Effects of time and nest-site characteristics on concealment of songbird nests

We studied the effect of time and nest-site characteristics on nest concealment measurements and analyzed differences in concealment between parasitized, nonparasitized, depredated, and fledged nests. Mean concealment at nests of three old-field bird species was best explained by bird species, nest plant and height of the nest. Nests lost concealment over time, particularly those placed high in shrubs or roses (Rosa spp.). Mean and minimum concealment did not explain occurrence of predation or brood parasitism for any of the three bird species, and concealment at parasitized versus unparasitized nests and depredated versus fledged nests did not change differently over time. A literature review showed that most studies of real passerine nests using visual nest concealment have taken measurements after nest termination, and few studies indicated that concealment was important in explaining nest predation or brood parasitism. Late concealment measurements may be an additional source of error in nesting studies, especially if predation or parasitism is more likely to occur at nests sharing similar vegetation characteristics.