[chris (OP)]

Sitting in my garden over the weekend I spotted a pair of blue tits setting up home in a nest box on the fence. This prompted us to start wondering whether they find a mate, then make babies, then build a nest while the eggs develop, then lay the eggs, or some other order.

Does anyone know?

[Colin2B]

Depends on the bird species. Quite a lot go through courtship displays, mate and then build a nest, but some, mainly the male, build a nest which attracts the female who appears to choose the best nest - perhaps based on location.
Others, like Ospreys use the same nest each year and often mate on it.

[chris (OP)]

So how long after they mate are the eggs ready to be laid?

[Colin2B]

So how long after they mate are the eggs ready to be laid?

Sorry, missed this.
Fertilization doesn't necessarily take place immediately after mating, domestic chickens and turkeys can produce fertile eggs seventy days after copulation. Some wild birds are known to be able to store sperm for 16 days, probably so they can choose the best time to lay.

Normal delay between mating and laying varies by bird eg Finches usually lay 5-7 days after mating, Eagle within 5-10 days, Cockatoo usually lay within 7-10 days of mating.

[chris (OP)]

The birds court and then pair, presumably? So what's the sequence of events? Do they seal the deal and mate in a tree and then look for a house, or do they pair up, do the house-hunting and then "christen" their new abode?