Thanks.  I don't have any survey data either.  Just backyard (farm) observations.  Have you noticed any changes in other species and do you have any ideas about what is causing such a wide-spread reduction in the pigeons?

What you describe sounds very similar to what we witnessed in portugal about 15-20 years ago. The Eurasian collared doves exploded in numbers especially in areas around sites with easy access to food, such as grain silos. Since then the increase I think, slowed down, but they are increasingly widespread over the all country and it is still unclear if they have any impact on native turttle dove (which are declining very fast due to a number of reasons) or pigeons.

In India we have more pigeons then doves. Almost all places are full of pigeons, specially historical monuments. Doves are less common in comparison of pigeons and as per my view they prefer open areas or outskirts. One of reason for increased pigeon population is religious feeding of birds.

Although Im no ornithologist, I`ve had the chance to work with birds a little. As allready mentioned, Eurasian collar doves (Streptopeyla decaocto) have been invading all across Mexico. I have about 10 dwelling in one of my trees, it began with a couple 3 years ago. There`s one of my fellow posgraduate students actually doing research on the subject. If we go back a little bit further, I`ve seen changes in community here in Xalapa where I live with more tropical species becoming more common (most likely due to climate change), expanding their distribution or augmenting in number. In Mexico city I´ve noticed more mexican sparrows (Carpodacus mexicanus) than on previous years, gaining on the inglish sparrows.  So I could say...yea, there`s been changes in the bird  communities in recent times for sure.

The Breeding Bird Survey website might help contextualize your observations.

You can look at trend estimates for any number of species in a particular state, region, or across the entire survey area.  It seems a little wonky right now (some links are broken which is not typically the case) but it's a great resource for people interested in knowing whether what they are seeing in their backyard is occurring more generally.

http://www.mbr-pwrc.usgs.gov/bbs/bbs.html

In Ecuador Columba livia Rock Pigeon have increased in number, only in urban areas, and is evident the decline of native Zenaida auriculata Eared Dove. I have not observed aggressive interactions, but Zenaida auriculata is more frightened when approaching feeds, It always eats not very close to Columba livia.

Another species I have seen, has reduced its presence in my city, Quito, is the resident Pygochelidon cyanoleuca Blue-and-white Swallow; and I have not seen in flocks of 10 or more individuals flying through the city, which was usual about 10 years ago, now occasionally see a few individuals but only in parks.

birds population is declining in terms of density and diversity in india. I enclosing one of my paper on this aspect.

In the Canary Islands we have had in the last decades an important (natural) invasion of Eurasian Collared Dove (Streptopelia decaocto), and also, in a lesser extent, of Laughing Dove (S. senegalensis). Both species have colonized all the islands and they are spreading fast. Fortunately, populations of European Turtle Dove (S. turtur) are significant yet, and it's possible this last species has no suffered such invasion of the other Streptopelia, as many times these birds occupy different habitats. 

But a more clear situation of decline is shown by the sparrows, mainly by the Rock Sparrow (Petronia petronia), which is in the verge of the extinction in some of the islands (e.g. La Palma), while in others is becoming very rare and is highly localized in isolated areas. This is clear in Tenerife Island, where I live, as today the only area in which the species is common is Teno, in the west. Other small populations from the south of the island have dissapeared from the 90s and even in more recent years, as we have confirmed working in the field for the Breeding Bird Atlas of the Canary Islands (1997-2003), published in 2007 by SEO/BirdLife. 

Very interesting.  And puzzling.  In December 2012 the requests for information on bird control on the internet decreased over 90% for four commercial marketing firms after steadily increasing over the prior 10.  This is particularly evident and important in agriculture where the costs can be very expensive with lost crops and/or protection. This, along with my observations, lead me to believe that one of two possibilities existed; a change in climate or disease.  Or is it another factor that I've overlooked?  From your comments a clear cut pattern has yet to appear.  Or, is it too soon to speculate.

Thanks for your input.  Greatly appreciated.

In North African region (Algeria and Tunisia) there is a huge expansion of (Streptopelia decaocto) which replacing (Streptopelia senegalensis) at many zones. The first couple of  Streptopelia decaocto in Tunisia was recorded in 1994.

Changes in the avian diversity has been very noticeable in northeaster part of India. I have encloaed  one of my publication on this topic. 

I also live in the Pacific Northwest (dry side of the Cascades) and with the increase of Eurasian Collared-doves in my yard, I have seen a corresponding decline in native Mourning Doves.  This has been particularly noteworthy this fall.  I have counted the greatest number of Collared-doves using my feeders at one time (10) and with very few Mourning Doves (on average now only about 0-3 when I used to get up to 15).  During the breeding season, this wasn't so noticeable, but now that doves are flocking up, Mourning Doves don't seem to visit my yard nearly as much as Collared-dove numbers have increased.  Our autumn has been particularly mild, so Mourning Dove numbers should be high.  But, this doesn't seem to be the case.