North Coast Diaries

The seawatcher's conundrum --- Saturday, August 15, 2009

"I never drive any faster than I can see" - Jack Burton

There has been some discussion about how confidently one can identify a bird that is way off at sea while standing on land. I have been watching seabirds from the South Jetty of the Columbia River for more than twenty years and have some sense of what is and is not possible. I own a 60mm Bushnell Spacemaster with a telephoto eyepiece. For general searching I set the eye piece at somewhere between 20 and 25.

I fully admit that I depend a great deal on general shape and impression when identifying birds at a distance. I take what I've learned from seeing a species at fairly close range and apply it to what I see at a distance. In other words, bird ID at a distance depends much more on experience, expectation and a best guess than birding up close and personal.

But what is reasonable when we report what we've seen or evaluated what others claim to see? To give folks a general idea of what's reasonable at a given distance I went out on the South Jetty with my 300mm telephoto and took some pictures at known distances. My camera does not have the resolution of a human eye (I can't afford that many megapixels) and a moving bird seen through a telescope contains more information than a static one frozen in time on a computer screen, but there are some things we can learn from the following experiment.

All of the photos presented below are from the same camera, set at the telephoto maximum for my camera. They have been cropped vertically, but all show the width of field maximum for the lens. They have been adjusted for contrast and sharpened.

A Common Murre at 50m

Surf Scoters at about 150m

The South Jetty viewing platform at 1.3km (0.8mi)

The end of the South Jetty at 3.5km (2.2mi)

The end of the North Jetty at 5.7km (3.6mi)

Tillamook Head and the Tillamook Head Lighthouse at 32km (20mi)

Obviously, this experiment would be even more meaningful if the photos had been taken through a spotting scope. The magnification and clarity of what I could see through both spotting scope and 8x42 binoculars was much better than what I could see through my camera view finder. But even in these poorly resolved photos, I can make out the pelicans at 2 miles...

Update: Here's a handy mariner's calculator for determining how far away the apparent horizon is from your selected "crow's nest". And for all the true math wonks, a discussion (with diagrams) detailing how these formulas are derived.

• Sunday, August 16, 2009 - Shearwaters on North Coast(Oregon) 8-15-09

Posted by Anonymous

We saw these birds just outside the breakers in low surf last evening at Sunset Beach, which is in between South Jetty and Tillamook Head. We watched them stream by for at least 45 minutes, scratching our heads and wondering what the heck these birds could be. They were still going strong when we left. There were also some pelicans and lots of terns and gulls right at the edge of the water. They eating very small fish, which were so close in we could see them from standing on the sand. This was one of the most amazing things I have ever seen.

When I went home and consulted my bird books some kind of shearwater was my first guess - I emailed my brother, who is more knowledgeable, and he sent me a link to your site. You and your friend's observations have made me confident that my hypothesis was correct. I had no idea that there were huge flocks of little birds that make a circuit around the Pacific Rim every year. I never would have thought that we would see birds here that nest in Australia, especially not hundreds of thousands of them all at once!

I agree that you have to go on what information you have -distance and lighting conditions on the water make it very difficult to see fine details. But the shape, movement, location, behavior, season, time of day, and in this case, the sheer numbers, can at least narrow down your list of suspects, and even obtain a conviction on occation.

I will add this site to my bookmarks - it's nice to know there is someplace to go on the internet with a focus here on the North Coast, so I can go home and say, "hey, I saw this," or "what the heck was that?" Thanks.

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• Sunday, August 16, 2009 - More re huge shearwater flock

Posted by Anonymous

I joined the Surfbirds site after posting the comment about the huge flock of Shearwaters at Sunset Beach. In reading posts in the forums and looking back at my books, I realize that the Sooties are 16-18". They were pretty close in and I don't think they were that big. Everyone was commenting about how small they were. I thought they looked like big chimney swifts, but not as big as a crow. They flew very close to the water's surface, sometimes dipping down into the water and back up as they flew. Wingbeats were rapid, like a duck.

My first take, not knowing anything, was the Short-tailed Shearwater, described as 13-14" in the Audubon guide, although Sibley says they are 16". According to Audubon, they also migrate in huge flocks and are summer visitors to the West Coast, although it states they are rare south of British Columbia. You obviously are much more experienced and knowledgable than I; I would appreciate your opinion on whether or not these might be one of the smaller shearwater species, rather than the Sooty.

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• Sunday, August 16, 2009 - Seaside Shearwaters

Posted by mbalame

The birds that have been massing off Seaside are Sooty Shearwaters. Size is a difficult thing to judge, especially in flying birds and most field guides make it seem like all the birds are exactly the same size and give the size of a dead bird lying on its back. Short-tails and Sooties are actually so close to the same size that you can't tell the difference accurately in the field.

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About these diaries:

Natural History along the Oregon North Coast, with side trips to other parts of the Pacific Northwest and the occasional digression into the philosophical esoterica of things sciencey...

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