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In 1990, we investigated a die‐off of freshwater mussels in north‐central North Carolina. An estimated 1,000 mussels of several species were found dead or moribund, including about 111 Tar spinymussels (Elliptio steinstansana) a federally listed endangered species. The die‐off occurred during a period of low flow and high water temperature in a stream reach dominated by forestry and agriculture. Pathological examinations did not show any abnormalities and indicated that the die‐off was an acute event. Chemical analyses of mussels, sediments, and water revealed no organophosphorus or carbamate pesticides. Cholinesterase activity in adductor muscle from Eastern elliptios (Elliptio complanata) collected at the kill site and downstream was depressed 73 and 65%, respectively, compared with upstream reference samples. The depression is consistent with a diagnosis of anticholinesterase poisoning. This is the first documented case in which cholinesterase‐inhibiting compounds have been implicated in a die‐off of freshwater mussels.

A wide variety of topographical and environmental elements have been shown or proposed to influence the movement decisions of dispersing animals. Most real landscapes have topographical elements such as hills, valleys and urban developments, which can all act to modify a species' perceptual range and directly influence movement behaviour. If a visual-based perceptual ability enables a dispersing individual to locate suitable habitat patches at a distance, then it is to be expected that topographical features would act to modify the overall success of this strategy. However, the majority of individual-based Spatially Explicit Population Models (SEPM) employ only two-dimensional landscapes.To investigate the effects of topographical elevation on dispersal patterns, a threedimensional visual-based perceptual range algorithm was added to the dispersal rules of an individual-based SEPM. To explore the possible influences of a behaviouralbased response to topography, an algorithm modelling valley-seeking behaviour was also developed. The performance of both algorithms was compared with that of a twodimensional visual-based perceptual range algorithm. The overall consequences of

Factors such as early fledging and natal territory location have been shown to influence dispersal and settlement success of woodland birds. Early fledging allows for earlier dispersal, increasing the chances of an individual locating good quality habitat. However, for birds in fragmented woodland, the advantages of early dispersal may be modified by natal territory location in relation to the availability of suitable habitat in the surrounding landscape. Connecting habitat corridors may promote dispersal, and connectivity in landscapes is usually considered as positive, but this may not always be the case. In landscapes where habitat is highly fragmented, corridors may promote departure, but leave dispersers with little chance of success.An individual-based Spatially Explicit Population Model was used to investigate the effects of timing of fledging, natal territory location and proximity to potential dispersal corridors on local settlement rates. Modelling was based on both hypothetical and real woodlands and used marsh tit as an example woodland bird. For each modelled scenario, the number of young that settled was recorded for each territory, the overall results being expressed as the mean percentage settlement rate per territory.Territory location and edge effects were both found to influence dispersal and settlement rate. Fledging early clearly demonstrated a general advantage for local settlement success. However, territory location, in relation to the likelihood of dispersing out of the wood was found to interact with fledging order. Fledglings from internal territories had an advantage over those from edge territories and local settlement rate could be reduced by a location favourable to emigration. In general, the effect of exits was to reduce the settlement rate of early fledging young while that of later young tended to increase. In highly fragmented woodland, fledging late from a well-connected edge territory would appear to be the worst case scenario.

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