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Most studies of energetics in marine filter feeders have focused on animals living in steady state food conditions. However, copepods experience highly variable access to food because of food patchiness and behavioural avoidance of predators. For small copepods this is especially important since they lack the potential of energy storage, e.g. in the form of lipids. After a period of food deprivation Acartia tonsa show a compensatory increase in ingestion rate, but only temporarily and on the time scale of the gut filling time. The copepods are able to compensate for the lacking input of food. On the other hand, longer periods of starvation (6-14h) induce elevated ingestion rates that lasts longer than gut filling time. Under these circumstances other energetic factors influence the ingestion rate. Consequently, the energetics of the copepods are highly variable in a patchy food environment.
Large numbers of birds breed each summer on the tundra of the northern hemisphere. Two prominent groups in the Arctic bird fauna are waders and waterfowl (ducks, geese and swans). Breeding, which is an energetically costly activity (Drent & Daan 1980), is especially costly in the high Arctic. This is mainly due to low temperatures and high wind speeds in an open landscape (Piersma & Morrison 1994, Wiersma & Piersma 1994). In addition, the summer period is very short. This leaves little time for necessary pre-breeding, breeding and post-breeding activities. Thus, costs are high and available time is short. In order to reach their breeding grounds, arctic birds have to migrate over vast distances between their Arctic breeding sites and temperate or tropical wintering grounds. Migration is also an energetically costly event. This generally high rate of living puts high demands on the birds and we may expect the birds to have evolved a wide range of physiological and behavioural adaptations. Given the inaccessibility of most tundra areas and the necessity of relatively advanced techniques, ecological energetic studies of wader and waterfowl are relatively scarce (with the notable exception of tundra breeding Nearctic geese). With this project we aim at measuring and describing some important energy turnover processes of waders and waterfowl during the short and hectic Arctic summer and to evaluate them in an evolutionary context. We will pay particular attention to the importance of energy and nutrient stores with which the birds arrive at the breeding grounds for egg production, energy turnover of breeding birds in relation to species and microclimate, and the fat deposition and basal metabolism of birds preparing for autumn migration. The project is partly a continuation of work carried out during the Swedish-Russian Tundra Ecology Expedition 1994 (TE-94). Research activities: Capital vs. income breeders Since the favourable season is short for Arctic breeding birds, they are hard pressed to start egg laying immediately after arrival at the breeding grounds. However, upon arrival food availability is often low. It is thought that female birds planning to start a family on the tundra are forced to produce a clutch using, at least to some degree, body reserves accumulated prior to or during their migratory journey. Birds using such a strategy are called capital breeders, in contrast to income breeders' that only use resources obtained during the reproductive period (Drent & Daan 1980). We seek to investigate how commonly the capital breeder strategy is on the Nearctic tundra and how its use varies with: - Species: large species are expected to be more dependent on this - Strategy as their breeding seasons are longer and they are thus more time stressed. - Site: birds at sites where circumstances allow an early start of the breeding season may not be equally dependent on capital breeding than birds using late sites. - Timing: early arriving birds are more pressed to use the capital breeding strategy than late arriving birds, the latter being able to produce eggs from the food available upon arrival. The different potential food sources to birds often have distinct isotopic ratios of C12/C13 and N14/N15 depending on environment and metabolic characteristics. Isotopic ratios of C and N can therefore serve as a kind of fingerprint for these food stuffs. These specific ratios will ultimately also be reflected in the isotopic composition of the consumers tissues; especially with regard to C12/C13 ratios (Hobson & Clark 1992). Distinct differences may therefore also be expected in tissue isotope ratios of newly hatched young from capital and non-capital breeders. Such differences may also appear within nests in case the female has used a mixed strategy. Although in developing tissues these differences may rapidly fade away, isotope differences between young may be fixed in down feathers already present at hatching. Comparing the isotope ratios in down samples within broods with isotope ratios in potential food sources at the breeding ground thus provides a clue to the extend the mother made use of the capital breeding strategy. We will collect down, feathers and blood from all birds trapped. We will concentrate on waders, yet, also waterfowl are of high interest (although the chances to trap birds are smaller). Of highest priority will be down from chicks and blood from parent birds. In likely foraging areas of parents and chicks that we have sampled, we will collect insects and plants and other possible food sources. At the NIOO the samples will be analysed for C12/C13 and N14/N15 ratios using mass spectrometry. The fact that we will visit many different habitats with different climate, foraging conditions and phenology is a major prerequisite for successfully conducting this part of the project. Energy turnover of brooding birds The few available measurements of daily energy expenditure (DEE) of incubating waders in tundra regions, using the doubly labelled water (DLW) method, have shown that breeding in the High Arctic is indeed costly (Piersma & Morrison 1994, Piersma et al. unpublished data from Siberia). The high cost stems from the combined effects of low temperatures and high wind speeds in an open landscape, but may also be affected by the birds own intense foraging activities. However, the measurements that have become available up till now do not cover the whole "climate space" that arctic breeding waders encounter, due to the bias in study sites and the particularities of weather conditions during the few studies that have been carried out. We would like to extend the series of measurements using DLW in incubating waders of more species than hitherto available and under more environmental conditions. Field measurements of DEE involve initial capture of a bird on the nest, loading it with DLW and recapturing the bird after a certain period of time, usually 24-48 hours. There is room for improvement over the earlier studies in monitoring the loaded birds activity budget (using transponders, small radiotags and/or nest/egg temperature recorders) and in assaying the birds physiological status. Apart from mass and size variable, birds could probably be assayed for the thickness of the breast muscle (a heat generating part of the body) and the size of the stomach (as an indicator of the digestive apparatus) using ultrasound. These techniques are under development at NIOZ and the University of Groningen at the moment. Equally, body composition in terms of fat and lean components could be estimated from dilution factors after quantitative DLW injections. It is crucial to simultaneously measure the meteorological variables air temperature, wind speed and global solar radiation, and hence a weather station has to be brought to the study sites to this effect. Fat deposition and basal metabolism of birds preparing for autumn migration Waders need high-performing bodies to cope with their energetically high rate of living. This is reflected in their basal metabolic rate (BMR). The BMR of an animal is the energy it spends at rest (i.e., at night for day-active animals), in thermoneutral conditions, without processing food, and when it is not involved in productive activities like reproduction, moult or growth. The BMR of a bird may be compared with the fuel consumption of a car engine that is running idle. A Formula-One car, that operates at an incredibly high rate also has a high cost of running idle. A standard car with a less impressive engine takes less energy to keep running. As the cost of running idle reflects the potential power of an engine, the BMR reflects the potential rate of work of an animal body. Waders have comparatively high BMR compared to other non-passerine birds (Kersten & Piersma 1987). Moreover, studies of captive Knots have shown that they vary their BMR over the year (Piersma et al. 1995). In addition, waders trapped during the first part of their autumn migration in Arctic Eurasia were found to have higher BMR than their conspecifics at tropical wintering grounds in Africa (Kersten et al. in press, Lindström in press a). This all suggests that waders can adjust the size of their engine which makes sense, since the best solution would be to have a strong engine when circumstances so demand, and a smaller engine during more relaxed parts of the year (for example at wintering grounds in Africa; Klaassen et al. 1990). Although we are actually most interested in the long-term maximum rate of energy expenditure as a measure of adaptations to a high rate of living, this is very difficult to measure, and especially so in a comparable way. Instead, the BMR, which is supposed to reflect the maximum energy turnover potential, is fairly easy to measure, and figures from different investigations can be compared. During TE-94, 24 juvenile waders of five different species were measured for their BMR in a respirometer (Lindström in press a). We want to continue this work by including birds of new species, and of the same species but from another breeding area. Juvenile birds will be caught during the first parts of the autumn migration (mainly August) in portable and walk-in traps. They are then brought to the ship where they will be measured in the respirometer. The BMR values will be compared to those obtained during TE-94 and with data from the migration and the wintering grounds in America and Europe to look for inter- and intra-specific patterns. Whereas it is fairly well known that many (most ?) wader species put on huge energy reserves prior to migration to the Arctic, almost nothing is known about the size of reserves carried by waders prior to departure from the Arctic. This is necessary to know in order to understand the migration strategies adopted (Alerstam & Lindström 1990) and when analysing migration routes. During TE-94 almost 300 juvenile waders were trapped during August, most of them being Little Stints Calidris minuta. It was revealed that also when migrating from the Arctic, substantial energy reserves were put on (Lindström in press b). We now want to collect corresponding data from the Nearctic. Whereas much is known about the size of energy reserves of migration waders further south in America (for example, McNeil & Cadieux 1972, Thompson 1974, Johnson et al. 1989, Driedzic et al. 1993), we know of no such data from the Nearctic region.