The Internet has recent sported people stating that feeding mealworms may be a problem for wild birds.  It is not!

The following article talks about the relationship of calcium and phosphorus whereby phosphorus will bind with calcium and can cause a deficiency of calcium absorption in birds.

The article points out that the real issue is with captive birds; not wild birds.  Wild birds will balance their diet and most feeding stations offer a variety of food besides mealworms.

Calcium, Phosphorus and Vitamin D3 Imbalances by Peter Sakas  DVM, MS.