102,030 research outputs found
An ecological approach to the management of gulls, in particular the lesser black-backed gull Larus Fuscus (L. 1758)
No full textA study of gull management was made at a large colony of Lesser Black-backed Gulls Ljxrus fuscus on Tambrook Fell, Lancashire. Approximately 18,000 gulls presently breed at the site, and the area utilised by the gulls extends over 6 km2 on three private estates. The main studies were conducted on the Abbeystead Estate between 1992 and 1994. The reasons for increases in the numbers of several gull species in many parts of the world during the 20th century are presented, as well as the conflicts with humans caused by these increases. The practical and moral aspects of managing gulls are evaluated, as well as the conflicts likely to result from recent increases in the urbanisation of several Larid species. The need for management strategies to incorporate up-to-date knowledge of gull demography, density dependence, breeding biology and behaviour are discussed in the light of the limited success of past attempts at managing gulls. Experiments to entirely clear specific areas of the Tambrook Fell Gullery by disturbing breeding gulls are described. The aim was to ameliorate local problems by reducing the extent of the colony using non-lethal management techniques. Disturbance was carried out in a series of 2.25ha experimental plots. Audio, visual and physical disturbance methods, presented singly or in combination, were used to investigate their ability to exclude gulls and prevent breeding. The number of gulls using the plots and the number of nests built were compared with numbers on control plots. Gulls showed habituation to all disturbance methods, although the number of gulls using a plot was reduced during disturbance and a proportion of the original number of gulls were totally excluded. Only where two disturbance methods were utilised on the same plot was breeding completely prevented. It was demonstrated that disturbance was more effective when initiated prior to the start of nest building and when conducted at the edge of the colony, and that disturbance by human presence is an effective method of preventing breeding. In the year following disturbance, only a very few gulls attempted to utilise the disturbed areas, and the need to establish a 'sink' area for birds displaced by disturbance is discussed. In two seasons, a total of 75ha were cleared of breeding gulls. This was 23% of the Abbeystead Estate and 11 % of the total gullery area. This was the first time in over thirty years of management efforts at the colony, that the extent of the gullery was successfully reduced. Models are presented to show the effects of the 1978- 1988 culls on adult survivorship and recruitment into the breeding group at Tambrook Fell. The relative effects of management strategies aimed at survivorship and productivity are discussed. A study was made to quantify the percentage of nests built by gulls at the colony that are not subsequently laid in. Behavioural differences between pairs that failed to lay eggs and pairs that successfully bred are presented. In the past, calculations of the number of breeding gulls at the colony assumed that one nest represented one pair. This was shown not to be true and a correction factor (multiplier) of 0.61 was calculated to allow counts of nests at the colony to be converted to the number of breeding pairs
Distribution, diet and kleptoparasitic behaviour of gulls (Aves: Laridae) in the southwestern Cape Province, South Africa
No full textBibliography: leaves 159-175.The southwestern Cape coastline supports only two common, resident gull species, Hartlaub's Gull Larus hartlaubii and the larger Kelp Gull L. dominicanus. Hartlaub's Gull is endemic to southern Africa and the Kelp Gull that occurs in this region is sub-specifically distinct, L. d. vetula. Although locally abundant, both the Kelp and particularly Hartlaub's Gull have been relatively little studied. This study addressed three aspects of the two gull species' ecology related to foraging. The diet of both species was studied through direct observation and analysis of pellets, scats and stomach samples. Diet was quantified at a range of foraging habitats; (i) a sandy beach; (ii). a rocky shore; (iii) a fishing harbour; and, (iv) a refuse dump. In addition, the proportion of marine prey in the diet of Kelp Gulls at a refuse dump, a sandy beach and at archaeological sites was estimated using stable carbon isotope analysis of bone collagen. Both gulls are generalist foragers feeding on a wide and diverse range of prey species. The Kelp Gull is able to feed on a wider range of prey species than is Hartlaub's Gull due to its larger size. The preferred natural foraging habitat of the Kelp Gull is sandy beaches, where the sand mussel Donax serra is the most important prey. Present day Kelp Gull diet at an undisturbed• sandy beach includes a similar proportion of marine protein to prehistoric gull diet in the same area. Hartlaub's Gull most commonly forages on swarms of invertebrates associated with accumulations of stranded kelp e.g. Ecklonia maxima
Sex allocation and reproductive costs in a gull with a long breeding season
No full textThe Silver Gull is a small gull (265 - 450g), which exhibits sexual dimorphism, with males larger than females. It has a protracted laying period of about 8 months over the winter on Penguin Island in Western Australia. The Silver Gull was studied on Penguin Island from 2000 to 2002. Completed clutches were removed from breeding pairs to induce repeat laying in order to determine the effect of increased reproductive effort on maternal body condition, egg production ability, offspring sex ratio and chick rearing capacity.
Increased egg production had no significant effect on maternal body condition as measured by condition index, derived from mass divided by a measure of skeletal size. The seasonal period, divided into thirty-day intervals, had a significant impact on female condition index, with a decline in condition toward the end of the breeding season. While male condition also appeared to decline at the end of the season, this pattern was not significant.
The initiation of laying varied between the three years of the study. The earliest occurred in 2000, which also experienced earlier rainfall than the later two years. Egg size and mass decreased throughout the breeding season although the number of eggs in a clutch did not decline. The size and mass of the eggs was significantly affected by the laying history of the parents, although this effect was dependent on the year in which the eggs were produced.
The minimum interval required by Silver Gulls to replace a lost clutch is about 14 days. This interval increased from the start of the breeding season, but then declined toward the end, as summer was approaching. Laying interval increased significantly as the number of clutches produced by the parents also increased, up to 4 clutches in total. As more clutches were produced past this point, the laying interval became shorter.
The probability of a replacement clutch being produced after clutch removal, declined as the clutch number increased and as the season progressed. Individuals that laid clutches with a larger mean mass were more likely to lay a replacement clutch. Increasing reproductive output caused a decline in the proportion of clutches that were replaced after clutch removal. The proportion of clutches that were replaced also varied between the years with the highest rates of replacement seen in 2000 which was also the year that experienced the earliest start in laying. The size of the original clutch in terms of its mean mass and volume was related to the size of the replacement clutch, but this relationship varied according to the timing of laying.
During 2000 and 2001 male offspring predominated in the first two clutches produced by Silver Gulls. Further clutches that were produced demonstrated a sex ratio skewed toward females, the smaller sex in this species. Offspring sex ratio was close to equality in 2002 with very little effect caused by increased egg production. There was no effect of year, season or the laying history of the parents on hatching success. Growth rate in chicks was influenced by the year in which the chick hatched, the period during the season in which the chicks hatched, its sex and the laying history of the parents. The relationship between chick growth and the laying history, however, was complex with no consistent pattern emerging in terms of the performance of chicks from each treatment group. While the chicks from control groups generally grew faster than the chicks from manipulated parents, those individuals that were laid or raised by manipulated parents that had laid at least three clutches in total also performed well.
Using the two main measures of reproductive success in the current study, egg production and chick rearing, those birds that were induced to lay multiple replacement clutches, were able to maintain a high level of condition and reproductive success. It is proposed that in the Silver Gull, only those individuals with a high level of condition continue to lay replacement clutches. If the female is unable to produce well provisioned eggs with a high chance of success, the breeding attempt is abandoned. Despite no loss of condition detected in female Silver Gulls with increasing clutch number, there was a significant shift in the offspring sex ratio toward females, indicating that strategies were in place to cope with the increased reproductive effort incurred as a consequence of repeat laying. Protracted laying in this species allows replacement of lost clutches only after maternal condition has been regained after laying
Heavy metal pollution and blackheaded gull (larus ridibundus L.) breeding ecology
No full textHeavy metals in air, soil and water are a global problem and present a growing threat to the environment. These metals may have profound consequences for birds and can cause a number of sub-lethal effects, such as decreased reproductive success. The concentrations of selected heavy metals (As, Cd. Co, Cu, Fe, Pb, Mn, Ni, V, Zn) and Se in eggs and feathers from populations of black-headed gulls (Larus ridibundus L.) located on different colonies in the UK, which have different characteristics and are subject to different sources, types and degrees of pollution, were examined. Concentrations of As, Cu, Pb, Ni, Se and V measured in black-headed gull eggs were consistently high relative to those reported in previous field studies with other gull species. However, no significant effect was observed on the egg characteristics in terms of egg size and dimensions, shell thickness and index as a result of concentrations of metals measured in this study. Concentrations of Co, Fe and Ni were significantly negatively correlated with yolk:albumen ratio in the egg. The usefulness of sampling eggs to provide a reflection of local contamination has been demonstrated, with concentrations related to local sources of metal pollution and site differences reflected in sediment concentrations from previous studies. The importance of taking into account diffuse and historical pollution in addition to point source discharges has also been highlighted. As, Fe, Mn, Pb, Se, V and Zn were found at significantly higher concentrations in egg contents than egg shell, and Cd, Co and Ni concentrations were higher in shell than contents. Cu was distributed approximately equally. Within the egg contents, concentrations of As, Cu, Se and V were higher in the albumen than in the yolk, and Co, Fe, Mn, Ni, Pb and Zn concentrations were higher in the yolk than the albumen. Cd was found mainly in the shell and concentrations in egg contents were largely undetectable. Comparisons were made between a colony subject to high-level commercial egg harvesting and an un-harvested site, and between pre- and post-harvesting eggs on the harvested site. Postcollection eggs were found to be of significantly lower quality than the pre-collection eggs and the eggs from the uncollected site, as indicated by yolk:albumen ratio. Concentration of metals in eggs as a result of relaying forced by commercial harvesting has been demonstrated, with concentrations of Co, Fe and Ni significantly higher in post-collection eggs compared to precollection eggs. Average nesting density was significantly lower on the collected colony than the uncollected colony. No effect on egg size was found as a result of changes in nesting density. Concentrations of metals in black-headed gull chick down were measured and compared to egg data in order to assess the usefulness of feathers as a tool for non-destructive monitoring of metal pollution. The results suggest that feathers may be good indicators for As and Zn, and possibly also for Mn and Ni. However, the sample masses were very small and for a number of metals concentrations were largely undetectable using the analytical equipment available in this study. Future work with larger samples of down would be prudent to further examine the use of chick down to provide an indication of the level of pollution to which birds are exposed. The importance of using appropriate washing procedures to remove exogenous contamination of feathers to assess internal concentrations has been demonstrate
Aspects of the ecology of the black-headed gull (larus ridibundus) with comparative data on the common gull (L. canus)
No full textBetween 1982 and 1984, 893 Black-headed and 117 Common Gulls were trapped outside the breeding season in northeast England, and individually marked with wingtags or colour-rings. About 40% of marked adult Black-headed and Common Gulls returned to the study area in subsequent years, although adult Black-headed Gulls marked at the coast in the 1982-83 season returned in considerably higher proportions. Proportionately fewer second-year and first-year birds returned than adults. These percentages are considerably lower than the estimated annual survival rate for Black-headed Gulls, showing that some of the birds probably spent subsequent winters outside the study area. Some of the birds which did not return to the study area were recovered or seen elsewhere, mainly in eastern parts of Britain: few moved to the west coast. Foreign Black-headed Gulls which overwintered in the British Isles were most numerous compared to British birds in the south and east of the British Isles. A small proportion of Continental Black-headed Gulls remained in Britain during the breeding season: the consequences of these birds joining the British breeding population are discussed. Overwintering Black-headed Gulls in the study area were observed feeding inland on fields and refuse tips, and at the coast. First-years were uncommon compared to adults at the coast, less so on tips, and were relatively most common on fields. Females made up similar proportions of flocks at the coast and on inland fields, but were excluded to some extent from tips. Neither the survival rates of adult and ■ first-year British Black-headed Gulls, nor the weights of adult Black-headed Gulls caught in northeast England, were usually affected by the severity of weather in winter. The migrations and movements of Black-headed Gulls are discussed and compared to those of other species
Divorce in the kittiwake gull rissa tridactyla
No full textDivorce has been observed in many species of bird. Studies have revealed a relationship between divorce and reproductive success. This study was carried out to investigate whether such a relationship exists in the Kittiwake (Rissa tridactyla). The aims were to determine when divorce occurs, what causes divorce to occur, what the effects of divorce on reproductive output are and, finally, why birds divorce. It was conducted at a warehouse on the north bank of the River Tyne in North Shields, Tyne & Wear, during the 1990 breeding season. Analysis of a long-term data set spanning thirty three years was also carried out. Divorce does cause a significant reduction in some measures of reproductive output, acting significantly during incubation. Divorce may be due to lower reproductive success in the preceding season, a possible result of incompatibility between individuals
Aspects of the ecology of gulls in the urban environment
No full textA survey in 1994 recorded nearly 14,000 pairs of Larus gulls of four species nesting on buildings in Britain and Ireland. The majority of these records involved Herring Gulls, although large numbers of Lesser Black-backed Gulls were also observed. Since the last such survey in 1976, Lesser Black-backed Gulls had shown the highest rate of increase. Despite the sharp decline in the numbers of Herring Gulls breeding in Britain and Ireland since the mid-1970s, numbers nesting on roofs had continued increasing, albeit at a lower rate than before. New developments since 1976 included increasing numbers nesting inland and on the roofs of large industrial buildings. The study of a colony of Herring Gulls and Lesser Black-backed Gulls nesting on one such industrial building showed that the breeding success of these birds, although lower than that found for roof-nesting birds at more dispersed colonies, was higher than that at many traditional colonies. Low nest density, shelter for chicks and safety from predators were thought to be important contributors to this success. In addition, die colony was situated very close to the sources of food, agricultural land and urban areas, found to be most important in die diet of Herring Gulls nesting there. A review of dietary studies of roof-nesting Herring Gulls found that, despite the location of such colonies in urban areas, urban sites were not always an important source of food. The reduction in availability of one urban source of food, untreated sewage, was found to have little effect upon the gulls using an urban stretch of river. In particular, neither of the species causing most problems in urban areas, the Herring Gull and Lesser Black- backed Gull, decreased in number; in fact, numbers of these species nesting on buildings in the area increased considerably
Reproductive decisions in the lesser black-backed gull larus fuscus and their effects on reproductive success
No full textThe effect of several fundamental reproductive 'decisions' upon reproductive success were examined over a three year period at a large, inland gullery in the Pennines. Variations in reproductive parameters in relation to timing of breeding and reproductive success were compared among years. Determinants of the degree of hatching asynchrony were identified. Eggs from two years were taken for yolk lipid analysis, using gas chromatography. Variation in micronutrient content of eggs within clutches and between years was assessed in relation to egg size and yolk size, in order to examine resource allocation decisions of individuals. Timing of breeding of individuals was experimentally manipulated through the exchange of whole clutches of eggs between early and late laying birds, whilst controlling for variation in clutch size and egg-size, in order to assess whether the seasonal decrease in reproductive success was best explained by a decrease in food supply or differences in quality among parents. I experimentally manipulated the within-brood mass hierarchy of gulls, whilst controlling for variation in both chick quality and parental quality, in order to assess the effect of hatching asynchrony per se on chick growth and survival, and whether parents optimized the degree of hatching asynchrony with respect to the prevailing food supply. Brood size was experimentally reduced in order to assess the costs and benefits of the production of supernumary young. This was acheived by comparison of chick growth, feather development and chick survival of unmanipulated three-chick broods with broods where either the a-chick or the c- chick had been removed. I present a general discussion of the results within the context of life-history theory and a model for the evolution of hatching asynchrony in the lesser black-backed gul
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