Individually tracked geese follow peaks of temperature acceleration during spring migration

Abstract

Many migratory herbivores seem to follow the flush of plant growth during migration in order to acquire the most nutrient-rich plants. This has also been hypothesized for arctic-breeding geese, but so far no test of this so-called green wave hypothesis has been performed at the individual level. During four years, a total of 30 greater white-fronted geese Anser albifrons albifrons was tracked using GPS transmitters, of which 13 yielded complete spring migration tracks. From those birds we defined stopover sites and related the date of arrival at each of these stopovers to temperature sum (growing degree days, GDD), snow cover, accumulated photoperiod and latitude. We found that geese arrived at spring stopovers close to the peak in GDD jerk; the 'jerk' is the third derivative, or the rate of change in acceleration, and GDD jerk maxima therefore represent the highest acceleration of daily temperature per site. Day of snow melt also correlated well with the observed arrival of the geese. Factors not closely related to onset of spring, i.e. accumulated photoperiod and latitude, yielded poorer fits. A comparison with published data revealed that the GDD jerk occurs 1-2 weeks earlier than the onset of spring derived from NDVI, and probably represents the very start of spring growth. Our data therefore suggest that white-fronted geese track the front of the green wave in spring.

Migration timing and stopover selection for barnacle geese Branta leucopsis

“…The green wave hypothesis has been successfully tested for this species using direct field measurements of plant biomass and quality at selected field sites (van der Graaf et al, 2006). Moreover, the timing of the spring migration in European greater white-fronted geese (Anser albifrons) in relation to the green wave has been well predicted using peaks in the acceleration of temperature (GDDjerk), which seem to be closely related to the onset of spring (van Wijk et al, 2012).…”

“…Additionally, green wave hypothesis was tested for the Russian population of barnacle geese with the use of field data at few sites (van der Graaf et al, 2006). However, to conduct a continuous monitoring of foraging plants quality and quantity on the ground over the large migratory flyway of barnacle geese (3000-3700 km) requires intensive field work and is logically not feasible (van Wijk et al, 2012). Therefore, other substitutions have been used to depict a flush of growth or the onset of spring and assess which one of them is growing degree days (GDD) which is calculated by the summation of temperature above a certain threshold (Wang, 1960).…”

“…Therefore, other substitutions have been used to depict a flush of growth or the onset of spring and assess which one of them is growing degree days (GDD) which is calculated by the summation of temperature above a certain threshold (Wang, 1960). van Wijk et al (2012) showed that during spring migration, individual white-fronted geese followed the peaks in the acceleration of temperature (GDDjerk) which were closely related to the onset of spring and green wave of plant phenology.…”

“…To delineate stopover sites for each individual, groups of continuous GPS positions were identified where the movements of individuals between two positions in a cluster were no greater than 30 km, which is the maximum distance between resting and foraging grounds at wintering sites (van Wijk et al, 2012). The stopover sites were selected where the birds remained for at least 48 h in such a GPS cluster (Drent et al, 2007).…”

“…The stopover sites were selected where the birds remained for at least 48 h in such a GPS cluster (Drent et al, 2007). The location of each site was defined as the center of each selected group, by taking the average of the latitudes and longitudes of the GPS positions (van Wijk et al, 2012). In total, for 2008 to 2010, we recognized 57 stopover sites along the Russian flyway, 18 along the Svalbard flyway, and 14 along the Greenland flyway (for 12, 8 and 7 geese, respectively) (see Table 2.1).…”