So these are our hamsters. They were about the same size when we first bought them but now the pale one has grown really big and chubby while the darker one is small and kind of scrawny. Big one is very active and busy, little one spends most of her time in her nest, she's a little bad tempered when getting her out of it but friendly as can be when you get her out and about. I guess I'm just a bit worried that littler hamster might not be thriving. Any advice?