Animals enhance survival by synchronizing their internal circadian rhythms with regular and recurring environmental cycles, and this ensures physiological and behavioural activities to occur at the best-suited time within the 24-h day. Many species use light–dark cycle as the primary cue, but the other rhythmic signals such as cycles in temperature and food availability, and social interactions can play significant roles in timing the daily activities (Aschoff, 1981). Circadian rhythms in appropriate phase with one or several concurrently recurring environmental signals enable individuals to anticipate and prepare for the forthcoming challenges in their environment (Aschoff, 1981). Hence, a desynchrony between internal circadian rhythms and the external environment can negatively affect the physiology, behaviour and higher-order brain functions, and may compromise eventually the survival of individuals and species.

There is growing evidence that social cues influence both circadian (Levine et al., 2002; Davidson and Menaker, 2003; Singh et al., 2010) and non-circadian (e.g., communication- Woolley and Doupe, 2008; reproduction- Trainor et al., 2006; survival- Singh et al., 2010) functions. For example, Drosophila melanogaster adjusted its circadian locomotor rhythms based on prior social experience, such as housing with the conspecifics (Levine et al., 2002). Similarly, house sparrows (Passer domesticus) in a larger group showed greater success in solving the innovative problem-solving task (Liker and Bókony, 2009). Likewise, cage sharing with a conspecific influenced circadian rhythms and enhanced survival, as evidenced by 24-h activity behaviour and reduced mortality in redheaded buntings (Emberiza bruniceps) subjected to a challenging feeding regime (Singh et al., 2010). Thus, conspecific interactions can improve individual performance in the face of a challenging environmental condition (Jullien and Clobert, 2000). However, this has not been examined in the context of a temporally disrupted environment, such as the night-light pollution, which blurs the boundaries between light and dark periods within the 24-h day. Night-light pollution is widespread and affects a large proportion of the global population (Falchi et al., 2016).

Experimentally, exposure to dim light at night (dLAN) disrupts sleep-wake cycles, feeding behaviour, hormone secretion, metabolism, and cognitive performance in birds, particularly Indian house crow (Corvus splendens) and zebra finch, Taeniopygia guttata (Taufique et al., 2018; Batra et al., 2019, Batra et al., 2020, Batra et al., 2022; Buniyaadi et al., 2022, Buniyaadi et al., 2025a, Buniyaadi et al., 2025b). Notably, such avian studies have often overlooked the potential advantages, if any, of group living and conspecific social interaction in a social species. The key question is, therefore, whether living in group could mitigate the deleterious effects of the night-light-pollution environment in a social bird species. To answer this, we found Indian house crow (Corvus splendens) as an ideal experimental system. Crows are a highly social species and show pronounced effects of the ∼6 lx dLAN on sleep, mood, and high-order brain functions like the learning and memory consolidation, and performance in the innovative problem-solving task (Taufique et al., 2018, Taufique et al., 2019; Buniyaadi et al., 2022, Buniyaadi et al., 2025a). Hence, building on our previous studies, we hypothesized that the social enrichment via group housing would buffer the detrimental effects of the dLAN on behavioural and neurocognitive outcomes in house crows. The prediction was that crows sharing a cage with two other conspecifics would show mitigation of much, if not all, of the negative effects of a dLAN environment because of mutual conspecific interactions would act as a secondary time cue. Indeed, there is evidence for the social synchronization of circadian activity rhythms in house sparrows (Menaker and Eskin, 1966), and the influence of females on the restoration of rhythmic activity and singing in arrhythmic male zebra finches under the constant light condition (Jha and Kumar, 2017). At the same time, however, shared housing may disrupt functions like sleep, which requires a relatively stable environment.

Here, we assessed the effects of social grouping on plasma melatonin levels, and behavioural measures of sleep (quality and amount of nocturnal sleep), mood (feeding, preening (self-grooming), and depressive-like behaviour (self-mutilation), and cognitive performance shown by motivation skills in solving an innovative task in house crows exposed to the dLAN environment. To assess the effects at the mechanistic level, we also measured the mRNA expression of a few candidate genes chosen a priori, based on their reported roles in regulation of sleep, mood and cognitive performances in this species (Taufique et al., 2018; Buniyaadi et al., 2022, Buniyaadi et al., 2025a). This included genes coding for brain-derived neurotrophic factor (bdnf), doublecortin (dcx), nuclear receptor (Nr4a) family (nr4a2), tumor necrosis factor α (tnfα), interleukin 1ß (il-1ß) and tnf receptor 1 (tnfr1) in hippocampus, and genes coding for early growth response protein 1 (egr1), tyrosine hydroxylase (th), dopamine receptor 1 (drd1), dopamine- and cAMP-regulated phosphoprotein, Mr. 32 kDa (darpp32) as well as bdnf and dcx genes in the nidopallium caudolaterale and midbrain (substantia nigra and ventral tegmental area) regions. More specifically, bdnf, dcx and egr1 mRNA levels were used as indices of the neurogenesis and synaptic plasticity (Klempin et al., 2011; Duclot and Kabbaj, 2017; Taufique et al., 2018; Buniyaadi et al., 2022). For example, hippocampal bdnf mRNA levels were decreased concurrently with a compromised novelty exploration and exhibition of depressive-like response in house crows exposed to 6-lx dLAN (Taufique et al., 2018). Hippocampal bdnf mRNA levels were also correlated with the acquisition of spatial learning in rodents (Lu et al., 2014). Similarly, in parallel with learning and memory deficits, the DCX-immunoreactivity (DCX-ir) was decreased in house crows exposed to constant light, LL (Taufique et al., 2018). A proximity of DCX-ir and TH-ir neurons in the nidopallium caudolaterale indicates a potential functional relationship with the learning and cognition in house crows (Taufique and Kumar, 2016). Furthermore, th, drd1 and darpp-32 gene expressions reflect the activity of the catecholamine-synthesizing enzyme TH and the functioning of the dopaminergic system. They can thus serve as markers of the dopamine synthesis (Durstewitz et al., 1999), with the receptor activity playing a key role in the dopamine-mediated cognition, anti-depressive effects (Hare et al., 2019), as well as in the synaptic plasticity and reward-based learning (Sumiyoshi et al., 2014).