Imagine that you just picked up lunch at the drive-through window. Then, just as you’re about to take that first bite at a stop light, someone whizzes by and grabs your burger right out of your hand. Then someone else comes up on the other side and scares you so much you drop your fries, which they grab. This is not a hypothetical situation if you are a tern on Cape Cod right now, it is a daily nightmare.
September is prime time to watch the hamburglars of the sea robbing terns at beak-point and stealing their hard-earned fish. The perpetrators are seabirds called jaegers, and they are pretty fun to watch if you’re not a tern. Terns, of course, are the delicately built, hard-working seabirds who are currently here to fatten up for a flight to wintering grounds in West Africa or Brazil. Unlike their larger, trash-eating cousins the gulls, terns stick to a healthy diet of fish, shrimp, and a few insects. They catch all their own food and wouldn’t be caught dead with a French fry.
But sadly, terns are frequent victims of what biologists have named kleptoparisitism, which means “stealing grub from other creatures” in fancy science talk. Around here we see kleptoparasitism in practice when eagles steal fish from Ospreys and when gulls steal food from everyone, including you at the beach that one time. Jaegers are the best-known practitioners on the oceans. Three species ply our waters – Parasitic, Pomarine, and Long-tailed. All look like dark gulls to the uninitiated, I suppose, but they “hit different” as the kids say – jaegers seem faster and more athletic even when they’re not in a hurry. Pomarines are relatively bulky brutes and Long-taileds more slightly built, but these differences are subtle and identifying jaegers is hair-pullingly difficult, even for seasoned birders.
Both Pomarine and long-tailed depend completely on lemmings during breeding season in the Artcic, and if there are no lemmings in any given year, they give up and head back out to sea. Parasitic Jaegers, the ones we see most, aren’t so picky when nesting, feeding on other birds and their eggs, as well as rodents, plus they rob other seabirds of their fish in breeding season, too. All the jaegers head south to spend the winter scavenging meals or stealing food from southern hemisphere seabirds.
Parasitic Jagers are by far the default species here. Look for a dark, usually white-bellied, gull-shaped bird that flies like it has three more high gears than the other seabirds. A typical strategy is for them to cruise low and slow just above the water’s surface until they spot a tern with a fish. When they’ve selected their victim, they shift into one of those higher gears and the chase begins. Terns are pretty good at flying themselves and initiate evasive maneuvers. From shore, you see the darker, bigger jaeger beak-to-tail with the tern, matching every high-speed zig and zag, often abruptly flying straight up. It’s an air show to make the Blue Angels blush with shame. The result is usually a dropped or disgorged fish, which the jaeger typically catches before it even hits the water. It’s breathtaking, really.
Any ocean beach with terns flying by is a good bet to see at least one mugging event right now through the end of next month, but you’ll need binoculars. Last week I watched a group of three, then four Parasitic Jaegers ganging up on terns as they worked their way north, first at Coast Guard Beach in Eastham and then at Nauset Light. The bay gets jaegers during and just after nor’easters, sometimes in numbers. They are less common away from Atlantic beaches, but look for them wherever terns are feeding in numbers. And as you just stand there and just watch the terns get robbed without intervening, just be glad that Massachusetts good Samaritan law from the last episode of Seinfeld is not a real thing, or you’d also be heading to jail.
