By ROBERT DRYJA
Los Alamos

Both plants and birds pass through transitions when the first cold fronts of winter are arriving. The change of leaf color is the most visible change for plants. This change does not move in lock step with all plants changing their leaf color at the same time. Some trees shed all their leaves by late October while other still have green leaves in mid November. This difference for autumn leaves is particularly visible when the first snow fall arrives. The expectation is to see bare branches. It then is somewhat startling to see branches with green leaves also covered with snow.

Why do some trees or bushes keep green leaves well into autumn? Why do other plants become dormant with no leaves in early autumn? Green leaves mean that photosynthesis is occurring. A tree can still be creating nutrients that are stored for next spring and immediately available for growing new leaves and branches. An early autumn dormant tree needs to first grow new leaves in the spring before it can start new branches or flowers.

Birds also have changes in their behavior. Red winged blackbirds gather in groups as they fly away from higher mountain country. The groups are leaving areas that colder and more likely to have snow. They may sense the increasing air pressure of a cold front as it approaches. Flocks therefore may gather on tree tops and then fly on to lower and somewhat warmer areas just before snow arrives. It is impressive to see a flock of thirty to forty red winged black birds fly as group to a tree and then fly away from it later.

Black-eyed juncos tend to live separately in the summer. Male juncos claim areas for nesting and chase others away. This behavior changes with the arrival of winter. Flocks now develop. A bird feeder may have fifteen or more juncos around it while they look for food. The feeder in contrast may have had only one or two juncos present at one time during the summer.

Other species of birds also may appear at a bird feeder. White winged doves and collared doves are more likely to be seen high in trees during the summer. Spotted towhees usually hide in bushes. Canyon towhees usually remain on the ground, scurrying to hide under low lying branches. They now may appear in the open area around a feeder while looking for seed to eat.

The most surprising is the arrival of a cooper’s hawk. It may fly around a feeder for a few seconds because it is hunting for one of the other birds that have come for food. It approaches with stiff wing beats and circles a feeder in a tight glide.

A flock of red-winged black birds have gathered in the upper branches of a tall tree that has shed its leaves for winter. Photo by Robert Dryja

This species of tree still has green leaves even though snow has fallen. Photo by Robert Dryja

Five black-eyed juncos have gathered in and around a feeder. A sixth junco waits below the feeder for its turn to feed. Snow appears as faint white lines as it falls by the feeder. Photo by Robert Dryja