While pruning my apple trees, I noticed an abundance of wild pearly everlasting (Anaphalis margaritacea) woven into one nest and wondered if the birds purposely used this fragrant, antiseptic herb. The Research Unit for Ornithology of the Max-Planck Society did find that European starlings mix fresh herbs—especially those rich in antiseptic essential oils—with their dry nest material. The birds were observed adding herbs to half of 148 nests. Both herb and nonherb nests contained the same number of mites, lice, and fleas, but nestlings in the herb nests weighed more, had higher hematocrit levels, and showed less immune activity against parasites, indicating that the herbs stimulated their immune systems and reduced parasites.
Source: Gwinner, H., et al. “Green plants in starling nests: effects on nestlings.” Animal Behavior 2000, 59(2): 301–309.