Tuesday, April 04, 2006

Why Birds Sing Sweetly

A study of northern cardinals found that their songs sound sweet because they can modify their throats to control overtones. When we watch singing birds, we can see that their throats vibrate with each song. X-ray images reveal that the outward vibration is caused by the throat expanding and contracting with each note.

Overtones surround most sounds made in nature, including birdsong and human singing. Their volume relative to that of the fundamental pitch results in a sound that can be pure, rich, or muddled. Reducing the relative loudness of overtones will result in a purer sound.

Make sure to watch the include video clip, which shows the throat in action.

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Monday, April 03, 2006

Birds of the Mid-Atlantic #5: Red-shouldered Hawk

The red-shouldered hawk is a characteristic raptor of eastern woodlands. They get their name from the rufous coloration on the leading edge of their wings, which are otherwise checkered with black and white. The scientific name, Buteo lineatus, refers to the black and white striping on its tail.

Red-shouldered Hawk / Photo by Lee Karney (USFWS)

The harsh, insistently-repeated territorial calls of red-shouldered hawks are easily recognizable. Listen to a sample here. Be careful, though, not to be tricked by a blue jay. Blue jays frequently mimic the calls of red-shouldered and other hawks. In breeding season such mimicry may cause other songbirds to vacate their nests, leaving the eggs open to predation by blue jays.

Unlike red-tailed hawks, which seem able to thrive in any habitat, red-shouldered hawks have a strong preference for mature woodland near streams and wetlands. Their diet is heavy in reptiles and amphibians, characteristic wetland animals, though they will also take small mammals.

The population of red-shouldered hawks has declined considerably over the past century, due to pesticides and habitat loss. While numbers have improved somewhat since the banning of DDT, the loss and degradation of habitat continues to be a threat.

You can see more pictures of this beautiful hawk at the Canadian Peregrine Foundation.

Cross-posted at Blue Ridge Gazette.

Loose Feathers #37

News and links about birds, birding, and the environment.

  • Good news for red knots: New Jersey's Marine Fisheries Council voted to approve a two-year moratorium on collecting horseshoe crabs, which will allow time for the crab population to rebound and perhaps for the red knot population to stabilize.
  • In New York City, WBAI-FM's Eco-Logic show will be doing a spot on birds and birding on Tuesday, April 4, at 11 am. The station's call number is 99.5 FM and a podcast will be available from their archive page. Brooklyn bird blogger City Birder is slated as a guest.
  • Here is a website on Gull Identification. It takes a useful approach to a difficult group of birds.
  • A Stanford report finds that a majority of Americans think that the natural world will be in worse shape ten years from now. 86% want significant action from the government to correct the problems. 69% believe in global warming. This could be a potent issue for candidates inclined to use it.
Koufax Awards
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Sunday, April 02, 2006

Kenilworth Birds

Despite the especially lovely day, I spent most of the day inside for a DC Audubon organizational meeting. Luckily for me, and the rest of us, the meeting was at Kenilworth Aquatic Gardens. DC Audubon has had a special relationship with this park for a long time and runs an annual field trip in the gardens. So there was a short opportunity for birdwatching built into the schedule.

I saw my life broad-winged hawk this morning, thanks to one member who pointed it out to the group. Now that I have seen one, I think that the main thing holding me back from recognizing one previously was that I was probably misidentifying juvenile broad-wingeds with very light red-tailed hawks. That may explain why I had not seen this rather common migrant.

The river trail held a collection of woodpeckers and sparrows, plus a lone osprey dining on a fish. The marsh held several sandpiper species: greater and lesser yellowlegs and Wilson's snipe. The snipe in particular gave great looks, as they were sitting out in the open on a mud flat. In addition there was a group of green-winged teal swimming near the Anacostia inlet. Wood ducks were flying back and forth from one area of the gardens to another.

Marsh grasses sprouting on the banks of a lily pond

SPECIES SEEN: 39

Double-crested Cormorant
Great Blue Heron
Canada Goose
Wood Duck
Green-winged Teal
Mallard
Osprey
Red-shouldered Hawk
Broad-winged Hawk
Wilson's Snipe
Greater Yellowlegs
Lesser Yellowlegs
Ring-billed Gull
Rock Pigeon
Red-bellied Woodpecker
Downy Woodpecker
Northern Flicker
Eastern Phoebe
Tree Swallow
Ruby-crowned Kinglet
Cedar Waxwing
Gray Catbird
Northern Mockingbird
Brown Thrasher
American Robin
Carolina Chickadee
Tufted Titmouse
Blue Jay
American Crow
Fish Crow
European Starling
Yellow-rumped Warbler
Song Sparrow
Swamp Sparrow
White-throated Sparrow
Dark-eyed Junco
Northern Cardinal
Red-winged Blackbird
Common Grackle

Trilling Birds

For yesterday's walk I chose the National Arboretum. On a day when lots of people were sure to be out, it allows plenty of room for people to spread out and not crowd each other. I did not see any new birds for the year. The same species that persisted through most of March were there yesterday, with a mix of lingering winter birds and a arriving spring birds. Flocks of white-throated sparrows and dark-eyed juncos seem to be considerably smaller now than a few weeks back. The largest single flock I saw yesterday was probably the sixty or so cedar waxwings all calling from a tree in the Asian garden.

I had a lesson in one of the more difficult song groups yesterday afternoon. Trills (in birdsong) consist of a single pitch repeated rapidly. Chipping sparrows have a fast dry trill. I heard one of these singing in the field across from the azalea gardens. Pine warblers have a softer slower trill, one with a clearer tone. I heard this song in the state tree grove, and had a chance to watch the warbler lean its head back to sing. A third species known for its trilling song, the dark-eyed junco, was present, but I did not hear it singing.

Butterflies abounded in the sunnier areas. I saw my first-of-the-year spring azures, as well as my first variegated fritillary. I made several attempts to photograph the latter. After several fruitless attempts, I finally caught it in the photograph at the bottom of the page. I hope to take better butterfly pictures than this as the year progresses.

Finally, yesterday was a very changeable day. One moment it would be sunny, and another the sky would cloud over as if it were about to rain. Fortunately it did not rain while I was out walking. I tried to capture this feeling with the (heavily edited) photograph below.


BIRD SPECIES SEEN: 31

Double-crested Cormorant
Canada Goose
Ring-billed Gull
Rock Pigeon
Mourning Dove
Red-bellied Woodpecker
Northern Flicker
Pileated Woodpecker
Eastern Phoebe
Golden-crowned Kinglet
Cedar Waxwing
Carolina Wren
Winter Wren
Brown Thrasher
Eastern Bluebird
Hermit Thrush
American Robin
Carolina Chickadee
White-breasted Nuthatch
Blue Jay
American Crow
Fish Crow
European Starling
Pine Warbler
Eastern Towhee
Chipping Sparrow
Song Sparrow
White-throated Sparrow
Dark-eyed Junco
Northern Cardinal
Common Grackle

BUTTERFLY SPECIES SEEN: 4

Cabbage White
Clouded Sulphur
Spring Azure
Variegated Fritillary