Crows usually only socialize with close family members, but they’re willing to branch out when importation information about food is being shared. The findings, published in Nature Communications this week, suggest that changes in the dynamics of their social networks could accelerate the flow of information – including how to use tools to exploit hidden prey.
Famously clever New Caledonian crows (Corvus moneduloides) can extract insects from holes in tree bark using small sticks, manufacture tools of various shapes from barbed leaves, and craft hooks out of forked twigs. However, "we currently have little idea how much of this information, if any, is socially or individually learned, or innate," Oxford’s James St Clair told IFLScience.
To explore how crow networks support the flow of information, St Clair and colleagues used wireless sensor technology to map interactions among a population of multi-family groups living in a forest on the west coast of Grand Terre Island, New Caledonia. The 33 free-ranging birds were fitted with 10-gram (0.35 ounce) tags that transmitted radio pulses every 20 seconds while also receiving and logging signals from nearby tags. Additionally, with 45 fixed receivers monitoring the roaming tags, the researchers ended up with detailed records of the time, proximity and duration of all crow encounters over a span of 19 days.
Then, to examine how changes in the abundance of local resources might affect network dynamics, the researchers mimicked resource gluts that naturally occur when decaying candlenut trees fall and break open – exposing the burrows of highly nutritious longhorn beetle larvae, which crows can dexterously extract with sticks (pictured right).
The majority of interactions occur between a small number of genetically-related crows or male-female bonded pairs. However, when tasty grubs are introduced, the overall connectivity of the network increases rapidly – and so do the interactions among birds who weren’t previously associated.
These interactions are highly localized. None of these changes were observed when the grubs became available halfway between neighboring territories of different multi-family groups. This expansion of local social network connectivity suggests that there are ample opportunities for information exchange, and this response to food likely facilitated the evolution, maintenance, and widespread adoption of tool use.
"If we think back to the crow that 'discovered' that tools could be used to obtain food (or to subsequent innovators that discovered new tool-use contexts or design features) and assume that the new information can be transmitted by social learning, then the social network properties become very important for whether, and how quickly, that information can spread or be lost," St Clair explained to IFLScience.
Some animals feed alone (and vigorously defend their resources), so when one individual comes up with a foraging innovation, there’s a slim chance of others observing it closely enough to learn it; that discovery likely dies with its discoverer. For animals that forage in very small groups of a couple individuals, or those who only tolerate close kin, innovation could spread quickly within the group or family – but probably not beyond it.
"A 'perfect storm' scenario occurs when animals are happy to aggregate in the way that we observed – next to multiple individuals that can be entirely unrelated," St Clair added. "This opens up lots of potential transmission pathways. Odds are, if somebody expresses a foraging behavior, somebody else will be there to observe it.”
A wild, wing-tagged New Caledonian crow wearing a backpack-mounted Encounternet proximity logger.
Images in the text used courtesy of James St Clair.