I had a very sick Common Redpoll at one of our feeders this morning, a situation being reported elsewhere as well. Cause is believed to be dirty feeders. Our damp, cold spring is part of the problem. Wet seed debris in feeder trays and spoiled seed provide places for growth of what is believed to be salmonella. Our bird sat quietly, feathers fluffed up, head tucked to the side. It allowed me to approach far closer than normal before it weakly flew into the brush. Our worst problem is with thistle seed. Much of it gets tossed into the tray by feeding birds. A little moisture and you have seed paste. I cleaned feeders last week, but the problem can return quickly. It’s a good idea to clean all of your feeders now even if you see no sick birds. Empty the feeders, soak and scrub them in soapy water. Disinfect them with a 10 percent bleach solution. Let them dry thoroughly before adding fresh seed and putting them back out. I’m going to clean ours again, and I’m taking the thistle feeder down until the redpolls and siskins move north into their summer territories. Oh: seed debris on the ground also can be a problem. I use a shop vac to remove it. The National Wildlife Health Center Web site has more information. Go to www.nwhc.usgs.gov

Resident bird species are just getting into courtship, most migrants are yet to arrive, but Great Horned Owls have chicks in their nests. These young birds are perhaps two weeks from fledging — leaving the nest to begin their training for self-sufficiency. It will last into fall. Crowded into this nest, found in Burnsville yesterday, are one adult owl and two chicks. When it comes to being babies and cute, mammals have a real edge over birds.

Chickadees are among those bird species that nest in cavities. Unlike woodpeckers, they are not equipped to chisel a hole. However, they can pick away at dead wood to open a hollow for their nest. The chickadee shown here was working on soft wood atop an apple tree stump early this morning. Two birds, the male and female I presume, were taking turns chipping small chunks of wood loose, and tossing them away. The nest will be exposed to weather, but the sitting bird will shelter the eggs and young.    Â

A reader sent me this photo recently, asking, What is it? It’s a Domestic Mallard, sometimes all white with yellow-orange bill and legs. It’s also known as a Peking Duck. People raise them. Sometimes you’re seeing their livestock, sometimes an escaped bird. Interbreeding with wild ducks can cause puzzling plumages.

I’ve mentioned this before: the Web site of grrlscientist is worth a regular visit. Devorah Bennu, of Brooklyn, N.Y., offers a consistently interesting collection of photos and text about birds. The address is http://scienceblogs.com/grrlscientist/. This week, check out the Spoon-billed Sandpiper, and read the article about Gouldian Finches and how the females of that bird species can determine the sex of their offspring. She posts new material each week. Her Web address is listed at the right on this page. On the Web site of the National Wildlife Refuge Association (www.refugenet.org/birding/birding5.html) you can find an archive of its regular Birding Community E-bulletin, also consistently interesting and worth a look.

Perhaps you remember the story in the Home and Garden section last spring about a Pileated Woodpecker that chose a Wayzata power pole as its nest site. It dug one hole. The power company put a patch on it. It dug a second hole. The power company wrapped that section of the pole with wire mesh. That was that for the 2008 season. The bird has returned for another try, chiseling away Monday afternoon on a handsome nesting cavity about two feet above the wrap. Stay tuned.

Northern Flickers come in two flavors — yellow-shafted and red-shafted. The latter most often are seen west of the Great Plains. Here, we would expect to see yellow-shafted birds, like the one shown in the first two photos. It was in our backyard a couple of days ago, taking advantage of sunshine to do some grooming. The wing-feather shafts are yellow, as are the interior feathers of the wing. Tail feather shafts and the underside of the tail feathers also show yellow. You can see that in the photo taken last spring of three flickers engaged in some courtship action. The black mustache mark indicates a male bird.

 All it took was that one warm day a couple of Saturday’s ago when the temp rose above 40 to produce spring bird song. The chickadees in our neighborhood suddenly began to sing their loud fee-bee song. This can be heard throughout the year, but is more common in spring and summer. It’s sung by males to advertise territories and repel rivals. One warm day and they were thinking of girls. Cardinals here also began to tee up on tree tops and sing their availability advertisement. Yesterday’s snow did nothing to slow them up. The trigger is the increasing amount of daylight we’re receiving. In the photo is a male cardinal.

 Boreal Chickadee is one of the bird species tracked in the recent study by National Audubon of climate-change impact on winter range. Minnesota has lost over 90 percent of its wintering Boreal Chickadees to northward movement, according to the study. Audubon used Christmas Bird Count data from the past 40 years from both the U.S. and Canada. It determined a line at which an equal number of birds of a particular species was reported on each side, north and south. In 1968, that line for Boreal Chickadees was almost 300 miles south of where it is now. When Bob Janssen published his 1987 book “Birds in Minnesota” he wrote that migrant Boreal Chickadees were reported “every fall” in Duluth. In addition to counting raptors, observers at Hawk Ridge in Duluth have for the past two years counted migrants of all species. Six Boreal Chickadees were seen in 2007, none in 2008, according to Debbie Waters, education director for the Hawk Ridge Bird Observatory. The habitat conditions this little bird needs are changing. Today, it can survive the weather found north of their former winter range. Other bird species reported in declining numbers here are American Three-toed Woodpecker and Bohemian Waxwing. On the other hand, 18 species are more common here in the winter than they were in 1968. They are Rough-legged Hawk, Dark-eyed Junco, Hermit Thrush, Purple Finch, Northern Harrier, Sharp-shinned Hawk, American Crow, Green-winged Teal, Ring-necked Duck, Tundra Swan, Cedar Waxwing, White-throated Sparrow, Redhead, Mourning Dove, Red-breasted Merganser, Caroline Wren, Gadwall, and American Robin. Some of these birds are staying the winter. Others are able to linger longer before moving south (if they do) because, apparently, milder weather allows them to do so. Robins are an obvious example of increased winter population: thousands of robins have been observed in Minnesota this winter, and they’re doing just fine, thank you. (The Boreal Chickadee in the photo was found last week nibbling deer parts along Admiral Road in the Sax-Zim bog area northwest of Duluth.)

 White-winged Crossbills, a finch species of northern spruce forests, are being seen in many areas of Minnesota this winter, including the Twin Cities. Crossbills feed on the seeds found in spruce cones. The cone crop in Canada is poor this winter, so the birds have moved south in search of food. They’ve been seen in Minneapolis, Plymouth, Falcon Heights, Mendota Heights, Hastings, and Sherburne County, among other metro locations, and from Ely and Hibbing south to Fillmore and Houston counties. They’re being reported from all over. Any spruce tree with cones is a candidate for crossbills. The birds do indeed have mandibles that cross, allowing them to pry cone sections open so they can extract the seeds. These birds were photographed at the parking lot of the TwinWest Chamber of Commerce in Plymouth. The bird above is a female,  below a male.Â