Seasonal changes in the ventilatory response to hypoxia in migratory and non-migratory sparrows
Recent research has shown that songbirds that reside at low altitudes will ascend to ~6,000m 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 sparrow) and migratory species (song sparrow and Lincoln’s sparrow) or seasonally (during long daylight versus short daylight length) within a species. Breathing responses were tested using a stepwise reduction in inspired O2 tension (PO2), 21, 16, 12, 9, 7, and 5 kPa during long- and short-day conditions. Robust ventilatory responses to hypoxia were observed 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 by increasing breathing frequency and total ventilation, with reduced pulmonary oxygen extraction overall. Although all sparrows had similar hypoxic 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. Our findings also provide support for seasonal plasticity in the first step of the oxygen cascade, pulmonary ventilation, in migratory songbird species, which has not been well documented.