Effects of Herbivore-Induced Plant Volatiles on Behaviors and Reproduction in a Common Songbird

AbstractIn insectivorous birds the reproductive period often coincides with the spring development of vegetation, but whether there is a direct relationship between the two, and through which mechanisms this link could come about, is not clear. Trees release herbivore-induced plant volatiles (HIPVs) when they are attacked by insects, and we test here whether birds use those alarm odors to modulate their behaviors and their reproduction. Using a two-step experimental approach, we first show under controlled conditions that blue tits are attracted to HIPVs mimicking a caterpillar attack on downy oak buds in early spring without having to learn them. We then equipped nest boxes in the field with the same artificial HIPVs. We did not find that birds that built their nest in HIPV nest boxes advanced lay dates or produced larger clutches. However, although this result was not statistically significant, slightly more nest boxes equipped with HIPVs were occupied compared with control ones, resulting in significantly more eggs, nestlings, and fledglings introduced into the population from these treated nest boxes. Our results thus show that blue tits innately detect and track subtle plant olfactory signals, while the link with reproductive decisions appears more tenuous and requires further investigation. Such a link with reproduction is nevertheless in line with recent studies showing that HIPVs can stimulate the reproductive physiology of songbirds and highlights new multitrophic interactions across plants, insects, and birds, an encouraging area of study for understanding adaptations to a constantly changing environment.