Dave Hazard
The expanding population of the Lesser Black-backed Gull Larus fuscus in Britain stood at 83,500 breeding pairs in 1991 (Gibbons et al. 1993), with inland colonies doing particularly well when left alone from culling and disturbance. According to Gibbons et al. (1993) colonies in Yorkshire are few and far between. The only substantial one for 100km or more of Doncaster appears to be in north Nottinghamshire. Large colonies comprising several thousands of pairs exist at coastal sites, South Walney in Cumbria being a typical example, and one from which Doncaster has a 1995 ringing recovery (at Southfield Reservoirs). Our own DDOS records show a healthy and increasing winter population, especially at roosts, and also good numbers of summering birds (predominantly non-breeding immatures).
Dale Pit Quarry is a presently unworked sand and gravel quarry, inundated with water, and situated near Hatfield Moors. The old workings provide valuable breeding habitats for a host of species, including a growing colony of Black-headed Gulls L. ridibundus, which has increased from 100 pairs to nearly 200 pairs over the past two years. On each visit to the site through the summer, substantial numbers of Lesser Black-backs were also noted. Most appeared simply to enjoy the security and company of other gulls loafing and preening on the colony edge. Numbers varied, but regularly reached 50 birds, the main components of which were first-, second- and third-year immatures. These were obvious non-breeders, with varying amounts of brown plumage clearly evident. However, a small number of adult Lesser Black-backs were also present, raising the question as to why these birds in early to mid-June were not breeding. The simple answer is that they were.
On two visits in early June, two adult Lesser Black-backed Gulls followed one observer closely around the site, whilst the other Lesser Black-backs, some 40-50 birds of varying ages, flew from the small islands and water where they had been preening, to a banked area at the edge of the site. The two adults stayed overhead at heights ranging between 3-10m and were heard to utter a soft guttural ‘grrrrh” call. Unlike the attendant Black-headed Gulls that occasionally harried the observer, the two adult Lesser Black-backs simply remained close by the observer. They moved back to rest on the islands as the Black-headed Gull colony settled when the observer appeared to be at a safe distance. The observer felt that the behaviour of these two adults was a form of territorial defence (N.P. Whitehouse pers comm.).
Whilst visiting the islands on 14th June to ring Black-headed Gull chicks, an oversized nest containing three large, distinctive gull-type eggs was located on one of the peripheral islands close to the water’s edge. The only other nest on this relatively small island (2m x 1m) was that of a Common Coot Fulica atra, containing six eggs. Subsequent observations from a distance identified the nest’s owner as Lesser Black-backed Gull, which had to withstand heavy mobbing from the Black-headed Gulls when moving to and from its nest. The presumed male (non-incubating bird) swam around close to the island and displayed a distinctive darker grey mantle and wing-coverts than the female. Unfortunately, a week later the nest was empty, and the eggs assumed to have been predated, although oddly, the Common Coot’s nest prevailed and the eggs were just hatching.
However, during a later ringing visit on 21st June, two gull chicks were picked up adjacent to a single large nest, again on a peripheral island, this time more centrally located, and obviously not a Black-headed’s. Instead of the expected sandy brown down with dark chocolate markings, these youngsters were pale grey with darker grey and blackish markings. Although clearly very young, these two birds were as large as three-week-old Black-headed Gull chicks. Again, observation from a distance confirmed the parents of these downy grey chicks to be Lesser Black-backs, and thus a second breeding pair. A return visit several days later found only one chick still surviving, which became the first pullus ringed in the Doncaster district. Whether or not the youngster managed to fledge remains unknown as no further visits were made.
Reference
Gibbons, D.W., J.B. Reid and R.A. Chapman (compilers) (1993) The New Atlas of Breeding Birds in Britain and Ireland: 1988-1991. London.