Energetics and Time Allocation of Cackling Canada Geese during Spring

We compared the observed daily time allocation of cackling geese (Branta canadensis minima) during spring with that predicted from estimates of daily energy requirements and measurements of apparent metabolizable energy (AME) and intake rates. Cackling geese gained substantial energy and protein reserves at staging areas in California before migration to Alaska in April and after arrival in Alaska, before egg laying. Cackling geese gained mass during spring by increasing intake rates (g/hr) and by feeding more during the evening and night. During March and April, cackling geese spent 10-12.6 hr each day on feeding fields. We estimated that while cackling geese are on feeding fields they must eat on average 11–18 g dry mass/hr in March and 18–20 g dry mass/hr in April to satisfy daily energy requirements. Diet quality affected intake rates and the amount of time geese spent grazing. When cackling geese were fed a lower-quality forage (pasture grass) they ate 50% less than geese fed a higher-quality forage (alfalfa). AME of the 2 diets was similar (11.3 kJ/g and 10.9 kJ/g). Cackling geese in the wild spent more time feeding when in pasture compared to alfalfa fields, apparently to compensate for reduced intake rates. Temperature had little effect on time allocation except when below -6° C. Compared to larger herbivores, small grazers like cackling geese must eat proportionately more each day and are more likely feeding-time limited. The feeding time of cackling geese during spring was limited primarily by predation risk, daylength, and harvesting and digestive constraints associated with selectively eating leaves.