BEAR’S HIBERNATION 
In cold climates bears sleep through most of the winter in individual dens made in caves or holes in the ground. This sleep is not a true hibernation, 但短文说是冬眠！ as the bear’s metabolism remains in a normal state and it may wake and emerge during warm spells. The young, usually twins, are born during winter in a very immature state. Cubs stay with their mothers for about a year, and females usually mate only every other year.
 
WOOPECKER 
The sapsuckers (e.g., the red-breasted and yellow-bellied sapsuckers) may damage or kill trees by girdling them with small holes through which they eat some of the cambium and drink sap; they also feed on ants and wild fruit.
 
SOIL EROSION
In the United States 30% is natural erosion, while 70% is because of human intervention. Suspended sediment from erosion is one of the world’s greatest pollutants. Sediment can fill reservoirs and navigable waterways, impair wildlife habitats, increase flooding and water treatment costs, and deplete valuable topsoil. It can also concentrate harmful chemicals and bacteria. Among the methods of preventing soil erosion are reforestation, maintenance of fallow strips, terracing, underdraining, ditching, deep plowing, and plowing across slopes rather than up and down.