To find the expected number of birds with lengths between 15.4 cm and 16.8 cm, we first standardize the lengths using the formula for the standard normal distribution:

\(Z = \frac{X - \mu}{\sigma}\)

For 15.4 cm: \(Z = \frac{15.4 - 16.5}{0.6} = -1.833\)

For 16.8 cm: \(Z = \frac{16.8 - 16.5}{0.6} = 0.5\)

We need to find \(P(-1.833 < Z < 0.5)\).

Using the standard normal distribution table, we find:

\(\Phi(0.5) = 0.6915\)

\(\Phi(-1.833) = 1 - \Phi(1.833) = 1 - 0.9666 = 0.0334\)

Thus, \(P(-1.833 < Z < 0.5) = 0.6915 - 0.0334 = 0.6581\).

The expected number of birds is:

\(0.6581 \times 150 = 98.715\)

Rounding to the nearest whole number, we expect 99 birds.