Chinese Chicken

There was a father who was very close to his son. They used to go everywhere together including calling "chicken" (Chinese slang for prostitute).

One day, the son decided to go oversea for study. The father was very supportive.
Before his son left, the father told the son, "We cannot look for chicken together for the next few years. However,if you need to call chicken, please go ahead and I will pay for it. But please state the expense as 'Shooting Bird' so that your mum will not suspect."

So the son left. For the first month, the father received the bill from the son (shooting bird - $1000).
Subsequently for the next few month, the bill for shooting bird is above $1000. The father could not tolerate this any more, so he wrote to his son.
"Son, you have been shooting too expensive bird, try some cheaper one".

A month later, the father received another bill from his son. It wrote: "Shooting Bird - $50 Rifle Repair - $2,000"