Antagonism...

The South Meadow at Discovery Park in Seattle was alive with avian activity today.  Small flocks of House Finches flitted from tree to tree.  Two Anna’s Hummingbirds engaged in aerial combat as they argued over territorial matters.  Song Sparrows sang from low perches and robins foraged in the wide expanses of grass.  As interesting as all of this business was, it was overshadowed by the boisterous presence of a large contingent of excited crows.

The sun was shining down on the meadow and had warmed the ground to the point at
which the resident ant population began to stir.  The 50 or more crows that were present in the trees scattered about the meadow were taking turns flying down to the ground in smaller groups. These “mini-murders” were giving the ants some unwanted home modification assistance, poking and prodding the ant mounds with their bills and generally making a mess of them.  The unfortunate ants that were responding to the attack on their colony were either being eaten or duped into assisting the attacking crows with their personal hygiene.

It has been hypothesized that crows and some other bird species intentionally rile up anthills to use the unwitting ants as a sort of anti-parasitic treatment.  When angry ants bite, they release formic acid, which you can imagine is not a very pleasant substance.  Since the birds’ feathers are dead tissue like our fingernails, the ants don’t cause them any pain when they latch onto their feathers and release the acid; However, the mites and lice that often live on bird’s feathers are encouraged to take up residence elsewhere when they suddenly find that their home has been acidified. 

This theory of bird/ant interaction certainly seemed to fit with what I was seeing today at the park.   Although the crows were definitely eating some of the ants, they were also lying down on the stirred up anthills and spreading their wings out on the ground as if to welcome the little feather-biters aboard.  When I have witnessed this behavior in the past, I have even seen the ants clinging furiously to the crow’s wing feathers after the birds flew back up to a perch in a nearby tree.

Whatever the true extent of the relationship between crows and ants, their interactions are fascinating to observe.  These “anting parties” are clearly significant social events for the birds.  Their jovial demeanor as they poke and prod the ant colonial stands out in stark contrast to the quiet desperation of the defending ants.