The widespread Cliff Swallow (Petrochelidon pyrrhonota) attaches its retort-shaped mud nests to cliffs, cave entrances, and a variety of artificial substrates, but the use of tree trunks and limbs for nest attachment has rarely been reported (Brown and Brown 1995). Nevertheless, Cliff Swallow colonies on yellow pines (Pinus ponderosa and/or P. jeffreyi) were long ago documented in the Big Bear Lake area of the San Bernardino Mountains, California, by Grinnell (1908; photographs), Willett (1912), and Dawson (1923; photographs). These authors did not specify the exact location(s) of the tree colonies within the Big Bear Valley; Dawson (1923) attributed the use of tree substrates to the lack of other suitable substrates in an “otherwise delectable country.”