Effects of herbivore-induced plant volatiles on behaviors and reproduction in a common songbird

In 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 in 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 to control ones, resulting in significantly
more eggs, nestlings, and fledglings introduced in 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
investigations. 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.