Arctic Tern - A Life of Ice, Light and Flight

On the afternoon of January 12, 2015 I was immersed in a surreal setting of ice, snow and water. We were just west of Booth Island and north of Pleneau Island on the Graham Coast of the Antarctic Peninsula. Above me in the clouds to the east were Mt Shackleton and Mt. Scott, but I had to trust the map to tell me that. There were no mountains to be seen that day. The clouds were low and large flakes of snow floated from the what was left of the sky, seemingly spontaneously forming just above our heads.

We were there because of the icebergs. This area is a frequent stop of tour ships because the currents and islands conspire to push icebergs into this area where they slowly decay into constantly changing abstract sculptures.
The day had started out with a curious Minke Whale checking out our Zodiacs as the staff prepared to transport guests to Peterman Island where we were able to visit colonies of breeding Gentoo and Adelie Penguins with a few Blue-eyed Shag nests in the mix.

Sandra and her friend the curious Minke Whale.

The afternoon was spent in the zodiacs, maneuvering through the shifting mountain ranges of icebergs, brash ice, and bergy bits to fully experience a true Antarctic spectacle of ice.

A chunk of bar ice where you can see how the water erodes small cup shaped divots from the ice. Photo by Sandra Petrowitz.

Perhaps just as interesting for me were a number of birds we found perched on the icebergs and feeding in their shallow pools. They were Arctic Terns and there were more of them in one spot than I have ever found on the Antarctic Peninsula. 

They were perched high on the ramparts of towering bergs in an Antarctic version of birds on a wire. 

The migration of this species is quite remarkable. They breed in their namesake region - the Arctic, but then migrate south through the Atlantic Ocean (and probably the Pacific Ocean as well) to spend their non-breeding summer in the Antarctic Pack ice. We know more about the portion of the population the migrates through the Atlantic through some interesting research conducted on Arctic Terns in Greenland and Iceland known as the Arctic Tern Migration Project. Below are a couple of maps that show the migration route and winter areas of the eleven birds they tracked (both images from the Greenland Institute of Natural Resources)

Simplified figure showing migration patterns of the Arctic tern, from the breeding sites in Greenland and Iceland to the winter grounds at Antarctica. After initiating the southbound migration (yellow line) the birds paused their migration in the central part of the North Atlantic (small circle) for almost a month before they continue towards the wintering sites at Antarctica (large circle). In spring, the northbound migration (white line) is conducted more than twice as fast in a gigantic “S” shaped pattern through the Atlantic Ocean. Areas particular rich in biological productivity are indicated by yellow and green colors.

Interpolated geolocation tracks of 11 Arctic terns tracked from breeding colonies in Greenland (n = 10 birds) and Iceland (n = 1 bird). Green = autumn (postbreeding) migration (August–November), red = winter range (December–March), and yellow = spring (return) migration (April–May). Two southbound migration routes were adopted in the South Atlantic, either (A) West African coast (n = 7 birds) or (B) Brazilian coast. Dotted lines link locations during the equinoxes.

As you can see from the map above, the wintering area for most of these birds is the edge of the pack ice in the northern part of the Weddell Sea. Presumably they spend their non-breeding summer much like I observed them - foraging among the ice in the open waters between the ice as well as the shallow waters formed by the icebergs themselves.

One iceberg in particular formed a spectacular eroded backstop for the foraging terns. 

There were a few other creatures foraging in the same area with the terns. We observed another less inquisitive Minke Whale that afternoon as well as a Crabeater Seal lounging in an iceberg pool and a few Kelp Gulls. 

So why did I see so many on this trip? One explanation is that I just hadn't been in the right place at the right time and they have always wintered in this area. However, I believe that this year the pack ice was so heavy in the Weddell Sea that there was essentially no open water and the birds wound up concentrating along the Antarctic Peninsula in numbers that would not be found during a "normal" year just to be able to find something to eat. 

Perhaps a more fitting name for this bird would be the Polar Tern, since they spend a majority of their life in both polar areas where they also experience perpetual daylight. The distances these birds migrate is impressive and when they are not breeding or wintering in the polar regions they are flying in a twisted migration loop back and forth across the Atlantic Ocean. 

The Story of Pronghorn 166

Last year about this time I witnessed the capture of a Pronghorn doe. She was spending the winter just west of Glasgow with a large group of other Pronghorn. She was singled out and captured by a crew using a helicopter and a net gun and then fitted with a GPS collar as part of a research project by Andrew Jakes. The number written on her ear tag is 166. I have previously posted about her capture and location over the summer.



A few weeks ago I received a phone call from Andrew. He had just completed a flight to see if the animals wearing collars for his study were still alive after this extraordinarily snowy winter that has been so hard on these animals. Surprisingly, most of his animals were still alive, but he informed me that 166's collar was emitting a mortality signal (if the collar does not move a certain period of time, the signal changes so that researchers know the animal is most likely dead).



The news wasn't entirely unexpected with the number of animals dying this winter. However, what he told me next was rather remarkable.
Andrew told me they thought she was next to the highway and that she had probably been struck by a vehicle.





That wasn't the remarkable part; lots of Pronghorn have been struck and killed by vehicles this year.
The remarkable part was where it happened.
The mortality signal from her collar told us she was about 9 miles west of Jordan, Montana near highway 200. This location is approximately 70 miles south of where she was captured last winter and in between was Fort Peck Lake and miles of rugged Missouri River Breaks habitat not generally known as winter habitat for Pronghorn.
I had just driven that highway a day earlier and went right past her. My path and hers had crossed again, although at the time I didn't know it. I had noted a number of dead antelope on that trip and I even thought I might know exactly where she was at.



Ten days ago Kelvin Johnson, FWP biologist from Glasgow, and I headed south to find her. We found plenty of Pronghorn on our drive south, all gathered together trying to make it through the winter.

The animal I remembered in the ditch was a buck and about four miles for the spot we were given. About a half mile from the location, we found the remains of about four road killed Pronghorn and figured she must be in this group. The receiver picked up no signals and none of the heads we could find had an eartag. We continued down the road to our given location and found a lot of Pronghorn wintering just south of the highway. But we didn't find 166. No signal. Nothing.



This is the area we were searching in.



We walked around a bit and went to the top of the ridge near the location, and turned the antenna in all directions, but still no signal. We headed home disappointed to not have found her and speculated a number of different ways to explain why we couldn't find her. My sentimental favorite was that she had just stayed curled up for so long that the mortality signal had kicked on but she was still alive and now was wandering around further south. There were two other live Pronghorn with collars in the area (both had made a similar trip as 166), but we didn't pick up the signal from those animals either. Maybe the receiver wasn't working well. Maybe.....

Another flight early last week put to rest my idea that she was still alive. The location of the mortality signal was a bit elusive, but it was still there. A new location, not that far from the old location, was passed my way.

Last Friday I was once again heading down this highway on my way home. I really wanted to be the one to find 166. She had become a special animal to me so I borrowed an antenna from the FWP biologist in Billings and a receiver from another FWP biologist in Roundup and headed north. I had gotten out of town much later than I had wanted and it was starting to get dark when I got near the new location. I knew that the signal on the collar quit for portions of the day but I didn't know when that was. I told myself that if I put the antenna on the receiver and wasn't able to pick up a signal, I would have to try again another day. It was quite cold and blowing when I stepped out of the car and turned on the receiver. I tuned in the frequency, plugged in the antenna and immediately heard loud beeps coming from here collar. I was very close.



The signal directly led me down the ditch on the north side of the highway about a quarter mile when I noticed a leg sticking out of a snow bank and then the top of a Pronghorn head. I pulled the antenna off the receiver and waved the receiver over the head. No signal. Must not be her but I know she is close. As soon as I put the antenna back on the receiver it became very apparent that the antelope I was looking at had to be her. I brushed the snow back from around her neck and there was the collar. I had found her. It was close too - I later found out the transmitter was scheduled to turn off at 5:00 pm and the time on my photos was 4:46.



Above you can see the back of her head with the yellow ear tag. There was a small chunk of wire stuck in the eartag - a testament to the trials these animals undergo each year during their migrations. The prior week she must have been too well buried in the snow for us to pick up a signal from her collar.



Above is a GoogleEarth map where I plotted the known locations we have of 166 from the VHF transmitter on her collar - where she was captured (in the middle), her summer location (top, just north of Limerick, SK), and her final location (bottom) - a line nearly 170 miles long. It was amazing how near her capture location was to a straight line between her summer spot and the point of her demise. But the more interesting part is going to be when we get the GPS locations from her collar to see what she did in between those points and the path she took to get that far south after the snow started. So - more to come regarding the story of Pronghorn 166 and her extraordinary journey.

Odds and Ends

So many posts have come and gone through my mind over the last few weeks but never made it here for one reason or another.

There was the day the crows were migrating through in long scattered groups. The sight reminded me of the fall day a number of years ago when I was watched a long broken line of these birds chasing the light south. At the top of a large hill near here, I was able to connect scattered groups of crows from as far as I could see to the north, over my head and again as far as I could see to the south - with my spotting scope! This stringy line of scattered crows, moving near the earth stretched for at least 10 miles. Maybe they really stretched from daylight to dusk.




Then there was the first flock of cranes. Sandhill cranes in swirling lines forming large masses moving in the same direction as the crows, but much higher. The fall cranes always prompt memories from my childhood of walking home from school for lunch on a yellow October day and hearing that sound. If you have heard it before you know what I mean - that rolling call of the Arctic and muskeg connecting to the playas of the southern grasslands. I remember being stopped in the open field between the school and my house when the churling bugles registered in my mine and my eyes moved skyward to trace the sound to the gathered specks moving south in shifting lines high above me.





Oh, and ambiguity and bird identification from David Sibley mixed with the Dunning-Kruger effect (from a post by Pluvialis at Fretmarks) prompted lots of thoughts, particularly during this time of year when I am reviewing a number of bird observations submitted to the Montana Bird Records Committee for review. But I am not going to chase that right now.


Then there are these guys...





And her..





And it is a gorgeous fall day in October, upland gamebird season is on, waterfowl opened last weekend, birds are migrating through, I can see the bison grazing out my front window as I type this and I should not be sitting in front of my computer. My camera/binoculars/shotgun should be in my hand and I should be out the door and.....did you hear the door slam shut behind me?

"Eastern" Montana Birds

Yellow Warbler


During spring migration this year my friend Steve Bodio commented on the number of "eastern" birds we were finding in this corner of Montana. I promised I would return to the subject in a future post. I figured it was finally time for the post on Steve's comment now that those same birds are moving back through our area in the other direction!

Yellow Warbler


The species Steve mentioned were the Rose-breasted Grosbeak and Broad-winged Hawk but there are many more "eastern" species that move through here. To illustrate this discussion I would like to first mention Westby, MT, a small town as far northeast as you can get in MT without venturing into Canada or North Dakota. My friend Ted Nordhagen has lived and birded here since he was little and it has become a hotspot for Montana birders. Here is a list of species found in Westby this fall (spring is similar):

Ruby-throated Hummingbird
Alder Flycatcher
Least Flycatcher
Olive-sided Flycatcher
Red-eyed Vireo
Warbling Vireo
Blue-headed Vireo
Philadelphia Vireo
Swainson's Thrush
Tennessee Warbler
Chestnut-sided Warbler
Black and White Warbler
Blackburnian Warbler
Bay-breasted Warbler
Blackpoll Warbler
Yellow Warbler
Mourning Warbler
Canada Warbler
Orange-crowned Warbler
Yellow Warbler
Cape May Warbler
Yellow-rumped Warbler
Black-throated Green Warbler
American Redstart
Ovenbird
Northern Waterthrush
Wilson's Warbler
Rose-breasted Grosbeak
Baltimore Oriole
White-throated Sparrow
Lincoln's Sparrow
Purple Martin
Purple Finch

Common Yellowthroat



Many of the birds on this list may seem like "eastern" birds to us living in the United States but in reality they are boreal birds that breed as far west as Alaska (see figure 1 below).

Figure 1. Boreal Forests of North America (found here)

The reason we consider them eastern birds is because most of these species migrate through the eastern portion of the United States to reach the boreal forests, even the forests in Alaska.
So why are these birds being observed in Montana?
There are known migration routes in North America known as flyways. These are pathways that many birds migrate along when returning from or heading to their breeding areas in North America. Figure 2 below illustrates those routes.

Figure 2. Flyway routes in North America (from here).

In particular, I would like to discuss the Mississippi and Central Flyways. The maps below illustrate each of these flyways individually.

Figure 3. Central Flyway (from here)

Figure 4. Mississippi Flyway (from here).

Notice that the eastern portion of the Mississippi Flyway just cuts across the extreme northeastern corner of Montana. The main portion of the Central Flyway also comes through far eastern Montana. The boreal breeding birds that migrate up the Mississippi Flyway cut across northeastern Montana on their way to and from the far western reaches of the North American boreal forests. These are the same birds that migrate across the Gulf of Mexico to and from South America. Westby, Montana is right in the path of this river of birds and Fort Peck, just 125 miles to the southwest, lies in the backwater eddies of the river. We still find many of these species, but no where as regular or in the numbers found in Westby. Although this line appears to be curved in reality it is nearly a straight line between the northern part of the Yucatan Peninsula and the western reach of the boreal forest in Alaska (Figure 5).
There are still a few boreal species that we do not find in either place with as much regularity as their breeding distribution would suggest. These include the Swamp Sparrow, Connecticut Warbler, Eastern Phoebe, and Great Crested Flycatcher.

Figure 5. Straight line between the Yucatan Peninsula and the boreal forests of Alaska.

A side note on bird migration in Montana concerns the Pacific Flyway (figure 6). Note the branch of this route that comes into Western Montana along the Rocky Mountain Front. The birds utilizing this route, most notably the Snow Goose, winter in the Central Valley of California and cross the Great Basin in Nevada to continue north over the mountain of southwestern Montana and then along the Rocky Mountain front through Canada and into central Alaska. This route is repeated in the fall when these birds return south. One of the primary stopping points for the Snow Geese is Freezout Lake near Choteau, Montana where thousands of birds can be found during migration.

Figure 6. Pacific Flyway (found here)