Silver gull

Abstract: Silver gulls can threaten the welfare of humans and other wildlife. Current superabundant gull numbers should be managed to reduce this risk. Denying gulls access to food at artificial sites, combined with direct population control, may reduce silver gull numbers in the long term. Control measures implemented at gull colonies overseas were trialled. Human disturbance in the colony associated with routine visits to study plots led to reduced nesting density. Egg-pricking reduced nesting success; it did not induce adults to incubate for extended periods even though gulls were recorded sitting on nonviable (although not pricked) eggs for up to 76 days. Removal of eggs from nests within experimental plots did not affect overall nesting success for these plots. Habitat modification, by mowing of long grass at the colony site prior to the commencement of breeding, decreased both the density of nests in mowed areas and nesting success. Selective culling of breeding adults from experimental plots was effective in reducing population size immediately and suppressed nesting by other individuals that attempted to breed later in the breeding season. The combination of habitat modification, culling and human disturbance reduced breeding success at colonies.

Abstract: -We examined colony and nest site selection in Laughing Gulls (Larus atricilla) from 1976 to 1979 in Barnegat Bay, New Jersey. Laughing Gulls nested predominantly in Spartina alterniflora on low salt marsh islands. In 1978, the gulls shifted colony locations to higher islands that contained a higher percentage of S. patens and Phragmites. The gulls nested on spoil areas which were slightly higher in elevation. Differential nesting success occurred as a function of habitat because of high tides in early July which wiped out all nests in S. alterniflora and most of those in S. patens. Chick survival varied as a function of vegetation type. We propose that all larid species exhibit site tenacity because they return to former sites even if they eventually shift locations. Further, we suggest that each species chooses from a wide range of potential colony and nest sites depending upon local conditions and proximate environmental cues. Many species of gulls and terns exhibit remarkable colony site tenacity in that they occupy the same places for decades or longer. This is particularly true of colonies situated in stable habitats such as rocky islands or cliffs: Black-legged Kittiwake (Rissa tridactyla) colonies use the same cliffs every year (Coulson and White 1956, 1958, 1960) and Glaucous Gulls (Larus hyperboreus) often nest on the same rocks in tundra lakes year after year (Snyder 1940). A colony of Black-headed Gulls (L. ridibundus) has remained at Ravenglass in England since the 1600's, nesting amid sand dunes and marram grass (Patterson 1965). Colony site tenacity has also been shown for the Herring Gull (L. argentatus; Tinbergen 1961, Ludwig 1963), Silver Gull (L. novaehollandiae; Murray and Carrick 1964), Glaucous-winged Gull (L. glaucescens; Vermeer 1963), Ring-billed Gull (L. delawarensis; Southern 1967), Black-headed Gull (L. ridibundus; Beer 1961), and Laughing Gull (L. atricilla; Stone 1937, Noble and Wurm 1943). Species that nest in unstable habitats, on the other hand, shift colony locations when habitats become unsuitable. Notable examples of such species are the Blackbilled Gull (L. bulleri, Beer 1966), Franklin's Gull (L. pipixcan, Burger 1974a) and Brown-hooded Gull (L. maculipennis, Burger 1974b). The first species nests on sand bars in the middle of rivers, and the latter two nest in marshes that suffer sporadic changes in water levels (Weller and Spatcher 1965). The apparent dichotomy between species nesting in stable habitats versus those in unstable habitats prompted McNicholl (1971, 1975) to postulate that colony tenacity relates to habitat stability. Colony site tenacity may not differ among species, but may relate to the conditions that particular members of each species face. A colony of kittiwakes might shift quickly if their cliff suddenly fell into the sea. Similarly, Laughing Gulls, usually considered to show a high degree of colony site tenacity (Bongiorno 1970, Nisbet 1971), may abandon colony sites when these become temporarily unsuitable. In this paper we report on colony and nest site selection in Laughing Gulls under normal tidal conditions (1976, 1977, 1979) and under unusually high tidal conditions (1978). At the beginning of the study, we did not know when flooding tides would occur, but planned to continue the study until we encountered these conditions. We wished to determine if Laughing Gulls would respond to exceptionally high tides by changing colony sites, changing nest ites, or both. Laughing Gulls nest from the Gulf of Mexico and the Caribbean to the northern Atlantic, although few colonies exist farther north than New Jersey. Along the middle Atlantic coast they nest in tidal salt marshes (Burger and Beer 1975), while south of the Carolinas they nest on sandy islands (Stone 1937, Buckley and Buckley 1972, Dinsmore and Schreiber 1974).

Abstract: The breeding biology of the Crested Tern Sterna bergii was studied on One Tree Island, Capricornia section of the Great Barrier Reef Marine Park, Australia. The dense nesting habit with its associated adaptations resemble those found in related species of terns. Clutch size was 1.01 with a mean incubation period of 28 days. Laying was spread over 53 days, but individual subcolonies were more synchronised (18 ± 11.5 days). Hatching success in 1979/80 was 69%, most failures being attributed to predation by the Silver Gull Larus novaehollandiae. Smaller subcolonies with proportionally more nests on the perimeter were subjected to greater predation of eggs than were large subcolonies. Overall, there was a decline in hatching success with season. Fledging success was high (85%) with most mortality in 1979/80 being the result of a tropical cyclone. Gulls stole from a third to half of the fish brought to the colony in January 1982. Fledging period varied between 35-43 days. The growth constant (K) was about 0.120, compared with 0.165 for the north temperate Sandwich Tern Sterna sandvicensis. These results are discussed with particular reference to Silver Gull predation.

Abstract: A total of 317 steps of walking Silver gulls (Larus novaehollandiiae) and filmed sequences of 24 other species of medium-sized and large birds were analyzed. The angles made by the tibiotarsus-tarsometatarsus joint of each leg during walking were measured. These varied depending on the species. In the Silver gull, where the angles were correlated with speed, the leg bent more sharply the slower the step; otherwise the angles were not correlated with speed. In all but the four largest birds, as in man, the leg was more bent in the middle of its stance phase than it was at the beginning or end of this phase. Thejoint was never completely straight, or 180″. In general the larger the bird, the slower was its step. The Silver gull and other birds do not bob their heads back-and-forth as they walk, but many birds do. It is not known why some birds bob their heads, although it may be correlated in part with a relative horizontal body posture, with seeing effectively, with balance during locomotion, or with habitat. The Silver gull does not hop, but some birds do, usually birds that live in the bush, or that are small.