Winter Birds in the ArboretumSUNDAY, DECEMBER 11, 2011
As usually happens sometime in late Fall, often a week or two after Thanksgiving, we experience a spell of cold freezing temperatures. The highs barely get up to the twenties and the lows go down to single digits Fahrenheit. This is the time when the open water on Lake Wingra freezes; except for where there are springs or a late flock of Canada Geese keeps a small patch of water open by paddling around it through the night.
How are our woodland, prairie and water birds able to survive the winter here? Feathers, which are unique to birds and distinguish the Class Avies, have a lot to do with birds being able to stay over winter. All birds have feathers and only birds have them. Feathers permit flight in most birds and can be specialized for many different functions. Down feathers are modified for insulating birds. If you have ever worn a garment insulated by down feathers, you know how warm these feathers are due to their ability to trap warm air near the body. When combined with other feathers, such as wing feathers that fold around the body, our winter birds are able to maintain a warm core body temperature even in below zero temperatures.
Feathers also permit birds to fly rather quickly from areas where they roost to areas where they feed. Some birds do both in the same area, such as woodpeckers, who roost in cavities in trees and feed on insect larvae and other things on tree trunks and branches. Many birds fly to food sources away from where they roost. The few remaining geese will fly a fair distance to feed in fields on grain and seeds, then return to open water to roost for the night. Gulls and Crows often feed a distance from where they roost.
Some of the smaller birds, Chickadees, Cardinals, Nuthatches, Finches and Sparrows leave the areas where they spend the night roosting in bushes for protection from the cold and wind to feed at bird feeders. We have no bird feeders at the Arboretum, so we do not have a concentration of easy to see winter birds. Many of the houses in the neighborhoods around the Arboretum have bird feeders, which attract birds that find night shelter here.
What do our winter birds eat? Most of the perching birds that over winter here eat seeds, fruits or insect larvae and eggs. This includes Cardinals, Goldfinches, House Finches, and Sparrows, who all have beaks capable of cracking seeds. The woodpeckers have special adaptations that permit them to chisel into wood for insects and insect larvae and eggs. Their beaks are modified, their tongues are longer and attached to the back of the skull and their tail feathers are stiff, to allow them to perch upright on tree trunks and branches. Our three common woodpeckers are the Downy, Hairy and Red-bellied. Occasionally the crow-sized Pileated Woodpecker can be heard and, less often, seen in the older woods. On the prairies and along the edges between open and woodland habitats are Goldfinches and Tree Sparrows. They feed on small seeds.
Birds need water even in the winter. The springs around Lake Wingra and places were flowing water does not freeze provide over wintering Arboretum birds with water. This availability of water and fruit from fruiting trees in Longenecker Garden and from native and invasive trees and bushes allows some Robins and Cedar Waxwings to over winter.
If one is lucky a bird of prey, such as a Red-tailed Hawk, Cooper’s Hawk or one of our three resident owls, Eastern Screech, Barred or Great Horned, can be seen or heard. These larger predatory birds feed on small rodents and birds, with the larger hawks and owls catching squirrels or rabbits. Before our walk today the resident Red-tailed Hawk flew from a perch on the large metal sign near the entrance to Curtis Prairie down to the lawn between the prairie and the parking lot, grabbed a small rodent and flew up to a nearby oak where the bird devoured its prey.
There are only a few dozen bird species and not very many of each over wintering here because the resources they need, food, water and shelter, are rather limited. I suspect by feeding birds, people have increased the numbers of some winter birds. This can be an enjoyable way to view winter birds and a warmer way for the viewer than to walk the trails of the Arboretum in search of winter birds. But to see many of our winter birds you need to bundle up and venture forth through the various Arboretum plant communities.
Levi E. Wood