As we exit the 31 days of March, we can look back on a month that gave us the vernal equinox - the first day of spring - but much of the time, it seemed more like winter.

After a chilly start, the month progressed to warming and we went from subzero to 50s. The impressive snowpack due to a snowy February has shrunk considerably. We begin April with more than 12.5 hours of daylight, growing more each day. But we will probably get more cold and snow in this new month.

A few early migrants of eagles, hawks and geese may have arrived, but most others will be in the coming weeks. However; birds that wintered with us are showing responses to spring.

During my pre-dawn walks now, I hear the local barred and great horned owls proclaiming territorial ownership. Chickadees and nuthatches call in the yard and the finches, including redpolls that did not come to the feeders until March, are getting restless to move again.

Recently, I watched as six turkeys - five female and one male - came by the house. In the spring sunlight, the male fanned his tail in a courtship display. Though I have not seen them, I heard reports of waking raccoons, skunks and chipmunks. And in the 50-degree sunlight, a couple of hibernating butterflies may take flight as well.

But as we enter April, I find plants are worth observing. On south-facing sites of buildings, including our house, crocuses and dandelions open to this new season. Though these flowers add color to the scene, I also like to look at the trees. They stood out in the weather all winter and now are reacting to this spring month.

Sunlight absorbed by the dark bark of tree trunks radiates out to melt the surrounding snow forming "tree circles" at the base.

And this is the time of the sap flow. Other trees respond to the longer days in their own ways. While the small red-osier dogwoods form bright red twigs, some willows do the same while others hold yellow branches. Weeping willows are easy to see at this time.

Recently as I drove by a swamp, I noticed a tint of purple on the twigs of the speckled alder trees that grow here. Stopping for a closer look, I could see that the hot-dog shaped catkins that were on the branches all winter are now enlarging and taking on this purplish color. Soon, these structures will get bigger and show the yellow pollen that is produced here; in the male catkins.

April is the month of catkins. We saw furry buds of willows and quaking aspens opening about a month ago. Soon, they'll grow larger to form their male catkins and the subsequent pollen.

Catkins do not have petals or nectar, often associated with flowers, but they are the early spring flowers of trees. There are few insects around now to spread the pollen and so the trees take advantage of the breezes and produce pollen on the catkins that hang out in the open.

Pollen from the male catkins drifts off to land on the female parts. It begins now with the catkins of alder, but soon we will see catkins of willow, aspen and hazel with birch and ironwoods a bit later in the month. Silver maples are opening their buds now too, but with no catkins.

In May, we will see the tree leaves and showy blossoms, but tree flowering begins now with catkins of speckled alders.