I'm a bit bemused by biscuitraider's attitude.
No one is raring to teach children about sex. I don't think I know anyone who can't wait for those conversations. But as the subject arises - as with the love making pigeons the op saw, then is the opportunity to give an age appropriate but honest answer.
Telling a child about sex doesn't make them rush out to have sex immediately. It gives them an idea of what is going on with natural body functions, and later on makes sure that they only do such a thing with full knowledge, and are less likely to be taken advantage of, or pushed into something they're not ready for. I'd strongly suggest that it is more likely to make sure that when they finally do such a thing, they are more likely to use protection, and be responsible about it.
This idea that sex ed makes kids have sex is something that ought to have died out generations ago. I remember it when I was at school - girls being pulled out of sex ed, as their parents felt they ought only to be told on their wedding night - if then!
Waiting until young people are sexually active is a bad idea - it's too late by then. You have to speak to them before they are sexually active.
And yes, they do get sex ed in junior school, around 7 or 8, I think my DD had it. But again, it's age appropriate - I went and viewed the videos myself. It's basic facts, and includes info on relationships & pressure, etc. Sex ed continues up through school - each time at a correct level for this age.
So at what age do you think information should be given, and what level of information?