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Tuesday, October 9, 2012

Questions

You know that question — if you were on a deserted island and could only have ten books with you, or ten songs, etc., which ones would you choose?  Well, if someone told me I could only keep a blog on one topic, ravens would have to be at the top of the list.  (What would you choose?)

On 30 September, I came upon two ravens walking along the upper beach.  They were actively (and I mean actively!) digging in the sand.  In the next two photos you can see the sand flying as they scooped it with their bills and shoved it upwards and outwards.



Every now and then the ravens would pause and look into or around the pit.



And then they would very delicately pick out something with the tip of their bills.


Of course, the next question is, what were they finding?  So I went up to the same zone on the beach and looked at the pits to get a feel for their size and shape and depth.


Then I started digging.  

Eventually, I encountered these:


I think the ravens were finding and eating beach hoppers!  The amphipods were ~1 cm long and looked similar to those I wrote about on 20 March 2012 (see better photos from that post here).

Part of natural history is watching carefully and asking questions.  I had lots of questions about this behavior.  Here are some examples, straight from my field notebook:
  • Is this behavior age-dependent?  Are these juvenile birds?
  • Can the ravens see the burrow entrances of the beach hoppers, or do they randomly choose a place to dig?
  • Might this behavior be more common under foggy conditions, when other prey is less visible or less active?  (Does fog influence foraging?)
  • Fog aside, is it based on the general availability of other prey?  (When other prey are hard to locate, they'll go for beach hoppers instead?)
  • Are beach hoppers a lesser quality prey, or are they valued?
  • Does it only occur during higher tides, when the wrack line is higher on the beach?
  • Is it density-dependent?  (Does it only occur when beach hoppers are present at high densities?  When is it worth it to a raven to dig for beach hoppers?)
  • Do ravens learn this behavior by watching other ravens, or other birds?
 
What questions do you have about this behavior?

1 comment:

Anonymous said...

perhaps we need to try a beach hopper to see what it tastes like ?? c