wind and waves | 129eastern United States, caused over one billion dollars’ worth of damage
and at least 35 human deaths. At least 24 hours before the storm’s arrival
in their territories, the warblers initiated an emergency evacuation, em-
barking on a 1,500 km clockwise circuit towards Georgia and Florida.
After a five- day absence and the passage of the storm, the warblers re-
turned to Tennessee to defend their breeding territories.
This extraordinary escape behaviour begs the question of what alerted
the warblers to the approaching mayhem. One possibility is that infra-
sound, sound at frequencies below the range of human hearing,* trav-
elled outward from the tornado storms with little attenuation, and was
detected by the birds. Many bird species are known to be sensitive to
infrasound.
If small warblers have the capacity to detect approaching storms,
possibly via infrasound, possibly via changes in barometric pressure, it
would be a surprise to me if seabirds do not share the ability. This awaits
proof, but the 2nd World Seabird Conference held in the shadow of
Table Mountain learnt how, when the Category 5 tropical cyclone Pam
was rampaging in the south- west Pacific close to New Caledonia in
March 2015, frigatebirds changed their behaviour. Normally remaining
within 200 km of their colony at this season, they went 700 km away when
the storm threatened. Did they get wind of the approaching cyclone?
Doubtless there will be occasions when avoidance fails, and seabirds
become embroiled in an oceanic maelstrom. We do not know details
of how they fare but the remarkable passage of a Whimbrel through a
tropical storm gives cause for optimism. The Whimbrel was a contribu-
tor to a long- term study by Bryan Watts of Virginia’s College of William
and Mary. Using satellite tags, Watts has studied the Whimbrels nesting
around Hudson Bay and points west.^28 After breeding, the Whimbrels
face a journey to Brazil, following the eastern seaboard of the United
States and then crossing the Caribbean at a time of year when there is a
risk of encountering violent storms or hurricanes. In August 2011, one
Whimbrel named Hope encountered Tropical Storm Gert off Nova
Scotia. Undeterred, Hope entered the storm at a ground speed of about
12 km/h. Passing the eye, Hope emerged – or was ejected – 27 hours later
- (^) Infrasound has a frequency below about 20 Hz or cycles per second.