Meeting Abstract
Long distance migration is known to involve significant physiological changes. In the spring, birds develop their flight muscles and build considerable fat reserves to get the fuel and exercise capacity required for their journey. However, since flight muscles also play an important role in avian shivering thermogenesis, larger muscles during migration could also be advantageous for birds like the snow bunting (Plectrophenax nivalis), a passerine that faces cold conditions on arrival on its Arctic breeding ground. We investigated this potential phenomenon working with outdoor captive snow buntings during three consecutive spring fattening events. Our results show that buntings increased their body mass by more than 40% between early March and late April. This was associated with an increase of fat reserves by more than 370% and with an increase in thickness of their pectoral muscles. As expected, the birds also improved their exercise capacity and basal metabolic rate. However, as buntings begin fattening at the end of winter, cold endurance was already high and remained comparable to wintering levels throughout fattening, despite much warmer spring temperatures. Thermogenic capacity varied independently from changes in pectoral muscle size and lean mass. Our results therefore suggest that snow buntings may benefit from their migratory phenotype to face cold arrival conditions but that improving their thermogenic capacity does not require changes in muscle size.
