Although molecular biologists may have useful information for ornithologists, they usually overlook the possibility that ornithologists might also be able to tell them something. From work in the field and with museum specimens, I know most of the smaller, more or less masked, southern gulls whose affinities Given et al. (2005) analyzed, and I have some problems with their conclusion that these species are all related to each other and also to the northern Black-headed Gull (Larus ridibundus).

First, Given et al. are not the first to suggest that the Black-headed Gull has a southern relative. Murphy (1936:1084) wrote of the Brown-hooded Gull (L. maculipennis):

While I agree, I believe that the other small southern gulls, Hartlaub's Gull (L. hartlaubii) of South Africa, Silver Gull (L. novaehollandiae) of Australia, and Red-billed Gull (L. n. scopulinus) and Black-billed Gull (L. bulleri) of New Zealand, though all similar as reported by Johnstone (1982), are rather different from the Brown-hooded Gull, and closer to the Brown-headed Gull (L. brunnicephalus), which breeds on the “roof” of Asia and winters around its southern and eastern coasts (Bourne and Bundy 1990).

The most distinctive feature of these gulls is not the hood of the breeding season, which seems to come and go according to what allies breed nearby, but the wing pattern, which is visible at a distance in feeding flocks throughout the year. The Brown-hooded and Black-headed gulls, as well as the northern Slender-billed Gull (L. genei) and Bonaparte's Gull (L. philadelphia), have a white bar at the front of the adult wing. The others, like the gray-headed gulls (L. cirrocephalus and L. c. poiocephalus) of tropical South America and Africa, have dark wingtips with white marks. The late James Fisher (pers. comm.) suggested to me that the masked gulls must have evolved around the fluctuating water masses of the central Old World in the late Tertiary or Pleistocene. It seems incredible that a southern gull could have reached the Tibetan plateau, so surely the first step in their dispersal was the colonization of the Southern Hemisphere by early brownheaded-type gulls wintering to the south, which gave rise progressively to the tropical gray-headed gulls and the temperate, white-headed Silver Gull and its allies?

We now come to the really interesting question. These allies may have included the Brown-hooded Gull, which is masked and pinkish in the spring. As Given et al. (2005) suggest, this species may then have recolonized the Northern Hemisphere, giving rise not only to the Black-headed and Bonaparte's gulls, which retain a mask but do not turn so pink, but also their nearest ally, the Slender-billed Gull, which has lost its mask but turns pink in the spring. Alternatively, the Brown-hooded Gull may be an independent derivative of the Black-headed Gull in the Southern Hemisphere, the latter having reached South America with the aid of the northeast trade winds. A banded bird from the east Baltic Sea has reached Barbados (Cramp and Simmons 1983).

Considering the molecular evidence provided by Given et al. (2005), it is unfortunate that, like some other authors (Bourne 2002), they seem to have ignored critical forms, especially the well-differentiated central Asian masked gulls that may be derived from the original stock, including not only the Brown-headed Gull but its possible allies, Relict Gull (L. relictus), Mediterranean Gull (L. melanocephalus), Great Black-headed Gull (L. ichthyaetus), and Saunders's Gull (L. saundersi). In fact, although they may have included the Prince of Denmark in their version of Hamlet, they seem to have left out his father (reputedly played by Shakespeare himself).

Data in table 2 of Given et al. (2005) imply that Slender-billed and Bonaparte's gulls are early derivatives of the primitive stock left behind in the Northern Hemisphere when it colonized the south; Black-headed and Brown-hooded gulls then showed convergent evolution in the opposite hemisphere after the Black-head Gull moved back north. An alternative interpretation is that the molecular differences are attributable to the degree of isolation of members of a group of birds prone to wide dispersal and frequent hybridization, which has left the forms that are found closer together, notably in Australasia, molecularly more similar than those found farther apart. If so, did the Brown-hooded Gull move back north and give rise to the Black-headed, Slender-billed, and Bonaparte's gulls, or did one of them or a common ancestor move south independently and give rise to the Brown-hooded Gull? More evidence is required to elucidate this.