Carrion crows dunk their toast

I had the chance of watching a Carrion Crow dipping bread in a puddle this morning. The crow deliberately walked towards me holding a piece of bread in its bill as it approached the water. It was obviously so preoccupied with the task that took no notice of me taking the camera clumsily from inside my backpack. I stayed still and avoided eye contact while the crow carefully placed the bread on the edge of the puddle and nibbled a few bits. Immediately after, it decided to walk around the puddle turning a few leaves and stones over - even a leaf that was, literally, almost touching my feet. After this, the crow run to the bread across the puddle and ate it. You can see its gular pouch filling and there is little bread left on the photo above taken at the end of the following video.

I had previously seen just once this bread-dipping behaviour. While feeding the birds in the park with my daughter, the pigeons kept stuffing themselves on the bread. The whole chunks of bread inside the pigeons crops made their necks stick out funnily. A crow turned up, fetched some bread and then walked towards the pond edge, dipping the bread and eating it while wet and soft. Today's crow was more interesting, as it waited for a while before returning to the bread, as if allowing it to soften.

  Crows are amongst the few animals able to learn to wait to receive a reward. Dunking bread is equivalent to cooking: there is some food preparation involving costs: time, effort and potential food loss (another crow might come while you wait and steal your food) before you can enjoy an easier to eat food. Overcoming the impulse to eat the raw food straight away is a prerequisite for cooking. Young children are incapable of the self-control involved in having to wait for a reward - they are naturally impatient - and the ability develops slowly, but great apes are also able to control an impulse to eat a reward in exchange of delayed rewards of higher quantity or quality. Crows join humans and great apes in being able to delay gratification. Crows might be predisposed to waiting for a reward as they do routinely hoard food for later - leaner - times. Valerie Dufour and colleagues carried out experiments on captive Carrion Crows and Ravens that demonstrated delayed gratification. They showed the crow a desirable item (grapes, cheese or sausage) but gave them a less desirable food (bread). Then, if the crow waited for a length of time and returned the bread, they were given the tasty reward. The crows - at least some of them - were able to wait up to five minutes to exchange the bread to obtain the desirable reward. They were also more willing to wait longer for their favourite item (usually sausage).

Figure 1. General capacity to wait: percentage of successful exchanges according to the length of waiting period for individual Carrion Crows (from Dufour et al 2011).

  In the video sequence above, the crow carries out a series of activities before eating it (drink water, lift a few leaves and turn stones). This is reminiscent of displacement activities to alleviate a frustration. The experimental Carrion Crows, especially those waiting for longer, also carried out such displacement activities while waiting for the desirable reward (placing the bread on the ground, pacing up and down their cages, or hiding it repeatedly)(you can watch some videos of the experiments here).

More information

Dufour, V., Wascher, C., Braun, A., Miller, R., & Bugnyar, T. (2011). Corvids can decide if a future exchange is worth waiting for Biology Letters, 8 (2), 201-204 DOI: 10.1098/rsbl.2011.0726