Seasonal changes in the daily energy budgets of migratory geese at a spring stopover site estimated from telemetry data

Background/Question/Methods

The spring migration is regarded as an energetic bottleneck in the annual cycle of capital breeders because they must accumulate energy and nutrients in preparation for further migration and breeding. Furthermore, because of seasonality in availability and quality of food recourses in staging areas, each stopover site offers a different set of constraints. En route to their breeding grounds, the Svalbard population of pink-footed geese stops twice, in mid- and northern Norway. Each stopover site provides different combinations of energy-rich and nutrient-rich resources. The aim of this study is to calculate the metabolizable energy intake of geese in mid Norway – the last site at which both resource types are present.  The estimation of the daily energy budget was based on GPS tracking of individual birds and activity budgets derived from flock scans. 

Results/Conclusions

The daily metabolizable energy intake was positive for all individuals and on average geese gained 1.6 more energy than they spent. However, the daily metabolizable energy was still below the maximum daily fuel deposition rate calculated for the studied species, which could be due to digestive constraints, food availability and the increased cost of flying with increased body mass. In mid-Norway habitat use by the geese was not proportional to habitat availability, and variations in energy intake were not related to the relative availability of resources with different energetic content and digestibility and the time available for feeding.  Energy intake on a given day was correlated to the energy intake in the previous days. This trend was the same throughout the stopover season suggesting that foraging behaviour is a chain of decisions taken on a daily basis, although overall energy intake probably mediates decision-making. The total metabolizable energy intake was correlated with the time spent at the studied site. We conclude that mid-Norway does not currently serve as an energetic bottleneck, although the increased flying costs due to frequent disturbance and increased energy expenditure due to intra- and inter-specific competition may alter this situation in the future.