A new report says the number of boys born in the United States and Japan has decreased every year since 1970.

　　The report says the reason for the decrease is unclear.

　　But it says environmental and other influences might be involved.

　　American and Japanese researchers studied 30 years of birth records from the two nations.

　　The researchers say they found fewer boys were born in comparison to girls.

　　They say the decrease is births was equal to 135,000 white males in the United States.

　　In Japan, the decrease was equal to 127,000 fewer males.