Authors: Catherine M. Ivy* and Christopher G. Guglielmo
Year: 2023
Publication: Journal of Experimental Biology
Publication Link: https://journals.biologists.com/jeb/article/226/17/jeb245975/326576/Migratory-songbirds-exhibit-seasonal-modulation-of
Keywords: Control of breathing, Haematology, Muscle morphology, Thrushes, Warblers, Vireos
Abstract: Migratory flight requires birds to maintain intensive aerobic exercise for
many hours or days. Maintaining O2 supply to flight muscles is
therefore important during migration, especially since migratory
songbirds have been documented flying at altitudes greater than
5000 m above sea level, where O2 is limited. Whether songbirds
exhibit seasonal plasticity of the O2 cascade to maintain O2
uptake and transport during migratory flight is not well understood.
We investigated changes in the hypoxic ventilatory response,
haematology and pectoralis (flight) muscle phenotype of 6 songbird
species from3 families during migratory and non-migratory conditions.
Songbirds were captured during southbound migration in southern
Ontario, Canada. Half of the birds were assessed during migration,
and the rest were transitioned onto a winter photoperiod to induce a
non-migratory phenotype and measured. All species exhibited
seasonal plasticity at various stages along the O2 cascade, but not
all species exhibited the same responses. Songbirds tended to be
more hypoxia tolerant during migration, withstanding 5 kPa O2 and
breathed more effectively through slower, deeper breaths. Warblers
had a stronger haemoglobin–O2 affinity during autumn migration
(decrease of ∼4.7 Torr), while the opposite was observed in thrushes
(increase of ∼2.6 Torr). In the flight muscle there was an ∼1.2-fold
increase in the abundance of muscle fibres with smaller fibre
transverse areas during autumn migration, but no changes in
capillary:fibre ratio. These adjustments would enhance O2 uptake
and transport to the flight muscle. Our findings demonstrate that in the
O2 cascade there is no ideal migratory phenotype for all songbirds.