nominate Lesser Black-backed Gull (L. f. fuscus)

(last update: 20-11-2014 )

Northern Norway: breeding ground for dark-mantled and pale-mantled LBBG

Traditionally, two subspecies of LBBG could be found in Norway: dark-mantled nominate fuscus in the north and pale-mantled intermedius in the south. Last decades, nominate fuscus breeding figures have dropped dramatically, while those figures for pale-mantled birds have increased. Nowadays (but already from the late 1980's) pale-mantled birds, either with origins in graellsii-land or colonisers from south Norwegian intermedius-land can be found way up in northern Norway.

The likelihood of mixed pairing becomes larger. It is interesting to see how these populations evolve, both in phenotypics and in migration strategy. There has been a publication on interbreeding (foster parents in fuscus x argentatus). The summary is copied below.

ABNORMAL MIGRATION AND HYBRIDIZATION OF LARUS ARGENTATUS AND L. FUSCUS AFTER INTERSPECIES FOSTERING EXPERIMENTS

M. P. Harris, 1970 IN: Ibis, Volume 112, Issue 4, pages 488–498, October 1970

Summary

Between 1962 and 1966 eggs of Larus argentatus and L. fuscus were interchanged and almost 900 young were reared by the wrong species. Many of these cross-fostered young were later recovered or retrapped on and away from the colonies.

The British population of argentatus is sedentary and ringed birds are not recovered outside Britain, whereas fuscus normally migrates. Many cross-fostered argentatus migrated to France, Spain and Portugal, areas where fuscus is common, but they did not migrate as far as the control fuscus. It is possible that these cross-fostered argentatus had followed their foster parents when these migrated, but this is unlikely as the cross-fostered fuscus also migrated although their foster parents would have remained in Britain.

Despite wide ecological and behavioural overlaps, interbreeding between L. argentatus and L. fuscus is exceedingly rare. However, as a result of cross-fostering experiments, 31 and 40 mixed pairs were found on Skokholm in 1968 and 1969 respectively. Although some of the birds involved were unringed it is probable that all the adults in mixed pairs had been cross-fostered. Other cross-fostered birds were found mated with their own species and it appears that the sex of the imprinted birds was important. Female gulls will usually only mate with males of their own species, or in the case of the cross-fostered birds, with males of their foster species. Males will mate with either species.

Evidence is given that suggests that the colour of the mantle and wings is important in species recognition at long range, and the colour of eye-ring and join of the mandibles for recognition at short range. The role of voice is uncertain but general behaviour is probably unimportant.