The crows install them upside down, to avoid the pokey bits themselves and apparently just as a structural support. The magpies install tons of them right side

The crows install them upside down, to avoid the pokey bits themselves and apparently just as a structural support. The magpies install tons of them right side up, apparently to turn their domed nest into a spike fortified bunker. For some reason I assumed bother of them were using them as defensive structures.