The rapid moult strategy of nominate fuscus makes it difficult to distinguish all sub-adult birds from adults. In some individuals it may be difficult to distinguish 3cy birds from 4cy. Lars Jonsson's article in Birding World shows the plumage characteristics in detail. In 3cy spring birds, fuscus normally shows a pale yellow bill, already a red gonydeal angle and the iris is pale yellow. Primary moult may start again in 3cy birds in March and result in a clear division of old third generation and new fourth generation inner primaries when fuscus returns at northern latitudes in summer. Most often, a clue of immaturity can be found in the tail; a few tail feathers have been moulted and are clear white, some older feathers show black spaghetti or vermiculated pattern. In 4cy birds, except from some odd black markings in the tail, these sub-adults are hard to tell from adults.

Organochlorine concentrations in diseased vs. healthy gull chicks from the northern Baltic.

by: Martti Hario, Juha-Pekka Hirvi, Tuula Hollmen, Eeva Rudback

IN: Environmental Pollution 127 (2004) 411–423.

Abstract

The population decline of the nominate lesser black-backed gull Larus fuscus fuscus in the Gulf of Finland (northern Baltic) is caused by an exceedingly high chick mortality due to diseases. The chick diseases include degeneration in various internal organs (primarily liver), inflammations (mainly intestinal), and sepsis, the final cause of death. The hypothesis of starvation causing intestinal inflammations (leading to sepsis) was tested by attempting to reproduce lesions in apparently healthy herring gull L. argentatus chicks in captivity. The herring gull chicks were provided a similar low food-intake frequency as observed for the diseased chicks in the wild. However, empty alimentary tract per se did not induce the intestinal inflammations and therefore, inflammations seem to be innate or caused by other environmental factors in the diseased lesser black-backed chicks. They had very high concentrations of PCB in their liver; but the concentrations were not significantly higher than those of the healthy herring gull chicks, indicating a common exposure area for both species (i.e. the Baltic Sea). When compared to NOEL and LOEL values for TEQs in bird eggs our TEQ levels clearly exceed most or all of the values associated with effects. Compared with published data on fish-eating waterbirds, the DDE concentrations in the diseased lesser black-backed chicks were well above the levels previously correlated with decreased reproduction, while the residues in apparently healthy herring gulls were below those levels. The DDE/PCB ratio in lesser black-backs was significantly elevated, indicating an increased exposure to DDTs as compared with most other Baltic and circumpolar seabirds. The possible exposure areas of DDT in relation to differential migration habits of the two gull species are discussed. FULL PDF