Causes of the redistribution of Pink-footed Geese Anser brachyrhynchus in Britain

The numbers of Pink-footed Geese Anser brachyrhynchus wintering in Britain have been increasing exponentially since the 1950s. The numbers of geese at virtually all roost sites have increased, but the most dramatic increase has been in Norfolk, the southernmost region occupied in Britain. This redistribution was most likely caused either by the increase in the population forcing greater numbers of geese towards more southerly sites as the result of a buffer effect, by a decrease in the quality of sites elsewhere in the range or by an increase in the attractiveness of Norfolk. Co-ordinated counts of geese around Britain and historical data of changes in agricultural practice in Norfolk were used to examine these possibilities. No evidence was found for buffer effects, degradation of sites elsewhere or an increase in food availability in Norfolk. The major difference between Norfolk and other Pink-footed Goose sites is in the food type available in Norfolk, namely harvested Sugar Beet Beta vulgaris remains. This food is of high quality and the geese are not disturbed whilst feeding on it because of its limited commercial value. The pattern of redistribution of Pink-footed Geese may therefore be the result of cultural learning of the benefits of feeding on Sugar Beet.     

Predicting the population consequences of human disturbance for Ringed Plovers Charadrius hiaticula: a game theory approach

Human disturbance and its potential impacts upon bird populations are currently topical and contentious issues for conservationists. Although many studies have revealed a behavioural impact, or even direct effect on breeding success or survival, these cannot usually be extended to predict the impact on population size. Here we present a population model that allows predictions of the effect that changes in human numbers, visiting a 9-km-long section of the coastline, may have upon the size of a Ringed Plover Charadrius hiaticula population. Human disturbance affects Ringed Plovers in our study area through birds avoiding areas of high disturbance and, in addition, through the accidental trampling of a small number of nests by people walking on the beach. Using the level of human disturbance and habitat variables (which define territory quality) it is possible to predict which areas of beach are occupied and therefore the sites available to the population. Breeding success, for a given area of beach, can be predicted from habitat data. Incorporating known, density-independent, adult mortality allows the equilibrium population size to be predicted. This provides a model that predicts population size. This model is then used to predict the population that the site would support with different, hypothetical, levels of disturbance. If nest loss from human activity was prevented, for example by fencing nests, we predict the Plover population size would increase by 8%. A complete absence of human disturbance would cause a population increase of 85%. If the numbers of people were to double, we predict the population would decrease by 23%.     

Regulation of Juvenile Hormone synthesis in the blowfly Lucilla cuprina

Abstract. Juvenile Hormone III bisepoxide synthesis by ring gland complexes from third-instar larvae of the blowfly Lucilia cuprina Weidemann (Diptera, Calliphoridae) was measured using a radiochemical assay in vitro. Hormone synthesis is regulated by three distinct mechanisms during development of the final larval instar up to the time of pupariation. The first type of regulation is detected as a rapid decline in hormone release coinciding with the final phase of commitment to pupariation. The second is a neurally mediated inhibition by the brain that acts at all stages of development in third-instar larvae. A protease-sensitive factor from brains of third-instar larvae causes dose-dependent reversible inhibition of Juvenile Hormone III bisepoxide synthesis. The third regulatory signal is a neural inhibition, observed in brain-ring gland complexes of prepupal stages. The first two levels of regulation appear to act early in the synthetic pathway for Juvenile Hormone (JH), whereas the third acts on the final steps of bisepoxide synthesis.     

Genetic analysis of resistance in Brussels sprout to cauliflower mosaic and turnip mosaic viruses

A total of 28 inbred lines of Brussels sprout were assessed in the glasshouse for their reaction to inoculation with cauliflower mosaic (CaMV) or turnip mosaic (TuMV) virus. There was significant variation for resistance to both viruses. From the 28 inbred lines parents were chosen for two 9 × 9 diallel crossing programmes. The parents and their F₁ progeny were assessed for their reaction to CaMV or TuMV in the field. There was significant additive and non-additive (dominance) variation but no maternal effects. Resistance to both viruses was generally dominant but with some evidence of a recessive gene for resistance to CaMV. Resistance to TuMV and CaMV was apparently controlled by at least four genes and two genes respectively. The heritability of resistance to each virus was high. The implications for breeding F₁ hybrid Brussels sprout cultivars are discussed.