Birthday boys

[Tintin]

The 'On this day' section on the main page will have its two longest birthday lists today and tomorrow. Four Bangladesh cricketers have their date of birth as December 31 and seven have January 1. This is against only three DoBs in whole of May and four each in April and August.

Why do so many people have their January 1 as their date of birth ? Is there any practice (while enrolling children in schools, for eg) of using it as the default DoB if the exact date is not known ?