APPEARANCE
For many years, the Yellow-legged Gull (Larus michahellis) was considered to be a yellow-legged subspecies of the Herring Gull (or what is now known as the European Herring Gull, Larus argentatus), but it was given species status by the British Ornithological Union in 2007. It is the same size as a Herring Gull, but the two species display geographical variations. Apart from being distinguished by its yellow legs, the Yellow-legged Gull has slightly darker grey coloration on the mantle and wings than in British Herring Gulls (Fig. 172), the white mirrors on the wing-tips of young adults are often reduced in size (as is also the case in four-year-old Herring Gulls), and in the breeding season the eye-ring is red rather than golden yellow.
FIG 172. Adult Yellow-legged Gull in summer plumage. (Alan Dean)
FIG 173. A Yellow-legged Gull is remarkably similar to a Herring Gull when the legs are not visible. (Alan Dean)
FIG 174. First-winter Yellow-legged Gull. (Alan Dean)
FIG 175. Adult Yellow-legged Gull with the inner primaries moulted and hardly any white tips on primaries 7–9. (Gzzz, Wikimedia Commons)
First-year birds are paler than Herring Gulls of the same age, except for the darker primaries. Their legs are not yellow as in the adults, but instead are pinkish grey, similar to those of Herring Gulls (Fig. 174). Adults nest at similar sites to those used by Lesser Black-backed Gulls (Larus fuscus), including buildings in Gibraltar, Spain, Italy and France.
SUBSPECIES
There are two subspecies of the Yellow-legged Gull. The typical form breeds throughout the Mediterranean and around the south-west coasts of mainland Europe, while the subspecies Larus michahellis atlantis breeds in the Azores, Canary Islands and Madeira. Some authors have suggested that atlantis individuals should be given species status. However, birds breeding in the Canaries and Madeira are intermediate in both plumage and size between those breeding in the Azores and on the mainland of Europe, so a specific status is probably not justified.
DISTRIBUTION
Numbers of Yellow-legged Gulls have increased in recent years and the birds have spread rapidly northwards in Europe, initially occurring in appreciable numbers in the non-breeding season and then, more recently, some arriving earlier and in time to breed. Most of the sightings in Britain initially occurred in southern England between July and October, and within the past 30 years their numbers have increased.
The increase in Britain is well illustrated by the analysis of records from the West Midlands made by Alan Dean for the period 1973–2000 (Dean, n.d.; Fig. 176). It is interesting that most records in the West Midlands occurred later in the year than those made in Sussex (Fig. 177), suggesting that perhaps birds on the south coast eventually move inland, joining up with the large numbers of other gulls that visit landfill sites between October and January. Numbers decreased in Sussex in winter, while many of the birds in the West Midlands stayed until February. These birds then departed south, leaving at the same time as most adult Herring Gulls at inland landfill sites left for their more northern breeding areas.
BREEDING
Offspring resulting from pairings of Yellow-legged Gulls with Herring Gulls and Lesser Black-backed Gulls have occurred in Belgium since 1996 and in the Netherlands since 1987. In 2002, the first pair of Yellow-legged Gulls was found breeding in Belgium, and breeding has recently spread further north to Denmark and inland to Germany and Poland.
The first attempted breeding in England occurred in 1992, when a single individual paired with a Lesser Black-backed Gull. The first breeding by a pair of Yellow-legged Gulls in Britain took place in Dorset in 1994 and continued at this same site in subsequent years. In 1999, one pair bred, and two mixed pairs were seen at three localities. Breeding attempts occurred in most years thereafter, but mainly as mixed-species pairs. In 2004, the first breeding attempt was recorded in Northern Ireland, in County Fermanagh, again by a mixed pair. By 2010, breeding attempts had been reported in at least six sites in the south of England, with the majority still forming mixed pairs either with Herring or Lesser Black-backed gulls and rearing hybrid offspring. In 2015, two pairs of Yellow-legged Gulls bred in south-west England and reared three young. Numbers of breeding records have increased slowly, although many birds are still forming mixed-species pairs.
FIG 176. The numbers of Yellow-legged Gulls reported each year in the West Midlands in England from 1973 to 2000. Numbers for 1973–1983 were annual averages over five-year periods. Based on data from Alan Dean (n.d.).
FIG 177. The summed monthly totals of records of Yellow-legged Gulls from 1973 to 2000 for Sussex and the West Midlands, England. The Sussex data have been extracted from the Sussex Bird Reports produced by Richard Fairbank and the West Midlands data are based on an analysis made by Alan Dean (n.d.).
Hybridisation has been frequently recorded between similar-sized gulls when one of the two species occurs in an area in small numbers, as when a species is extending its range. In the case of gulls, the hybrid offspring are viable, but whether they have reduced fertility is unknown. Hybrid young produced by Herring Gull and Yellow-legged Gull mixed pairings are difficult to identify as such in the field while immature, and this would probably also apply to back-crosses produced when the hybrids breed with Herring Gulls.
Following the range expansion and increase of the Yellow-legged Gull in many areas of Europe, it is likely to become a more frequent breeding bird in Britain and Ireland in the next few years, and there will be more same-species pairs breeding at more locations, as has happened in Belgium. In many aspects, this species is likely to compete with Herring and Lesser Black-backed gulls, and the outcome of this will be of considerable interest, although it is difficult to predict in advance. Since the Yellow-legged Gull already breeds in urban areas in southern Europe, it is likely to join the other large gulls breeding in towns and cities in Britain.