Theoretical predictions of the influence of infection on movement metrics. If infection affects spatial behaviour, infected (blue) and uninfected (red) birds should behave differently at the time of release. We postulate that, at this time, movement metrics for infected birds should be lower than for uninfected birds, which would be revealed as different intercepts of the regression of the movement metrics against time for uninfected (β0) and infected birds (β0+βInf). As infected birds recover with time, their movement metrics will approach and eventually meet the values for uninfected birds. This happens when the slope of the regression of the movement metrics against time for infected individuals (βT.aft.Rel*inf) reaches the slope for uninfected birds (βT.aft.Rel), which is expected to be null.
Examples of different types of movement behaviour in autumn-staging mallards for (a) ‘trap-dependent’ (i.e. returning to the trap) and (b) ‘trap-independent’ (i.e. not returning to the trap) individuals. T marks the location of the duck trap.
Movement metrics used in the analyses, their significance and abbreviations.
total cumulative distance travelled
the total sum of the lengths of the recorded trajectory measured in metres using great circle distances between all consecutive recorded locations
maximum displacement or the maximum distance between any two locations the birds were observed
mean of all step lengths measured in metres from consecutive locations
mean of the step length in metres divided by the time lag in seconds
maximum value of distance covered between two locations divided by time
mean coefficient of the first passage time (FPT)
the FPT measures the time an individual needed to cross a circle of a given radius r. It is a cross-scale analysis of the movement pattern, where the slope of the log of the mean of FPT against the log of the radii of the circles should be about 2 for Brownian motion. Lower values indicate facilitated diffusion, or subdiffusive or advective movement, referring to non-random and thus, more or less, directional movement. Higher slopes indicate superdiffusive or impeded diffusion
intercept of the mean FPT
the intercept of the correlation of the log of the radii and the FPT is an indicative of the most basal movement characteristic, or the tendency to move irrespective of scaling effects (innate movement)
dispersion factor of a Brownian bridge based on the trajectory
movement can be described by a conditional Brownian motion where an animal moved between known locations in a conditional Brownian fashion, corresponding to a two-dimensional Gaussian process, with a certain variance or dispersion factor (h). The higher the estimated variance, the more erratic the movement was and more deviance around the straight line connection is to be expected
area of a minimum convex polygon
the area that the animal used according to a minimum area polygon containing all observed locations
Average overall dynamic body acceleration (ODBA) values (covering maximum 7 days) for infected versus uninfected mallards. A higher value stands for a higher amount of body movements. If a recaptured individual had changed infection status, it was counted as a new ODBA event. In total, 87 ODBA events were obtained from 37 mallards.
Average total cumulative distances (Dtot in m), mean speed between two consecutive locations (vseg in m s−1), minimum convex polygon area (MCP in ha) and sample size (n, number of locations) during day/night and for each of the mallard categories during the first 7 days after sampling. trapd, trap-dependent individuals; ntrap, trap-independent individuals.
Dtot (95% CI)
vseg (95% CI)
MCP (95% CI)
Mean regression coefficients (β)±s.e. of the model log(Mov.metric) = Inf + T.aft.Rel + Reloc + Behtrap + DN + Inf*T. aft.Rel for total cumulative distance (Dtot), mean speed between consecutive locations (vseg) and MCP in the first 7 days after sampling. Only coefficients describing the effect of infection are shown, i.e. β0 the intercept for uninfected mallards, βinf the intercept difference between infected and uninfected individuals, βT.aft.Rel the slope quantifying the movement metric evolution after release in uninfected mallards, and βInf*T.aft.Rel the slope difference between infected and uninfected individuals. P-values are indicated in brackets and significant values are in bold.