Your bird photos look good, with the nice backgrounds. If these are JPEGs perhaps you could adjust the settings in your camera. Or you could change these a little with software. Even though our older cameras often still take good pictures, you might consider upgrading your camera. More megapixels give us extra to crop. That helps with the relatively short range of the 55-250mm lens. If you are patient, I think the rumored Canon T5i (700D) or Canon 70D are going to be a significant upgrade. Wait for them to be released and reviewed. Assuming it all turns out good, that could be something to start saving for now.