Natural Curiosities

Q.When a beaver cuts down a small tree, the tree stops growing. But if you saw down the tree, it sends out new sucker branches. Why?

Gary Bathke
Wells

A. If you observed a difference in trees' ability to regrow, it might have to do with the kind of tree, suggests DNR forester Dave Schuller: While aspen sprouts from the roots and birch sprouts from the stump, pine doesn't sprout at all. Or it could be a matter of the stump's surroundings. For sprouting to occur, light and heat must strike the stump or root area. If the beaver removed just one tree, shade from neighboring trees might prevent regrowth.

Q.When blue jays and crows come to my bird feeder, they rake seeds onto the ground. Sometimes I feel like they've made a pact with the squirrels to provide them with a constant food supply. I tried putting crossbars on the tray but then the old hulls build up and keep the fresh food from running down from the seed holder. Any suggestions?

David DeVoto
Stacy

A.Wildlife educator Jan Welsh says she had the same conspiracy taking place at her feeding stations until she switched feeder designs. Welsh puts her sunflower seed in a large cylindrical feeder surrounded by a seed cage made of material similar to 1-inch-grid metal hardware cloth. The cage lets the smaller birds in and keeps out the jays, crows, and squirrels.

Q.We have a 14-foot-tall bur oak in our yard. It gets plenty of water and nutrients and has been very healthy. Last December woodpeckers started tearing off the bark. Why are they doing this?

Tom Lorenz
Nashwauk

A.The woodpeckers are most likely a symptom rather than cause of the tree's decline, says DNR forest health specialist Susan Burks. Woodpeckers peck at trees to get at insects living there. But they rarely do this much damage unless the tree is infested with wood borers or bark beetles. Because these insects usually attack trees that are already stressed, the real culprit is likely something else, such as root damage or weather extremes. "The bugs and birds just take advantage of the opportunity, being the good recyclers that they are," Burks says.

Q.My son called me at work to say there was a pheasant eating a squirrel in our yard. He said the bird was about 12 inches high and that the tail feathers were short and reddish brown. I guessed it was a red-tailed hawk. Is it common for a hawk to come within a few feet of a house?

Rick Sather
Lakeville

A.It's not as unusual as you might think. Red-tailed hawks are common in the Lakeville vicinity. Because they have grown up in a populated area, they are not shy of houses or other human accoutrements. Red-tailed hawks eat small rodents, rabbits, amphibians, and snakes as well as squirrels.

Q.On a warm night on Big Deep Lake by Hackensack, we heard doglike sounds coming from the lake. The sounds were steady in pitch, and sounded like a whomp or a low bark. One person said they were dogfish. Others said they were turtles or frogs. Do you have any ideas?

Mike and Elaine Graupmann
Plato

A.Best guess would be a green frog or mink frog. The green frog sounds like a twanging banjo. The mink frog sounds like someone knocking on a wooden door. Listen to them at Green Frog and Mink Frog. By the way, your friend with the dogfish theory was not too far afield: Dogfish do indeed make a croaking sort of sound when out of the water.

Q.On a trip from Chicago to the Twin Cities last January, we saw 20 or more hawks perched in prominent places next to the freeway. Do the hawks congregate in larger numbers near the freeways for some reason, or is this just part of their normal distribution?

Jeffrey Wells
Minneapolis

A.The birds you saw were likely red-tailed hawks on the lookout for small rodents and rabbits. The wide-open views along highway rights of way provide a perfect place for hawks to hunt.

Q.Does plastic decompose into dirt? And if it does, would anything grow in the dirt?

Isaac Swenson,
Hopkins

A. Ordinary plastics buried in modern landfills are likely to remain intact for many decades, says Jim Chiles, policy analyst for the Minnesota Pollution Control Agency. Special, "compostable" plastics can break down in a matter of months if they are exposed to oxygen, water, and decomposing bacteria-but if these conditions are not present, they may not break down in landfills, either. Aside from additives such as colorants and plasticizers, the plastics found in consumer and food packaging wouldn't affect soil chemistry or prevent plants from growing there.