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Posts Tagged ‘Geolocator’

It’s been a beautiful week on Metinic, with the warm sun providing for excellent hatching weather. More tern chicks show up every day in our plots and some of the older ones are getting their first wing feathers. Of the dozens of chicks in our plots, the color and pattern can vary considerably from sandy tan chicks with only a few black spots to almost snowy white speckled with dark streaks.

silver_gold siblings

We call these arctic tern chicks the “Silver and Gold Siblings”

We made the most of the weather early in the week to continue our trapping efforts, with a special focus on one particular bird. In 2010, Refuge staff placed geolocator data loggers on the legs of several arctic terns to track their annual journey from breeding grounds in Maine to their winter range in the waters around Antarctica. The geolocator measures the amount and timing of sunlight to determine the location of the bird. Most of the loggers were retrieved in 2011 or 2012, but a few were still missing. Luckily, Helen and I spotted this bird in May, and figured that it was breeding here. On Wednesday, Refuge staff Brian, Michael, Linda, and Sara came out to the island to locate and catch the bird. Between the six of us, we sat in our five blinds and watched for the bird. We quickly found the bird and its nest, but trapping efforts were to no avail. After a fruitless attempt on Thursday, Brian and Michael came back out on Friday and finally managed to catch the bird after a few hours of waiting with a bow net. It appears that the nest is being attended by three adult terns, which is unusual, but may account for the difficulty of catching the bird if it’s only spending a third of the time on the nest. The geolocator was removed and the bird released. Hopefully, the data on the geolocator can be retrieved and we can see where the bird has been!

geolocator

The geolocator on the tern’s leg before it was removed

While the Friday tern trapping stint was ongoing, Helen and I went out to check on black guillemot burrows on the northwest side of the island in advance of hatching. June 27th is International Guillemot Appreciation Day, traditionally around when the first chick hatches. Guillemots, relatives of puffins, nest in rock crevices all along the Maine coast. We located several rocky burrows with eggs and a few with adults attending. Between the burrows, a few gull chicks were running around near their nests atop the rocks.

blgu on nest

An adult black guillemot incubates its eggs in a rock crevice

gull chick

Herring gull chick. Both herring and great black-backed gulls breed on Metinic.

At the southern end of the cliffs, we were checking a last couple of rocks when we were surprised to find our first guillemot chicks a few days early!

BLGU chicks

Black guillemot chicks are covered in dark gray downy feathers

Have a happy Guillemot Day!

-Mark

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Arctic Terns have arguably the most impressive migration of any bird – they travel from the Arctic to the Antarctic and back again just about every year of their lives.  While we’ve known for a while where the terns travel, how they get there has been something of a mystery. Do they travel along the coastline? Do they take a direct route from Maine to the Antarctic coast? Do they do a marathon flight from pole to pole, or make pit stops along the way?  These questions were nearly impossible to answer until very recently, for the simple reason that following a single tern (or even a flock of them) is nearly impossible. Terns are small birds – a little over 100 grams, or 3.5 ounces – so they can’t be equipped with heavy satellite tags. They also do mostof their traveling over water, so the odds of spotting a tern on its migration are slim.

Enter the light-level geolocator, here to solve these problems and answer many of our migration questions

A geolocator, wrapped in a waterproof cover, attached to the leg of an Arctic Tern

A geolocator, wrapped in a waterproof cover, attached to the leg of an Arctic Tern

Four years ago, in the summer of 2010, the Refuge deployed 30 geolocator tags on 30 separate Arctic Terns. These tiny tags are lightweight enough that they don’t hinder the terns as they travel (in fact, they’ve been used on even smaller birds, like Purple Martins). They work by using detecting light levels and recording the time of sunrise and sunset every day. Since the length of day and the time of sunrise and sunset are slightly different at every point on the globe, this information can be converted into a rough map of everywhere the tag, and by extension the tern, has been.

A pretty miraculous little gadget, isn’t it? But there’s a catch: to reduce weight, the geolocators don’t transmit the data they gather, they simply record it. To get at all that information, the tag must be retrieved and physically attached to a computer. This means the tagged birds must be recaptured and the tags removed before they do us any good.

A geolocator (right) and a field-readable band (left)

A geolocator (right) and a field-readable band (left)

Recapturing a bird can be difficult. The best way to do so is to find the bird’s nest, and use a trap that springs while the bird is incubating. That, however, requires the bird to be able to find a mate. Last year on Metinic, Zak and I spotted a geolocator-equipped tern who had eluded capture for 3 years, but we couldn’t get our hands on him because he didn’t have a mate or a nest.  He spent all summer trying to court various female terns with fish, but there were no takers.

Hard to believe such a good-looking guy couldn't find himself a date

Hard to believe such a good-looking guy couldn’t find himself a date

This year, our lonely tern returned and found himself a mate. Syd and I set up a trap called a bow net trap, which is triggered by the tern attempting to incubate a set of fake wooden eggs (the real ones are safely stored in a blind so they aren’t crushed by a struggling tern). It took a couple of tries, but today we succeeded in capturing the handsome gentleman we have nicknamed Giovanni (Geo, for short).

Syd and Geo

Syd and Geo

Geo was released back to his mate and eggs, probably glad to be rid of his extra baggage. The geolocator will be returned to Refuge staff, who will hopefully be able to use it create a roadmap of Geo’s travels from the past four years. That could be up to eight traps between Maine and Antarctica – more than 70,000 miles!

Geo, free of the geolocator and sporting a shiny new band

Geo, free of the geolocator and sporting a shiny new band

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For how much information they can hold, the geolocators are very small!

As the Terns get ready to migrate south at the end of the season, it makes you wonder “where are they going?”  Last year on Metinic Island, refuge staff attached geolocators onto Arctic Terns in an effort to find out just that!  These particular geolocators work in an incredible way.  GPS or satellite tracking equipment is expensive and heavy.  These lightweight little units monitor time of sunrise and sunset instead, and from that data can give an approximate location on the globe.

This little device has tracked an almost 40,000 km round trip migration, we cant wait to see the map!

This year after a tremendous amount of searching, locating, and trapping, we were able to recover a few of the geolocators and are waiting to receive the data back from them.  Soon we will have a map of the flight paths of a few Terns nesting on Metinic, and we will know not only where they went after last year, but how they got there!

-The Metinic Crew

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