Long-distance migration is a biannual athletic feat for many birds. It's a grand physical test that plays out across hundreds or thousands of miles, and a display of endurance that to us humans would be mind-boggling undertaken even once, just one-way – let alone round-trip each and every year. Migratory mishaps are all too common, and as in the case of one unlucky vulture off the Spanish coast, they can leave a bird flailing for its life.
For a huge soaring bird such as the Eurasian griffon vulture – which spends most of its time on the wing taking advantage of those handy rising air currents called thermals – an out-and-back journey poses a particular challenge. Griffons trying to cross over from North Africa to Europe over the Mediterranean Sea funnel above the narrow chokepoint of the Strait of Gibraltar, but even that 14-kilometre (~9-mile) crossing places heavy demands on the vultures' inflight abilities.
One griffon this spring didn't quite make it across the big blue, and ended up adrift in the Mediterranean chop. A dicey situation, we should note, for a bird that flaunts wings nine feet across and may weigh more than 20 pounds.
Juan Ramirez, who has monitored Strait of Gibraltar raptor migration since the late 1990s, captured photographs of the huge downed bird in May, and the snaps were later posted to Facebook by the Mediterranean Raptor Migration Network (MEDRAPTORS).
The vulture ended up in the water after being harassed by gulls, a common misery for continent-crossing raptors. Ramirez says griffons, short-toed eagles, booted eagles and sparrowhawks seem most vulnerable to this indignity. "Every season we witness how many of these raptors, after being chased over the sea, fall down on the water and drift with the stream till dead," he said in an email.
Ramirez and some of his colleagues took it upon themselves to track the springtime vulture migration over the Mediterranean bottleneck this spring, even though funding has prevented that undertaking in recent years. Thanks to their dedication, we know some 6,200 Eurasian griffons plus a quartet of Rüppell's griffons arrived on these European shores from Africa this season.
And it's not just gull-mobbing that troubles the biggest raptors in their trans-Mediterranean voyages. Griffons, like most vultures, are not particularly strong fliers – although thanks to their thermal-riding prowess, they're downright magnificent in the soaring department. Straight-line crossings over seawater, however, present a stiffer challenge.
A study of the autumn migration of griffons over the Mediterranean showed just how taxing even the relatively short flyover of the Strait of Gibraltar can be. The vultures attempted the journey only under calm conditions or favourable winds. They flapped ten times as much over water as over land, and if their flapping got out of control (specifically, 20 flaps per minute or more), the birds usually pulled a 180 and returned to the shore they'd disembarked from. More than a few griffons end up drowning in the attempt.
"Our observations indicate that passage of griffon vultures at the Strait of Gibraltar is limited by the species' over-water flapping-flight abilities," the authors of that study wrote, "including inability to flap continuously for even short periods of time."
This particular griffon, fortunately, beat the odds and managed to breaststroke its way to shore. "[This is] something really rare," Ramirez noted. The following morning, he and his fellow observers saw the waterlogged vulture perched on a cliff, before the bird flew away with no apparent ill effects from its briny bath.
__
Top header image: Juan Ramirez
Sharks
Animal Behaviour
Animal Behaviour
