Betula pendula scales. The foliage is a pale to medium green and turns yellow early in the autumn before the leaves fall. In mid-summer, the female catkins mature and the male catkins expand and release pollen, and wind pollination takes place. The small 1 to 2 mm winged seeds ripen in late summer on pendulous, cylindrical catkins long and broad. The seeds are very numerous and are separated by scales, and when ripe, the whole catkin disintegrates and the seeds are spread widely by the wind. Silver birch can easily be confused with the similar downy birch ("Betula pubescens"). Yet, downy birch
Northern rough-winged swallow Northern rough-winged swallow The northern rough-winged swallow ("Stelgidopteryx serripennis") is a small, migratory swallow. It is very similar to the southern rough-winged swallow, "Stelgidopteryx ruficollis". The genus name, "Stelgidopteryx", is from Ancient Greek and means "scraper wing" and the species name, "serripennis", is derived from Latin and means "saw feather". In the common name, "rough-winged" refers to the serrated edge feathers on the wing of this bird; this feature would only be apparent when holding this bird. Six subspecies of the northern rough-winged swallow are currently recognized. It has been proposed that another race be recognized, "aphracta", but this is