Initializing array of std::vector in constructor init list

Usually when writing a constructor I try to initialize as many class members as possible in the member initialization list, including containers such as std::vector.

class MyClass
{
  protected:
  std::vector<int> myvector;

  public:
  MyClass() : myvector(500, -1) {}
}

For technical reasons, I now need to split this into an array of vectors.

class MyClass
{
  protected:
  std::vector<int> myvector[3];

  public:
  MyClass() : myvector[0](500, -1), myvector[1](250, -1), myvector[2](250, -1) {}
}

Turns out, I cannot initialize the array of vectors this way. What am I doing wrong? Or is this just not possible?

Of course I can still do this in the body of the ctor using assign, but I'd prefer to do it in the member init list.