Seasonal changes in the ventilatory response to hypoxia in migratory sparrows and an introduced resident sparrow

Recent research has shown that songbirds that reside at low altitudes can ascend to ~6,000 m above sea level during migratory flight. Since migratory flight is aerobically demanding, whether migratory songbirds exhibit plasticity in breathing to maintain oxygen uptake in low-oxygen environments is unknown. This study investigated whether the hypoxic ventilatory response of sparrows was altered between resident house sparrows (Passer domesticus, Linneaus, 1758) and migratory song sparrows (Melospiza melodia, Wilson, 1810), and Lincoln’s sparrows (Melospiza lincolnii, Audubon, 1834) or seasonally (long daylight versus short daylight length) within a species. Breathing responses were assessed by stepwise reductions in inspired O2 tension, 21, 16, 12, 9, 7, and 5 kPa during long- and short-days. Ventilation increased in hypoxia in all species, although song sparrows and Lincoln’s sparrows exhibited greater increases in ventilation in severe hypoxia compared to house sparrows. All species became more sensitive to hypoxia during short days compared to long days (increased breathing frequency and total ventilation), with reduced pulmonary oxygen extraction. Although all sparrows had similar ventilatory responses in moderate hypoxia, our findings suggest that migratory sparrows breathe more effectively in severe hypoxia compared to house sparrows, which would be important for maintaining oxygen uptake during migratory flights.