New Caledonian crows rapidly solve a collaborative problem without cooperative cognition

Abstract

There is growing comparative evidence that the cognitive bases of cooperation are not unique to humans. However, the selective pressures that lead to the evolution of these mechanisms remain unclear. Here we show that while tool-making New Caledonian crows can produce collaborative behavior, they do not understand the causality of cooperation nor show sensitivity to inequity. Instead, the collaborative behavior produced appears to have been underpinned by the transfer of prior experience. These results suggest that a number of possible selective pressures, including tool manufacture and mobbing behaviours, have not led to the evolution of cooperative cognition in this species. They show that causal cognition can evolve in a domain specific manner-understanding the properties and flexible uses of physical tools does not necessarily enable animals to grasp that a conspecific can be used as a social tool.

Fig 1. A sequence of photos showing New Caledonian crows mobbing a raptor.

Photo credit Mick Sibley.

Fig 2. Experimental setup and apparatus used by group one.

The diagram of the box shows the cooperative apparatus. Stones dropped through the hole on the surface of the box would hit a baited central platform, causing the platform to swing downwards and release the food. The large diagram shows the setup of the box between two cages. The crow on the left (‘passer’/subject) had to pick up a stone and place it next to one of two gaps in the wire mesh divider (passing locations). The crow on the right (‘dropper’/partner) could then drop the stone into the apparatus and release food into both cages. For group two, the hole in the apparatus was on the left.

Fig 3. a & b. Mean number of stones passed on the cooperative apparatus in the social and asocial conditions.

(a) total, 20 trials (b) first trial in each social or asocial block, 5 trials. Error bars ± S.E.

Fig 4. Model-predicted probability of stone passing in relation to the total volume of food in the apparatus (Test 1b).

Crows increased their passing rate as food volume increased. Circles = equity conditions, squares = inequity conditions. Error bars = 95% confidence intervals.

Fig 5. Mean number of stones passed in an inequity test by group 2 (Test 2c).

Disadv. = Disadvantageous, Adv. = Advantageous, DF = dog-food, M = meat.