Gaviiformes is a bird order that comprises the loons. Apart from numerous extinct species, five species are placed in the genus Gavia:
- Red-throated Loon (G. stellata)
- Black-throated or Arctic Loon (G. arctica)
- Pacific Loon (G. pacifica)
- Common Loon (G. immer)
- Yellow-billed Loon (G. adamsii)
Hybrids within this group of birds are not common, but a few have been reported and described. McCarthy (2006) lists the following natural hybrids:
- Yellow-billed Loon x Common Loon
- Arctic Loon x Common Loon
- Common Loon x Pacific Loon
- Common Loon x Red-throated Loon
One study describes a hybrid between Yellow-billed Loon and Common Loon based on a museum specimen from the collections of the Zoological Museum Amsterdam (Roselaar et al. 2006).
Roselaar, C. S., Prins, T. G., Aliabadian, M. & Nijman, V. (2006). Hybrids in divers (Gaviiformes). Journal of Ornithology 147, 24-30.