Corvus vs.Corvus: raven and northwestern crow

right in front of my deck here, a small drama is being played out. No doubt this occurs, and in the same vein, almost everywhere where raven and northwestern crow co-exist, but so far I have never seen it so close up and been able it to follow it daily with such interest.

Northwestern Crow (Corvus caurinus) looks much like any other crow but differs in that it lives and forages mostly along the coast line and, in the process, has picked up some interesting habits, very similar to the feeding behaviour on land or shoreline of seagulls, although there are differences when it comes to overall diet. Unsurprising as it can't swim, so it has to make up for that somehow I guess. When it comes to picking through garbage, crow and seagull are equally efficient in exploiting that resource; mussels by both birds are picked up and dropped from a height on rock to crack them open, crow will eat the odd fish if it can get to it without swimming, but unlike seagulls also feast on insects and fruit. Both are voracious nest robbers for both eggs and chicks.

Raven here is the Common Raven (Corvus corax principalis), our north-american variant of the originally european raven. Actually there is an interesting little detail here in that this particular variety (if you like) differs from the south-central US/Californian Western Raven (C.c. sinuatus). The latter emigrated from the "Old World" probably about a million years earlier and developed separately into a distinct version from the Common Raven which crossed into North America very much later, probably via the same Bering Strait land bridge, and also probably at about the same time as the first humans crossed into North America from Asia. This puts a rather interesting perspective on "our" Raven as the discoverer or creator of "first man", which is a very strong and alive tradition amongst the Coast Salish First Nations (the PC term in Canada for north american indians), and which I find particularly fascinating and poignant as by most accounts (except the Haida of course…) that happened right here, on Squamish Nation Indian Reserve 26 near Gibsons. More about this some other time.

two northwestern crows have set up home and built or are building a nest in the rather magnificent Western Hemlock tree, right opposite my deck, in the neighbour's front yard. In fact there are a couple more nests of other crow pairs in trees further down the road. Two or three times a day, raven appears to inspect the crows' nest, whether as a local building inspector or chef to see whether dinner is about to be served I cannot determine from here, sadly, without climbing the tree, which I don't and won't. And a little ritual plays out.

raven "whooshes" in (the only way to describe that characteristic and unmistakable sound a flying raven makes) and plonks itself on top of the hydro pole about 5 m away from the hemlock and nest, makes a little bit of noise and stays there for a couple of minutes. This immediately elicits the response from the two nesting crows, start dive-bombing the raven who blissfully and entirely ignores this. After a couple of minutes the raven hops into the tree for a closer inspection of the nest while the crows aimlessly and in anticipation of the return of the raven flutter around the tree at height for a bit. No attempt is made by the crows to drive the raven away from the nest inside the tree canopy; they just wait. 

raven re-appears from the tree canopy, sets him- or herself on the hydro pole for a few seconds and the dive-bombing is resumed. Next it hops off and whooshes down the road towards the second nesting tree, dive-bombed by "my" pair all the way, but well before it gets to the second tree, “my” pair is now joined in action by the second nesting pair who sometimes, but not frequently, manage, by concerted action from above and below by all four birds now, to divert the raven away from its next stop. If not, raven enters the second tree for an inspection and the story repeats, a flight of four crows now, circling the tree waiting for it to re-appear and action to resume.

raven re-appears and on its way to tree number three but, yes, the attack flight of four is joined by the next nesting pair and.. invariably, when bombed by 6 birds in unison, raven reconsiders the merits of doing his or her inspection of tree number three and leisurely, always leisurely and never hurried, whooshes off into the distance. Only to re-appear and the whole ritual to be repeated in exactly the same manner and time frame a few hours later. 

interesting and fascinating because it shows that the only available strategy of the crows is to try and make raven change its mind before it gets to the nest and there is absolutely no "defence" if it doesn't; the nest gets plundered.

also interesting that a "discovered" nesting pair happily and haplessly, day in day out, for nearly three weeks now, makes no attempt to vary its blindingly obviously useless strategy, nor ups sticks and decides to nest somewhere else, better hidden..

even more curious, that only the third pair benefits from this strategy, by having joined forces with two "revenge"-seeking pairs, and has its nest protected. Not so the first pair who receive no help, despite the fact that the other two pairs are well aware of the presence of raven from the moment it whooshes in and settles on the hydro pole.

equally curious that the raven always follows the exact same sequence of nests and trees and perhaps fortuitous, as now the third nest stands a chance of bringing up its young.. coincidence or design? keeping ravens larder for future years stocked? If it were to reverse the sequence or randomly picks one out of three in order, none of the nests would succeed..

I could of course put numbers to it as I now have more than enough data and observations, treat it statistically and show that this is indeed a deliberate raven strategy with p=<0.05 (yes i did that..) but that requires me to enter into raven's mind and make the assumption I at least partially understand it and know what drives it... and for a mind so great and ancient, the mind of our creator or discoverer, that seems a trifle pretentious of me.

so instead I sit, watch, admire and ponder on the ritual, the drama (or is it…) being played out in front of my eyes, day after day... and enjoy it. Much more valuable.