Because modern blue tits simply don't want to have that many offspring anymore Because a nest with twelve eggs is overcrowded and bound to have low success Because they don't know any better (birds...

Extracted text: Because modern blue tits simply don't want to have that many offspring anymore Because a nest with twelve eggs is overcrowded and bound to have low success Because they don't know any better (birds are not called feather brains for nothing) Because taking care of 12 rather than 9 eggs and nestlings means that the parents have to divide up their energy more and the survival of the individual nestling will be lower Because producing 12 eggs costs much energy, which then isn't available for parental survival and investment in future reproduction O Because there are already too many birds


Extracted text: Consider the following graph showing clutch sizes and fledgling rates of blue tits. 1000 1.0 800 0.8 600 0.6 400 0.4 200 0.2 ㅇ 0.0 1 3 5 7 9 11 13 15 17 Clutch size The line shows the average number of fledglings surviving (on right y-axis) for a given clutch size (on the x-axis). The histogram bars show the frequency of nests observed (on the y-axis) per clutch size (on the x-axis). Why do most pairs lay fewer eggs (9), than the clutch size with the highest return of fledglings (12)? Frequency Young/clutch