The mantle is the back of the gull. In this chart, colors are shown on
a scale of 1 to 8.5, with 1 the lightest and 8.5 the darkest, a charcoal.
| Species | Age group | Mantle color |
| Glaucous | Adult | 1.0000 |
| Herring | Adult | 2.0000 |
| Ring-billed | Adult | 2.0000 |
| Bonaparte's | Adult | 3.0000 |
| Thayer's | Adult | 3.0000 |
| Glaucous-winged | Adult | 5.0000 |
| California | Adult | 6.0000 |
| Glaucous-winged-Western Hybrid | Adult | 6.0000 |
| Mew | Adult | 6.0000 |
| Black-legged Kittiwake | Adult | 6.5000 |
| Heermann's | Adult | 8.0000 |
| Western | Adult | 8.0000 |
| Slaty-backed | Adult | 8.5000 |