Does the presence of a conspecific increase or decrease fear? Neophobia and habituation in zebra finches

Neophobia, defined as the fear of novelty, can be exhibited when
individuals encounter unfamiliar stimuli in their environment. Neophobia
has been shown to both increase and decrease when individuals are with
conspecifics. An increase in latency to contact new objects can be
explained by the negotiation hypothesis which proposes that individuals in
groups will negotiate who will approach novelty first, thereby delaying
the first contact. This negotiation process could co-occur with and mask a
potential effect of risk dilution, where individuals in groups should
approach novel objects faster due to lower perceived risk in a social than
non-social context. Here, we aim to test the risk dilution hypothesis
using an experimental set-up that precluded negotiation among group
members by physically separating dyads during social trials. We presented
zebra finches (Taeniopygia guttata) with different novel objects in both
social and non-social contexts. We also repeated the presentation of each
object to investigate, for the first time to our knowledge, the effect of
social context on the change in neophobia over repeated encounters (i.e.,
habituation). We found that social context increased the latency to
approach a novel object upon first presentation of objects (i.e.,
increased neophobia), but these latencies decreased faster over repeated
presentations of the objects (i.e., faster habituation) compared to the
non-social context. These results do not provide support for the risk
dilution hypothesis regarding first encounters with objects (neophobia)
but seem to support it over repeated object presentations (habituation).
This suggests that the effect of social context is different on neophobia
and habituation, possibly because they recruit different cognitive
mechanisms. Future studies should investigate the impact of ecological and
social conditions on decision-making upon first versus subsequent
encounters with a novel object in social animals, as both processes can
impact fitness costs and benefits of novelty
responses.