Dove dilemma

Something has gone strangely wrong with the mourning doves that routinely nest in our back yard.

Chick, you're lookin' good!  Two healthy squabs in a hanging basket in the spring of 2012.  Both of these fledglings went on to launch successfully.

For the past several years, I have enjoyed watching these critters nest and flourish in a few of the planter baskets that hang beneath our covered patio.  There are many birds of prey that hunt within the confines of Centerpointe, so the patio is an excellent refuge for nesting birds. 

One of the chicks perched on a wind chime, on first furlough from the nest.  This pic was taken before I cleaned and painted the patio ceiling. 

Peeking out through window blinds to observe this fledgling sitting on the back of a patio chair as (s)he faces the world for the first time. 

My favorite photo to date: parent with squab peeking out from the leaves. 

I was disappointed to see the first nest of the season fail this year, but I chalked it up to a random act of nature and perhaps the abnormally cold weather we had this spring. 

But then things got curiouser:

The doves laid a second clutch a few weeks after the first one failed, and the second clutch failed, too. 

Do you see that one egg off to the side?  That was a failed egg that the mother bird apparently pushed out of the way as she laid the second clutch. 

Two failures in succession prompted me to examine what might be going wrong now, after multiple previous successes last year and in prior years.  I took down this hanging plant and examined the eggs.  There was no visible damage to any of them.

These things look like blood spots, but I have no real knowledge of these things. 

Using the handy morning sun to candle the eggs, I couldn't really see good differentiation in there, even though the parent dove(s) sat on both clutches for a couple of weeks (according to this site, mourning dove eggs should hatch in 14 to 16 days). 

My tentative conclusion is that these doves are sterile.  I don't know whether the first and second clutches were laid by the same mated pair, or a different pair.  According to this site, dove pairs mate for life and "wild doves are notorious for infertile eggs", so maybe their biological clocks have simply run out this year. 

In researching this, I did find that there is a sterilizing food product used to control the closely-related common pigeon species, but I'm unaware of any local use of this product.  Certainly I've never seen pigeons being a problem anywhere near League City (our hawks would take care of them in a jiffy even if their numbers did increase).  So my guess at this point is just infertility deriving from a normal cause.