Frigatebirds are jerks. Or, the things you can discover when you spend a week observing the local fauna.
18 January 2015 | Isla Isabel
Vandy Shrader
Frigatebirds are jerks. They are. There's really no other way to say it. Well, actually there is another way to say it, but I don't want to use sailor words in our blog.
You might expect that someone with an education in biology ? such as myself ? would maintain more of a scientific impartiality, and would strive diligently to scrub any hint of anthropomorphism from her observations. But I'm not that person; I tend to form opinions about things that I observe, and my opinion about magnificent frigatebirds is that they are magnificent jerks.
My bird guide describes the main mode of frigatebird food procurement as ?piracy.? You could also call it ?bullying,? ?badgering,? ?harassing,? or any other synonym along those lines.
At Isla Isabel, frigatebird ?piracy? begins before the sun is up, when thousands of frigatebirds take to the sky, circling overhead in huge black vortices, watching the goings-on below them. These goings-on invariably include the foraging activities of the some of the island's other bird species ? namely blue-footed and brown boobies, and red-billed tropicbirds ? all of whom earn an honest living as fishermen, and must fly the frigatebird gauntlet upon their return.
When a blue-footed booby returns to Isla Isabel from a fishing trip, it must fly beneath the frigatebird vortex in order to reach its nest on the rocky cliffs. As soon as the booby flies over the airspace of the bay, some of the frigatebirds peel off from the flock and swoop down to give chase. The booby flies low over the water, as fast as it can, hoping to reach the relative safety of its nest before being attacked.
The frigatebirds ? which by the way are about five times as big as the booby ? come up behind the booby, and start harassing it. Sometimes the booby will land on the surface to escape the onslaught, as frigatebirds don't voluntarily alight on the water. Other times, the frigatebirds will grab the booby's tail with their beak, and jerk upward, causing the booby to crash face-first into the water.
After this rude treatment, the booby sits on the surface, watching the mini-vortex of frigatebirds that now circle in the air above it. As soon as the booby attempts to take off again, the frigatebirds swoop in, grab the booby's tail, and it again lands or crashes face-first into the water.
This process is repeated until the booby regurgitates the fish it was carrying in its stomach, at which point the frigatebirds start fighting over the goods. The booby heads back out over the ocean to catch some more fish, which it will most likely also end up feeding to the frigatebirds.
We wondered why the frigatebirds seemed to pick on the blue-footed boobies preferentially to the brown boobies. Eric may have discovered the reason: one afternoon he saw a frigatebird chasing a brown booby that was returning from a fishing trip. When the frigatebird swooped in to harass the brown booby, the booby arrested his flight momentarily, causing the frigatebird to overfly him, at which point he jabbed upward with his sharp beak, making contact with the belly of the frigatebird. The frigatebird pulled up short and flew away, abandoning the chase. Eric saw three more frigatebirds swoop in sequentially to chase the brown booby, and each time the booby repelled them with its beak-jabbing tactic.
Then the frigatebirds began to chase the speedy little tropicbirds as they left their cliffside caves to go fishing, or while they were flying around during Tropicbird Happy Hour, when they obviously didn't have any food to steal. Why? Because they're jerks.