The cholinergic system is an important modulator of brain processes. It contributes to the regulation of several cognitive functions and emotional states, hence altering behaviors. Previous works showed that cholinergic (nicotinic) receptors of the prefrontal cortex are needed for adapted social behaviors. However, these data were obtained in mutant mice that also present alterations of several neurotransmitter systems, in addition to the cholinergic system. ChAT-IRES-Cre mice, that express the Cre recombinase specifically in cholinergic neurons, are useful tools to investigate the role of the cholinergic circuits in behavior. However, their own behavioral phenotype has not yet been fully characterized, in particular social behavior. In addition, the consequences of aging on the cholinergic system of ChAT-IRES-Cre mice has never been studied, despite the fact that aging is known to compromise the cholinergic system efficiency. The aim of the current study was thus to characterize the social phenotype of ChAT-IRES-Cre mice both at young (2–3 months) and middle (10–11 months) ages. Our results reveal an alteration of the cholinergic system, evidenced by a decrease of ChAT, CHT and VAChT gene expression in the striatum of the mice, that was accompanied by mild social disturbances and a tendency towards anxiety. Aging decreased social dominance, without being amplified by the cholinergic alterations. Altogether, this study shows that ChAT-IRES-Cre mice are useful models for studying the cholinergic system‘s role in social behavior using appropriate modulating technics (optogenetic or DREADD).

Intraspecific color variation is often associated with camouflage or protection, but melanin-based color variation is also linked to behavioral and physiological aspects including boldness. In the melanin-based plumage color polymorphic tawny owl (Strix aluco), the grey morph is known to be more cryptic than the brown morph. Using 19 captive tawny owls (11 grey and 8 brown), we tested if these two color morphs that differ in camouflage tend to differently use exposed perches in a familiar environment (home aviary) and a novel environment (experimental aviary), as well as whether their response to predation risk and mobbing cues differs. The two color morphs did not differ in their exposure under known conditions (in their home aviary), but brown tawny owls were more likely to use exposed perches than grey tawny owls after release in a novel environment. Significance statement Melanin-based coloration can be associated with several behavioral traits. However, it is still unknown how predators with genetically-based color polymorphism vary in their efficiency of active background choice and risk-prone behavior while facing predation risk or mobbing harassment. Using captive tawny owls, we investigated predators’ behavior (attention towards the stimulus and use of space) while confronted to mobbing events and predation risk. We showed that tawny owls were using their space differently according to their color morph in a novel environment (experimental aviary) but not in a familiar environment (home aviary).