Smaller passerines, often around the same size as the mice and voles popular in the diet, are also regularly reported as prey. Conspicuous nesting sites of barn swallow ("Hirundo rustica") and purple martin ("Progne subis") on manmade structures and objects were revealed via video-monitoring to suffer heavy predated by barred owls. In the case of the barn swallows, all ages of swallow as well as possibly eggs were eaten. 65 of 95 monitoring barn swallow nests were depredated by owls over a 3 year period. The muddy bank nests of cliff swallows ("Petrochelidon pyrrhonota") are also vulnerable to barred owls, while other swallow species are known to be opportunistically taken. In more enclosed wooded areas, radio-tagging and video-monitoring of various passerines nests as well as examinations of owl pellets has shed light on the relationship of barred owls with these potential prey resources. Not only was the barred owl found to be a surprisingly routine predator at woodland passerine nests, but that an unexpected bulk of the acts of predation in studies from Missouri and Illinois were carried out during the daytime. Many different forest bird species (most frequently in Missouri and Illinois on acadian flycatchers ("Empidonax virescens") and indigo buntings ("Passerina cyanea")) were thusly hunted. These studies indicated that the barred owl may snatch passerines of any age, but recent fledglings are taken preferentially due to their often more conspicuous behavior and lacking ability for flighted escape. In Minnesota, about 62% of studied hermit thrush ("Catharus guttatus") and ovenbird ("Seiurus aurocapilla") fledglings were taken per one study, with all thrush that nested in the radius of the barred owl’s nests failing to produce any young. A similarly high rate of local determent by barred owls has been found for other woodland thrushes like the veery ("Catharus fuscescens"), the wood thrush ("Hylocichla mustelina") and the varied thrush ("Ixoreus naevius"), with the additional finding that pre-dawn singing by certain thrushes, when their escape abilities are dulled by the dim light, endangers them to barred owl ambushes. Forest birds seem to recognize the barred owl as a threat, with mobbing behavior evoked easily by playing recordings of their calls in the daytime.