Where are all the pigeons gone?

Where have all the pigeons gone? I commented on the springtime return of the ringed gulls today, to which a friend countered that he used to see a lot of pigeons, all year, scrounging in the gutter or otherwise mooching around, but doesn’t see them so much any more. When I thought about it, last week I noticed the flock of pigeons that loops over Jarry in Park Ex, but the general urban presence of the lone pigeon does seem to be diminishing.

We were wondering if this was some natural cycle or cause, or whether humans have intervened and done something to reduce pigeon fertility or something like that. Anyone know?