EFFECT OF WIND ON FIELD METABOLIC RATES OF BREEDING NORTHERN FULMARS

The field metabolic rate (FMR) of nesting Northern Fulmars (Fulmarus g lacialis) was measured using the doubly labeled water technique. Altho ugh some labeled Northern Fulmars showed marked differences in behavio r compared to controls, FMR did not change correspondingly. At-sea FMR averaged 1444 kJ/d, equivalent to 4.5 x basal metabolic rate (BMR). A s a multiple of BMR it was independent of sex, wing length, body mass, mass change, and duration of the period at sea, but was strongly depe ndent on wind speed, being higher during slack winds. There was also a trend for higher wingbeat frequency at winds too low for sustained dy namic soaring. The high energetic cost of flapping flight during windl ess conditions may explain patterns of nest attendance: in particular, why nest site attendance by Northern Fulmars in winter is greater dur ing calm weather. Lack of wind might limit the breeding range of this species and other Procellariiformes with high flapping-flight costs.