Enjoying the sunshine

This is Marshall's new favorite spot now that spring has come and we've opened the windows. He can sit for hours looking out the window (and he is a very active cat!) The only problem, though, is that he's getting too big to fit on the windowsill unless the window is open. Notice the size differential between the cats. Marshall no longer looks like a kitten and I think Miles will look like a kitten for the rest of his life! He's had lots of recurring health issues and he's still a teeny little kitty, weighing in at just over 3 pounds. If anybody has any good ideas on how to beef up one cat while slimming down the other, please do share!