Their distant ancestors raised their young at various times; those that raised them at the same time as the blue tits' ancestors had plenty of food and so their young were more likely to survive and raise chicks of their own, carrying the 'gene for' raising young at that time. Those that tried to raise their young at a different time were less successful.
That's what Darwin discovered 170 or so years ago (only he used different examples).
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They don't 'know' how to time it.
Their distant ancestors raised their young at various times; those that raised them at the same time as the blue tits' ancestors had plenty of food and so their young were more likely to survive and raise chicks of their own, carrying the 'gene for' raising young at that time. Those that tried to raise their young at a different time were less successful.
That's what Darwin discovered 170 or so years ago (only he used different examples).