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Friday, August 28, 2015

All in the family

Eric called to say that he was seeing some young birds outside of his office.  Luckily, they were still in view by the time I got there.  Here's my first photo:



And then I captured two in one view:


This was my first close look at juvenile Western Bluebirds (Sialia mexicana).

Eric had noticed that these juveniles were being fed.  So I kept watching, and sure enough we saw the juveniles begging.  Here is one example:



And then another example (below).  This time the bird on the right is bringing food (just barely visible in its bill).



I was a little confused when we were watching this behavior.  The juveniles were begging and receiving food from birds that didn't look like adults.

I kept watching, and then saw this bird (on the left) come in to feed one of the juveniles:


The birds were moving quickly, but the blue on the neck and rusty color on the breast looked more like an adult...but then again, not quite right.  When I downloaded the photos I could see yellow at the gape (the base of the bill).  The bird on the left was not an adult it was also a juvenile, although an older individual.  The younger juveniles were being fed by older juveniles!

So then I had to look up information about cooperative breeding in bluebirds.  In turns out that it's very rare in Eastern Bluebirds, but a bit more common in Western Bluebirds.  [For example, in one study, 7.4% of Western Bluebird pairs at the Hastings Reservation (in Carmel, California) had helpers.]

The "helpers" can be either adults or juveniles.  In this case, they were juveniles.  When this happens, the older juveniles are most often helping their parents feed a later brood.  (Western Bluebirds can have up to three broods in one season.)

P.S.  To see pictures of adult Western Bluebirds, see the post from 12 December 2013.

P.P.S.  If you'd like to learn more about cooperative breeding in Western Bluebirds, check out this paper:


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