary foraging groups at food bonanzas such as carcasses or kills (Heinrich, ) as well as at garbage dumps and game parks (Loretto, Schuster, & Bugnyar, ); accordingly, the size and composition of foraging groups vary across days (Braun, Walsdorff, Fraser, & Bugnyar, ; Heinrich, Kaye, Knight, & Schaumburg, ). However, ravens also show substantial individual variation in their local preferences and fission‐fusion dynamics, respectively, with some birds encountering each other regularly (over up to several years) at the foraging site or repeatedly at different sites (Loretto et al, ). Furthermore, ravens tend to form affiliative social relationships already at the non‐breeder state, which resemble primate social bonds (Fraser, Schino, & Aureli, ) and function as alliances in conflicts (Braun & Bugnyar, ; Szipl, Ringler, Spreafico, & Bugnyar, ).…”

Effect of rearing style on the development of social behaviour in young ravens (Corvus corax)

“…Furthermore, non‐breeder groups have an open character with individuals joining or leaving others on a daily basis; however, some individuals may meet regularly over months and even years at the same foraging sites or night roosts (Braun & Bugnyar, ). This variation in fission–fusion dynamics likely results in different degrees of familiarity between individuals and the necessity to regularly update social information (Loretto et al, ; see also Aureli et al, ). Thus, considering the challenges of the non‐breeder social life, we can expect the basic building blocks of ravens’ social behaviour to develop prior to the transition to non‐breeders, that is family phase.…”

Reconciliation and third‐party affiliation in carrion crows

“…Furthermore, the social structure of some bird species, notably members of the corvid family, supports the occurrence of post‐conflict behaviour (e.g., Fraser & Bugnyar, , ; Fraser, Koski, Wittig, & Aureli, ; Logan, Ostojić, & Clayton, ; Seed, Clayton, & Emery, ). The social structure of corvids is characterised by different types of social relations (e.g., pair partners, siblings, affiliates) and temporarily high fission–fusion dynamics in some species (Clayton & Emery, ; Loretto et al., ). These social matrices allow room for social interactions between various individuals especially in the non‐breeding state.…”