196 research outputs found
Primary data used in Mathot, Dekinga and Piersma, Functional Ecology
No full textThe attached file includes three worksheets: 1) gizzard mass data, 2) ad libitum foraging trial data, and 3) diet choice trials. Complete descriptions of all column headings are provided on the first tab of the excel file. For details of the methodology, please refer to the original publication in Functional Ecology
Scale and intensity of intertidal habitat use by knots Calidris canutus in the Western Wadden Sea in relation to food, friends and foes
No full textIn August-October 1988-1992 we studied the distribution and abundance of knots Calidris canutus around Griend in the western Wadden Sea, and the extent to which these can be explained by benthic prey availability and presence of avian predators. Numbers in the nonbreeding season showed monthly averages of 10000 to 25000 birds. Over 100000 knots were recorded on three occasions. Knots feed in large flocks, individual birds usually experiencing 4000 to 15000 flock-mates. The Siberian-breeding/west-African wintering canutus subspecies passed through in late July and early August. Otherwise the Greenlandic/Canadian breeding islandica subspecies was present. Over the period 1964-1992 there were no clear trends in the number of knots, but canutus-knots were particularly abundant in July-August 1991, whereas in 1992 both subspecies were absent.
Macoma balthica was the preferred prey of both subspecies. Hydrobia ulvae, Mytilus edulis and Cerastoderma edule were eaten when Macoma was absent close to the surface of the sediment. As Macoma buried deeper from July onwards, canutus faced better average feeding conditions than islandica later in the year. The spatial distribution of knots feeding on the intertidal flats around Griend was best explained by the harvestable biomass of the prevalent prey species in a particular year and season, i.e. Macoma (main prey when their harvestable biomass densities were greater than ca 0.8 g AFDM per m2) and Cerastoderma, and by the avoidance of situations where they run the risk of attack by bird-eating birds. Flocks of knots covered most of the intertidal flats in the western Dutch Wadden Sea in a couple of tidal cycles. This is about 800 km2, much larger than the equivalent area used by knots on their wintering grounds in Mauritania (10-15 km2), a difference that is correlated with prey spectrum, prey availability and predictability.
Data from: An experimental test of state-behaviour feedbacks: gizzard mass and foraging behaviour in red knots
No full text1. Animals frequently exhibit consistent among-individual differences in behavioural and physiological traits that are inherently flexible. Why should individuals differ consistently in their expression of labile traits? Recently, positive feedbacks between state and behaviour have been proposed as a parsimonious explanation for the maintenance of consistent among-individual differences in both state and behaviour. If state affects behaviour, and behaviour reciprocally affects state, then even chance differences in either state or behaviour that arise among-individuals could be maintained over extended periods of time. 2. We tested for positive feedbacks experimentally using wild-caught red knots (Calidris canutus islandica). In the wild, knots exhibit consistent among-individual differences in digestive physiology (gizzard mass) and foraging behaviour (diet), two inherently labile traits. 3. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentally manipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials. 4. The effect of gizzard mass on diet choice, though in the predicted direction, was not statistically significant. Individuals exhibited consistent differences in foraging behaviour (of unknown origin) independent of current gizzard mass, as well as large residual (unexplained) variance in foraging behaviour. These sources of variation in foraging behaviour overruled the gizzard mass-dependent foraging behaviour and hence eroded the treatment-related differences in gizzard mass. 5. We conclude that positive feedbacks between diet choice and gizzard mass play at best a limited role in maintaining among-individual variation in gizzard mass in knots. Furthermore, we suggest that many models of state-behaviour feedbacks likely overestimate their potential importance in maintaining long-term among-individual variation in labile traits because they fail to account for the effects of additional factors that may act to disrupt the feedback loops. 6. The among-individual differences in diet choice observed during solitary foraging trials eroded the consistent among-individual differences in gizzard mass observed following periods of staple diet treatments in which knots foraged in social groups. As such, we suggest that social foraging interactions may play an important role determining the expression of foraging behaviours (e.g. intake rate) that themselves influence gizzard mass. Further studies are needed to experimentally test this proposed mechanism.,Primary data used in Mathot, Dekinga and Piersma, Functional EcologyThe attached file includes three worksheets: 1) gizzard mass data, 2) ad libitum foraging trial data, and 3) diet choice trials. Complete descriptions of all column headings are provided on the first tab of the excel file. For details of the methodology, please refer to the original publication in Functional Ecology.Mathot_Dekinga_Piersma_FunctionalEcology.xlsx
Hoe het nonnetje verdween uit de Waddenzee
No full textWe here describe howthe densities of Baltic tellins Macoma balthica decreased with two orders of magnitude over the last 20 years. Densities of several 100 Macoma per square meter are now very rare in this once very widespread species. Local declines have followed severe forms of habitat disturbance, notably mechanical dredging for seafood, especially cockles Cerastoderma edule.
Ultrasonic measurement of organ size in small birds to study physiological correlates:Basal metabolic rate and thermogenic capacity
No full textData from: An experimental test of state-behaviour feedbacks: gizzard mass and foraging behaviour in red knots
No full text1. Animals frequently exhibit consistent among-individual differences in behavioural and physiological traits that are inherently flexible. Why should individuals differ consistently in their expression of labile traits? Recently, positive feedbacks between state and behaviour have been proposed as a parsimonious explanation for the maintenance of consistent among-individual differences in both state and behaviour. If state affects behaviour, and behaviour reciprocally affects state, then even chance differences in either state or behaviour that arise among-individuals could be maintained over extended periods of time.
2. We tested for positive feedbacks experimentally using wild-caught red knots (Calidris canutus islandica). In the wild, knots exhibit consistent among-individual differences in digestive physiology (gizzard mass) and foraging behaviour (diet), two inherently labile traits.
3. Experimentally manipulated diet quality had a large effect on gizzard mass. Experimentally manipulated gizzard mass reciprocally influenced total food eaten during ad libitum trials.
4. The effect of gizzard mass on diet choice, though in the predicted direction, was not statistically significant. Individuals exhibited consistent differences in foraging behaviour (of unknown origin) independent of current gizzard mass, as well as large residual (unexplained) variance in foraging behaviour. These sources of variation in foraging behaviour overruled the gizzard mass-dependent foraging behaviour and hence eroded the treatment-related differences in gizzard mass.
5. We conclude that positive feedbacks between diet choice and gizzard mass play at best a limited role in maintaining among-individual variation in gizzard mass in knots. Furthermore, we suggest that many models of state-behaviour feedbacks likely overestimate their potential importance in maintaining long-term among-individual variation in labile traits because they fail to account for the effects of additional factors that may act to disrupt the feedback loops.
6. The among-individual differences in diet choice observed during solitary foraging trials eroded the consistent among-individual differences in gizzard mass observed following periods of staple diet treatments in which knots foraged in social groups. As such, we suggest that social foraging interactions may play an important role determining the expression of foraging behaviours (e.g. intake rate) that themselves influence gizzard mass. Further studies are needed to experimentally test this proposed mechanism
Disturbance of Foraging Knots by Aircraft in the Dutch Wadden Sea in August-october 1992
No full text
Hoe het nonnetje verdween uit de Waddenzee
No full textWe here describe howthe densities of Baltic tellins Macoma balthica decreased with two orders of magnitude over the last 20 years. Densities of several 100 Macoma per square meter are now very rare in this once very widespread species. Local declines have followed severe forms of habitat disturbance, notably mechanical dredging for seafood, especially cockles Cerastoderma edule
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