Friday, February 28, 2014

Loose Feathers #433

Short-eared Owl at Lacreek NWR / Photo Credit: Tom Koerner/USFWS
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Friday, February 21, 2014

Loose Feathers #432

Northern Pintails in flight / Photo by J. Kelly (USFWS)
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Monday, February 17, 2014

Photos of the Week: Red-necked Grebe

Red-necked Grebe is the most difficult to find of the three grebes that regularly visit the eastern coast of North America. Pied-billed Grebes are fairly common on inland waterways, especially during their migration, and Horned Grebes are easy to find along the coast. Red-necked Grebes are another matter since most of them winter around the Great Lakes or Canada's Maritime provinces. To see one in the Mid-Atlantic, you either need to get lucky or know a location where one is reliable.

On Saturday, I got lucky and found one along the Raritan River at Edison Boat Basin. What started as a search for unusual gulls instead turned up an unusual grebe. It started snowing furiously around the same time I spotted the grebe, so the white specks in these photos are snowflakes. Red-necked Grebe is noticeably larger than the other common eastern grebes. It is easily recognizable among grebes because of its long, loon-like bill.

While this species is uncommon here, seeing one on Saturday was not entirely surprising. The persistent cold of this winter has frozen many waterways further north and is pushing many waterbirds south of their normal wintering grounds. This is especially true of Red-necked Grebes and White-winged Scoters, and there have been several reports of Red-necked Grebes around New Jersey in recent weeks. Perhaps I will find a White-winged Scoter soon too.

Friday, February 14, 2014

Loose Feathers #431

Sanderlings / Photo by Bill Buchanan (USFWS)
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Monday, February 10, 2014

The Aerodynamics of Diving Peregrines

Falcons are well known for their speed and agility. They prey primarily on other birds and generally catch their prey on the wing. (Small falcons like kestrels often eat large insects or small rodents in addition to birds.) All falcons are sleek with pointed wings and capable of fast flight, but Peregrine Falcons in particular are noted for their high-speed dives. I have been fortunate to witness such dives on several occasions, and they remain impressive every time. A recent paper in PLoS ONE examines the aerodynamics of diving Peregrine Falcons through a series of experiments.

A typical sequence of images taken during a dive at the selected points. Source: PLoS ONE
Peregrines were trained by falconers to dive in front of the south wall of a dam to allow high-speed cameras to capture their flight shape and trajectory precisely. The resulting photographs were then used to build a model for wind tunnel testing.

Flow visualization on the surface of the falcon model (A) and the falcon at the same flight position (B). Source: PLoS ONE
At the top of the dive, the falcon initially accelerated and then flew at constant speed with its wings tucked into a diamond shape. During this dive, the falcon reached a maximum speed of about 50 mph. As it approached its intended prey, it spread its wings to generate lift and rapidly decelerated, finally pulling out of its dive and landing. The wind tunnel tests showed several regions where the airflow was uneven around the model. At one such region, near where the trailing edge of the wing is tucked close to the body, photographs showed feathers popped up to smooth the airflow. Benjamin Ponitz, Anke Schmitz, Dominik Fischer, Horst Bleckmann, & Christoph Brücker (2014). Diving-Flight Aerodynamics of a Peregrine Falcon (Falco peregrinus) PLoS ONE DOI: 10.1371/journal.pone.0086506

Friday, February 07, 2014

Loose Feathers #430

Swans on Lake Mattamuskeet / Photo by Allie Stewart (USFWS)
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Wednesday, February 05, 2014

Review: The Warbler Guide

Warblers occupy a special place within the imaginations of North American birders. Warblers appear in a diverse array of colorful plumages, but they are not just eye candy. Their elusive habits and complex plumage makes finding and identifying them a satisfying challenge. Most birders have only a few weeks to see the vast majority of warblers in fall and spring, so there is little danger of their appeal wearing off, as sometimes happens with colorful resident species. Even after birding for ten years, I still have not mastered every plumage for every eastern warbler, and there are some species I still have not seen (like Kirtland's Warbler) or only seen once or twice (like Mourning and Connecticut Warblers).

Birders now have a new field guide to assist with finding and identifying warblers: The Warbler Guide by Tom Stephenson and Scott Whittle, published by Princeton University Press. The guide joins existing guides like A Field Guide to Warblers of North America by Jon Dunn and Kimball Garrett; Warblers of the Americas: An Identification Guide by Jon Curson, David Quinn, and David Beadle; and Stokes Field Guide to Warblers by Lillian Stokes.

A few features make The Warbler Guide distinctive. The most obvious at first glance is the sheer amount of visual information presented for each of the warbler species. (You can see a sample species account in this pdf.) For some species, the accounts are broken into drab birds vs. bright birds or fall vs. spring. To me, the accounts emphasize the best of the "field marks" vs. "whole bird" methods of identification. While it checks off diagnostic features (what might be called "field marks"), it goes beyond those to show how each bird appears from numerous angles. The photos also show characteristic behaviors and postures, which can be useful evidence in differentiating one species from another.

Another is that it uses a system of symbols and abbreviations with color coding to convey information about each bird. This may appeal some readers, but I prefer that a species account tell me the information in words rather than send me off to some key to find out what the symbol means. The guide also includes a quick finder that covers many angles and plumages. While useful, it starts on page 100, which makes referencing it less quick than it might be if it were placed near the beginning or end of the guide (as the quick finders are in the Crossley ID Guides). The publisher has helpfully provided PDFs of these quick finders on its website, for anyone to reference.

More important is the use of sonograms to represent warbler songs and calls. Sonograms were first introduced in printed field guides with Birds of North America: A Guide To Field Identification by Chandler Robbins, Bertel Bruun, Herbert Zim, and Arthur Singer, but they never caught on enough for authors and publishers of other birding field guides to feel the need to follow suit. Instead, it has been standard for field guide authors transcribe sounds into phonetic sounds, like kek-kek-kek-kek, or mnemonic phrases, like sweet-sweet-sweet-a-little-more-sweet. The trouble with the latter approach is that not everyone hears bird sounds the same way, and mnemonic phrases often do not the rhythm of the song they represent. Sonograms offer a more accurate way to represent bird sounds. However, sonograms take some skill and practice to interpret correctly. To that end, The Warbler Guide includes an extensive guide to sonograms and learning bird sounds in its introduction.

The Warbler Guide by Tom Stephenson and Scott Whittle is an innovative guide for learning and identifying North American wood warblers. It stands out from existing field guides, particularly in its inclusion of sonograms for every species. Any birder with an interest in warblers will want this guide as a stepping stone to more advanced identification skills.