Unravelling a mystery in a woodpecker’s cavity

When photographer, Peggy Honda, recently sent us this photo of a Downy nestling we found it startling!  Look closely!  The countless specks on the tree and inside the cavity are ants! Naturally we became anxious.  Earlier photos Peggy sent us confirm that the ants were not present when their parents first occupied the cavity (at least not to this degree).  Would the young family survive the infestation in their California tree-hole home?

Indeed they did, as Peggy later documented with this video.

But, we’ve been scratching our heads and searching for answers eve r since.  Why didn’t the chicks appear impacted by the ants?  Woodpeckers are insectivores, so did the ants become a ready supply of protein?   Could the ants have been in the cavity to benefit from the birds in some other way?  Here is what we found.

It would have been ideal to be able to identify the ant species, but we were unable to do so.  We did learn of a native ant present in Southern California and known to occupy dead trees that eats bird droppings!  A kind of ah ha moment.  There’s no proof, of course, that our anonymous ants did so in this case.  Though the droppings pose one plausible explanation,  we are further unsettled by the fact that the ant infestation did appear to lessen as the birds matured.  Did the cavity contain a dead chick?  Did the ants perform a helpful service?

The nest was not observed sufficiently closely to note whether the Downy parents fed these ants to their young.  Peggy recorded several deliveries of other prey.  Here’s one such occasion.  Do note the parent’s apparent lack of interest in the traffic of ants during this feeding.

28 of Insects and Widlife, by John L Capinera, we found the answer to be about 16.5%.  But Capinera also suggests that not all ants are problematic to birds.  Apparently the ant species, their quantity, and time of year play an important role.  There are six highly invasive species that are dangerous, he says.  Among those he mentioned, at least two appear to be present in our region:  The Argentine, and a fire ant.

Would good feather hygiene have helped?  Like all birds, downy woodpeckers preen  regularly and also shake themselves to dislodge insects.  Parents perform this task for their young until they are old enough to do it themselves.  It’s probably safe to conclude that good overall parenting contributed to the family’s success.  But while we still sit on the edge of fascination and bewilderment, we feel like cotton candy seeing images of the two youngsters just out of their ant-infested cavity!  And we thank Peggy Honda for documenting this intriguing nesting event.


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