Kersten M., Bruinzeel L.W., Wiersma P. & Piersma T. (1998) Reduced basal metabolic rate of migratory waders wintering in coastal Africa. ARDEA 86 (1): 71-80

We measured Basal Metabolic Rate (BMR) of 16 wader species (order Charadriiformes) on their wintering grounds in Africa. The allometric regression equation relating BMR to body mass: BMR (W) = 4.02 x M (kg)0.724 runs parallel to that of waders in temperate areas, but at a 20% lower elevation. Since waders wintering in the tropics have a reduced body mass, the difference in BMR between members of the same species at tropical and temperate latitudes was even larger and amounted to 31%. BMR did not differ between families nor did it differ between long-distance migrants that breed in the Arctic and species that spend their entire life in the tropics. As migrant waders have a higher BMR during autumn migration in the north, we suspect that they reduce BMR upon arrival in the tropics. We hypothesize that this reduction is due to somatic factors under control of hormonal factors, including a reduction of organ sizes and probably suppressed thyroid activity induced by the high ambient temperatures in the tropics. The involvement of thyroid hormones in the regulation of BMR would be consistent with the fact that waders in the tropics regulate their body mass at a lower level than birds in temperate areas and may explain why the rate of premigatory fattening is slower in the tropics than further north. The mechanism, a dual control system including somatic and hormonal factors acting in concert, rapidly adjusts BMR of migratory waders to the different ecological conditions encountered during their long journeys to and from the breeding grounds