Movements of a nomadic waterfowl, Grey Teal Anas gracilis, across inland Australia – results from satellite telemetry spanning fifteen months

We used lightweight satellite transmitters to follow the movements of 17 Grey Teal Anas gracilis between September 2003 and November 2004 in two contrasting landscapes, the agricultural districts of southern Australia and the desert landscapes of the interior. Tagged birds moved large distances (up to 343 km) between occupied sites in a short period (hours), remained in the vicinity of those sites for extended periods (months), ventured up to 453 km from their point of release and travelled more than 2000 km in one year. We describe patterns of movement in a nomadic waterfowl for 15 months from September 2003, a period of severe drought. Based on the current analysis there appears to be no remarkable difference in the observed patterns of movement of those released in the agricultural landscapes and those released in the desert. As in waterfowl elsewhere, movements appear to occur in response to changes in local food abundance that threaten survival or the imperative to move in order to breed successfully. In Grey Teal, the proximate cues for movement transcend the local landscape and some birds are responding to temporary cues hundreds of kilometres distant. This is in contrast to the universal seasonal cues associated with migration systems elsewhere.

Why do Gull-billed Terns Gelochelidon nilotica feed on fiddler crabs Uca tangeri in Guinea-Bissau?

Gull-billed Terns Gelochelidon nilotica wintering in Guinea Bissau mainly fed on fiddler crabs Uca tangeri and were occasionally seen feeding on fish and locusts. As fiddler crabs have a low energy content, terns need a large gross intake to meet daily energy demands. Fiddler crabs also have a low ratio of digestible flesh to exoskeleton, and therefore tern food intake may be limited by gut capacity. Activity budgets of Gullbilled Terns feeding on fiddler crabs showed that a considerable part of the time was spent resting. The duration of resting intervals increased with energy intake and was positively correlated with the metabolisable energy content of the crab eaten, suggesting that resting periods were required for a proper digestion. The poor quality of fiddler crabs was offset by high capture rates. So daily energy expenditure of the terns could easily be met by feeding on fiddler crabs. Even when resting pauses were included in foraging time, foraging for only 1.5 hours on fiddler crabs satisfied the terns’ daily energy demands. Instead, feeding on energy-rich fish would require about 2.5 hours to satisfy daily energy demands. Compared to the more specialised piscivorous Little Tern Sternula albifrons and Sandwich Tern Sterna sandvicensis, capture rate of fish was poor in Gull-billed Terns. From an energetic point of view, wintering Gull-billed Terns feeding on fiddler crabs seem to have an easy living in Guinea Bissau.

Intake rates, stochasticity, or onset of spring : what aspects of food availability affect spring migration patterns in Pink-footed Geese Anser brachyrhynchus?

Long-distance bird migration consists of several flight episodes interrupted by a series of resting and refuelling periods on stopover sites. We assessed the role of food availability as the determinant of staging decisions focusing on the following three aspects of food availability: intake rates, stochasticity in intake rates and onset of spring. Using stochastic dynamic modelling, we investigated their impact on staging times and expected fitness. Subsequently, we compared relations in the use of the stopover sites as predicted by the model with empirical data of the Svalbard-breeding population of Pink-footed Goose Anser brachyrhynchus collected in the period 1990–2002. Our results indicate that, for the case of Pink-footed Geese, spring phenology determines a major part of the migration schedule. In contrast to our expectations, intake rates were generally only of minor importance; however, when approaching the breeding grounds their significance increased. Expected fitness at arrival on the breeding grounds showed that the geese can compensate for changes in a broad range of food availability and also cope with varying degrees of stochasticity. However, declining intake rates at the last stopover site or very late onsets of spring clearly decreased fitness. As predicted by the model, the use of stopover sites was interdependent – from empirical data we derived negative relationships between the staging durations of subsequent sites. These results lend credit to an integrated spatially explicit approach focussing on multiple stopover site characteristics when attempting to improve our understanding of bird migration.

Factors affecting the site of investment, and the reliance on savings for arctic breeders : the capital–income dichotomy revisited

The extent to which migratory birds that breed in the Arctic and winter in southern biomes rely on residual body stores for reproduction is unresolved. The short arctic summer and the limited availability of food early in the season constrain the time available for successful reproduction. Birds that are able to bring sufficient endogenous reserves to the breeding ground to meet, at least partially, the demands of egg-laying can initiate clutch production soon after arrival, thereby shortening the length of the breeding season and improving the chances of reproductive success. The amount of reserves available will be influenced by body size, the increased energetic and predation costs associated with carrying large stores, distances between staging sites and the location of the breeding grounds within the Arctic. Birds need not fly directly to the breeding grounds from the established temperate staging sites. Extensive feeding by migrants may occur in the Arctic, even within a few kilometres of the breeding sites as the birds track the retreating snowline. Irrespective of their size, birds are thus able to store some resources necessary for egg laying at local or regional scales. It is thus important to make a distinction between local capital and distant capital breeding. The extent to which a bird is characterized as a distant capital, local capital, or an income breeder not only varies between species, but also between individuals and seasons.

A new interval-based method for handling non-monotonic information

The focus of this paper is on handling non-monotone information in the modelling process of a single-input target monotone system. On one hand, the monotonicity property is a piece of useful prior (or additional) information which can be exploited for modelling of a monotone target system. On the other hand, it is difficult to model a monotone system if the available information is not monotonically-ordered. In this paper, an interval-based method for analysing non-monotonically ordered information is proposed. The applicability of the proposed method to handling a non-monotone function, a non-monotone data set, and an incomplete and/or non-monotone fuzzy rule base is presented. The upper and lower bounds of the interval are firstly defined. The region governed by the interval is explained as a coverage measure. The coverage size represents uncertainty pertaining to the available information. The proposed approach constitutes a new method to transform non-monotonic information to interval-valued monotone system. The proposed interval-based method to handle an incomplete and/or non-monotone fuzzy rule base constitutes a new fuzzy reasoning approach.