The Latin word "arbor" means tree. The last Friday in April is National Arbor Day, a day set aside for people to learn about trees and to plant trees in their communities.

Friday marks the 150th anniversary of the first Arbor Day, started in Nebraska in 1871. Just think, trees give us beauty, building materials and food, they shade and protect us, provide habitat for wildlife, and help clean air and protect water.

Some other observations this week:

Last year in southern Minnesota, during the final week of April, farmers were planting corn; spring wheat had started to emerge; gardeners pulled rhubarb to make sauce; we saw the first Canada goose goslings; daffodils and tulips were blooming; and native sugar maples began to leaf out.

Many of us experienced our first 70-degree day last Saturday, but below-normal temperatures, strong winds and cloudy skies have been the norm this spring across the Upper Midwest. Still, bird migration continues and with it, fox sparrows, hermit thrushes, turkey vultures and ring-billed gulls. They are reaching far northeastern Minnesota, where snow still can be found and more than 30 inches of ice continues to cover lakes.

In southern Minnesota, the white trout-lily and bloodroot bloom in forests and pasqueflower on prairies. The first belted kingfishers, brown thrashers and purple martins have returned. And white-throated sparrows are moving through.

Now is when we look for the "big three" (Baltimore oriole, ruby-throated hummingbird and rose-breasted grosbeak) to return to our yards and parks. An early returning male rose-breasted grosbeak arrived last Sunday in Le Sueur, Minn. These grosbeaks winter from Mexico to northern South America.

Even in this cold April, there are Canada geese, wood ducks and mallards incubating eggs. We usually see the first goslings and mallard ducklings by the end of April, but I'm sure It won't happen until the first week in May this year.

Mallard nests are on dry ground among dead grasses and other plants at the edges of marshes, ponds and lakes. Occasionally nests are built in school courtyards or under shrubs close to entrances to our homes, or in forks of trees, or on top of an old hawk nest, sometimes as high as 25 feet off the ground. The nest itself is built with grasses and leaves or any convenient material, and lined with down from the breast of the female.

Normally eight to 12 eggs — one per day — are laid. The female incubates alone. The eggs hatch in 26 days. Incubation starts with the laying of the last egg so that all the eggs will hatch on the same day. The drakes take no interest in family care after the eggs are laid. As soon as the ducklings dry off after hatching, their mother leads them to water. There she teaches her young to find food and to stay close to her for protection.

Jim Gilbert has taught and worked as a naturalist for more than 50 years.