Depends on the extrapolating function.

It could (reasonably) be anywhere from 2 to 64.

2: static value of N birds in hand. F(N)=2

16: each bird in hand is worth 2 in bush: F(N)=2×N

64: Each Bird in the hand is some Linear combination of birds in bushes:

F(N)=A×N^2 + B×N + C

For F(1) = A + B + C = 2

For F(8)= 64A + 8B + C = 64

62 = 63 A + 7B

Etc.

In any case, we'd need more hand bird to bush bird data points to make any fair assumption.