DOI: 10.5061/dryad.k28j0
title: Data from: An experimental test of state-behaviour feedbacks: gizzard mass and foraging behaviour in red knots

description: 1. 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.
description: 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