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Posts Tagged ‘Tracking’

You’ve seen them on docks. You’ve seen them on dumpsters. They eat fish, french fries, and everything in between. But where do all these gulls come from? And where do they go once they’ve finished their lunch?

 Gulls can be found just about everywhere there’s water (and plenty of places where there isn’t). There are plenty of them around, and they’ve gained a reputation as garbage-eating pests.  But there’s way more to a gull than dumpster diving.

Some gulls, like this Great Black-backed Gull, are actually quite handsome! - Photo by Zak

Some gulls, like this Great Black-backed Gull, are actually quite handsome! – Photo by Zak

First of all, gulls are actually cousins of the terns we’re working so hard to protect out on these islands, and these cousins have a lot in common. Both terns and gulls prefer to nest in large colonies, and lay their eggs in nests on the ground. They’re both strong fliers, capable of traveling long distances over the ocean (although nothing quite tops the pole-to-pole migration of the Arctic Tern).  Males and females of both tern and gull species are almost identical (although males tend to be a little bigger) and both parents work together to raise their chicks.

So why have gulls done so well when terns are in trouble? It all comes down to food. Gulls are opportunistic – they’ll eat anything. Terns are picky eaters – they generally only eat fresh-caught food they pluck from the water themselves. Like a tern, gulls also love fish. But they’ll also eat mussels, urchins, crabs, and in recent years, human refuse. They’ve learned to follow fishing boats, flock to open dumpsters, or sometimes snatch food right out of people’s hands. So gulls have thrived on these new abundant food sources, while terns have been struggling.

A Herring Gull, Metinic's most common gull - Photo by Zak

A Herring Gull, Metinic’s most common gull – Photo by Zak

But we and the Refuge have been wondering, where exactly do Refuge Island gulls get their food? Does a gull here on Metinic fly all the way to the mainland for a meal? Or do they stay local and snack in the intertidal zone? This year is the pilot year of a study to answer those very questions with the help of GPS.

So, what’s the plan?

Step 1: Catch a gull.

The best way to do this is on the nest. The setup is simple enough: the gull sits on a string tied to a wooden prop. The prop separates into two pieces and the box falls down, capturing the gull. We replace the real eggs with wooden ones so they won’t accidentally get crushed. Sounds easy enough, right? Maybe not.

Some people call gulls rats with wings – and it’s not a total misnomer. Both rats and gulls are a lot smarter than many people think.  It took us several hours of trapping to catch our first Herring Gull.

Catch me if you can!

Catch me if you can! AKA, Gulls – 3, Biologist-0

Step 2: Attach a GPS Logger

These little boxes, called igotU tags, are programmed to take a GPS reading every 3 minutes for about 4 days. To attach one to a gull, we put it in a waterproof casing then tape it to the gull’s back feathers with extra strong tape. The tag is light enough that it won’t hinder the gull when it flies, and hopefully the tape will keep the gulls from preening the tag off.

igotU tag getting taped to a Herring Gull's back - Photo by Amy

igotU tag getting taped to a Herring Gull’s back – Photo by Amy

We also band the gull and take a few measurements to determine if it’s a male or female.

Zak checks a GPS tag

Zak checks a GPS tag on a Herring Gull

Step 3: Release the gull!

Amy releasing a tagged and banded Herring Gull - photo by Zak

Amy releasing a tagged and banded Herring Gull – photo by Zak

Step 4: Trap the gull again.

To get the data from the GPS loggers, we have to trap the gull again and remove the tag. Stay tuned for Part 2 to see what we find out!

IMG_1386 (640x427)

A GPS-tagged Herring Gull on its way – Photo by Zak

– Amy

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