Flight Cost of a Small Passerine Measured Using Doubly Labeled Water: Implications for Energetics Studies

AI•STRACT.--Themetabolic cost of rest and activity (cm • COz'g •'h -•) was measured for the European Robin (Erithacus rubecula, 18.6 g) at temperatures (Ta, øC) from -15 to +300C.Regressions expressing these costs are: night resting (M•N) = 4.23 --0.0733Ta, day resting (Mro) = 5.10 -0.0807Ta, hopping (Mhop) = 8.60 --0.1256T•.Daily energy expenditure (DEE) for robins held in an outdoor aviary was 64.8 kJ/day (SD = 9.2, n = 6), determined using the doubly labeled water technique.This was positively related to time spent in flight (t•r, h) such that DEE = 50.9+ 23.4t•y.Flight cost for robins was estimated as 25.6 kJ/h (SD = 5.0, n = 6).This flight cost is about twice that predicted by various allometric equations.Robin flights in the aviary were short (3 m) and brief (0.78 s), indicating a mean flight speed (3.85 m/s) that was lower than the theoretical minimum power velocity (5.86 m/s).The European Robin has a relatively high wing loading (0.263 g/cm z) and aspect ratio (7.33).In a small bird with flapping flight these characteristics imply a high cost, particularly at low flight speeds.The high cost of flight was offset by its short duration.During 30-min observation periods, an average of 100.2 s was spent in flight, implying a sustained energy demand of only 3.04 kJ/h (2.7 x basal metabolic rate).The exceptionally high flight cost reported here (23 x basal metabolic rate) may be typical of short, brief aerial forays.Other doubly labeled water studies reveal a positive correlation between the time spent in flight and DEE, indicating its dominant impact on energy turnover in some free-living birds.