The ability to require food is what determines whether birds stay in the winter or not.
This collection of photos were all taken in my backyard. These are some of the hardy birds that stick around during cold winter weather in Philadelphia and elsewhere.
There are only 20 -30 land birds (common and easily found), which stay in cold winter in North America.
These birds will feed on seeds of grasses, flowers, trees, and shrubs, on the still hanging fruit of fall-fruiting shrubs. And on the insect eggs and hibernating insects are hidden in the nooks and crannies of trees and shrubs.
In winter there are no airborne insects for aerial feeders like warblers, swifts, and flycatchers, so these birds go where the insects are hovering in the air, Central and South America.
Slowly moving water like ponds and lakes, freeze over in cold weather. So the ducks, herons, rails, and sandpipers move to open, unfrozen water.
In Philadelphia, these birds can be found along the Delaware and other Rivers, in Tinicum Marsh and the Atlantic Ocean along the Jersey and Delaware shores.
Of the birds pictured in the collage above, the Dark-eyed Juncos migrates to the Philadelphia area and Delaware Valley. The Juncos breed in conifer forest far to the north and migrate south in the fall. They spend the winter from southern Canada to the Gulf of Mexico.
Each fall I look for them underneath the shrubs in my backyard. When they arrive it is a clear sign the wheel of the seasons is turning and living beings are following their instructions on how to live.
Top left: Mourning Dove, top right: Dark-eyed Junco
Lower left: male Cardinal, lower right: Chickadee (Carolina/Black-capped, I live in an area were they hybridize)