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The ability to recognize oneself is separate from recognizing a conspecific. Self-recognition is a higher cognitive function and generally tested by a mirror-mark paradigm, in which the individual recognizes and responds to an inconspicuously placed mark on body from its mirror-reflected image. Although initially suggested to be associated with large-brained mammals, the ability of self-recognition has now been shown in non-mammals, including fish and birds. Hence, studies on many more species might be useful to understand general principles and underlying mechanisms of the evolution of social intelligence. Here, we examined self-recognition ability in Indian house crows (Corvus splendens), by testing them first for mirror-induced responses and then for the mark-directed responses. A circular coloured mark was inconspicuously placed on the throat under the bill where crows could see it only from its mirror-reflected image; a similar black mark placed at identical location which was difficult to be seen served as the control condition. We evaluated how closely crows viewed and inspected the object, and expressed social, contingent and self-directed responses to the mirror and cardboard. Crows exhibited greater preference in response to the mark when in front of the mirror, compared to they were in front of the non-reflective black cardboard. The majority (4/6) crows responded to the mirror-reflected self-image, as evidenced by attempts to remove the coloured mark by using beak or claws; no such response was found in control condition. These results suggest self-recognition by Indian house crows, and support the growing evidence that the ability of self-recognition is more widely present among animals.

Under periodic day-night environment, most circadian functions maintain a close phase relationship relative to each other, suggesting a common circadian pacemaker control of different overt rhythms. In birds, this seems highly unlikely, given multioscillatory nature of the circadian pacemaker and downstream generation of several circadian behaviors. We hypothesized the dissociation of overt rhythms from circadian gene oscillations, if the two were loosely coupled, under an aperiodic light condition. We tested this in daily rhythms in singing, activity and clock gene expressions in adult male zebra finches (Taeniopygia guttata) that were born and raised under the constant light (LL; 24L:0D), with controls on an LD cycle (12L: 12D). Particularly, we monitored daily pattern of singing and activity behavior, and measured 24 h mRNA expression of immediate early gene (c-Fos), clock genes (Bmal1, Per2 and Rev-erb β) and epigenetic marker genes (Dnmt3b and Tet2) in the hypothalamus, and of clock genes and genes coding for the aromatase (Arom), androgen receptor (Ar) and dopamine receptor (Drd2) in the song control nuclei (Area X and HVC) and cerebellum (motor control region). We found persistence of daily rhythms in activity and singing in all birds under LD, but in only 70% (14/20) birds under LL; thus, both behaviors were arrhythmic in 30% (6/20) birds) under LL. The overall song quality was also declined under LL. The clock genes showed daily rhythms in the hypothalamus, song control nuclei (except Per2 in Area X) and cerebellum under LD, although with differences in peak expression times; however, there was loss of rhythmicity in clock genes (except Bmal1 in Area X and HVC) under LL. We also found daily Ar mRNA rhythm in the Area X and cerebellum under LD. These results demonstrate for the first time the persistence of clock gene oscillations in the song control brain regions and show the dissociation of circadian behavior from genetic oscillations in relation to an imposed light environment.

We investigated the consequence of no night environment (constant light, LL) on reproductive performance in zebra finches in the parent (P) and subsequent F1 generation. As a measure of the overall effects on the metabolic reproductive health, we monitored daily activity behaviour, recorded song and cheek patch size in males, and measured body size and hormone levels. As compared to controls under 12 h light: 12 h darkness (12:12 h LD), both P and F1 pairs showed a compromised reproductive success, as evidenced by fewer fledglings and viable offsprings with longer fledging durations, and increased offspring mortality with successive three clutches under LL. The overall negative effect of the no-night environment was increased in the F1generation. As compared to P pairs, F1pairs had more failed nesting and breeding attempts, took longer to initiate reproduction, incubated fewer eggs, produced fewer viable offspring with longer fledging duration, and showed increased offspring mortality. Consistent with negative reproductive effects, P males showed significant changes in the motif duration and other spectral features of song, and both F1 and F2 males copied poorly the song of their parent under LL. Plasma corticosterone and sex hormones (testosterone in males and estradiol in females) levels were significantly lower under LL. Daily plasma melatonin rhythm persisted but with a reduced amplitude under LL. These results demonstrate the importance of night in reproduction in a continuously breeding diurnal species, and give insights into the possible impact on physiology of animals whose surrounding environment is consistently losing the darkness of night.

Disruption of the cyclic feature of the day-night environment can cause negative effects on daily activity and advanced brain functions such as learning, memory and decision-making behaviour. These functions in songbirds, including corvids, involve the hippocampus, pallium and midbrain, as revealed by ZENK (a neuronal activation marker) and tyrosine hydroxylase (TH) expressions. TH is rate-limiting marker enzyme of the biosynthesis of dopamine, widely implicated in learning and memory. Here, we measured ZENK and TH immunoreactivity in the hippocampal, pallial and midbrain regions in response to cognitive performance (learning-memory retrieval) tests in Indian house crows ( Corvus splendens ) exposed to constant light environment (LL) with controls on 12 h light:12 h darkness. Along with the decay of circadian rhythm in activity behaviour, LL caused a significant decline in the cognitive performance. There was also a decrease under LL in the activity of neurons in the hippocampus, medial and central caudal nidopallium, and hyperpallium apicale, which are widely distributed with TH-immunoreactive fibres. Further, under LL, TH- immunoreactive neurons were reduced in number in midbrain dopamine synthesis sites, the venteral tegmental area (VTA) and substantia nigra (SN), with a negative correlation of co-localized ZENK/TH- immunoreactive cells on errors during the association tasks. These results show decreased activity of learning and memory neural systems, and underscore the role of dopamine in reduced cognitive performance of diurnal corvids with disrupted circadian rhythms under an abrupt light environment.

We investigated the temperature effects on hypothalamic transcription of genes involved in the induction of photoperiodic response in redheaded buntings. Birds were exposed at 22 and 38 °C to 13-h long photoperiods (LP), with controls at 22 °C on 8-h short photoperiods (SP). At 22 °C, compared to SP, we found higher tshb, eya3 and dio2 and low dio3 and gnih mRNA expressions after a week of LP; concomitant with testis recrudescence this confirmed buntings’ responsiveness to LP-induced photostimulation. tshb, dio2 and gnrh mRNA levels were further increased by 2.5 weeks of LP at 38 °C. Temperature sensitive trpm8, but not trpv4, bdnf or adcyap1 also showed LP-induced expression at 22 °C. Concomitant changes in dnmt3b and tet2 mRNA expressions further suggested epigenetic modification of temperature influence on photoperiodic responses. These results demonstrate the role of temperature in hypothalamic molecular regulation of the photoperiodic gonadal response in seasonally breeding birds.

Artificial light at night induces circadian disruptions and causes cognitive impairment and mood disorders; yet very little is known about the neural and molecular correlates of these effects in diurnal animals. We manipulated the night environment and examined cellular and molecular changes in hippocampus, the brain region involved in cognition and mood, of Indian house crows (Corvus splendens) exposed to 12 hr light (150 lux): 12 hr darkness (0 lux). Diurnal corvids are an ideal model species with cognitive abilities at par with mammals. Dim light (6 lux) at night (dLAN) altered daily activity:rest pattern, reduced sleep, and induced depressive-like responses (decreased eating and self-grooming, self-mutilation, and reduced novel object exploration); return to an absolute dark night reversed these negative effects. dLAN suppressed nocturnal melatonin levels; however, diurnal corticosterone levels were unaffected. Concomitant reduction of immunoreactivity for DCX and BDNF suggested dLAN-induced suppression of hippocampal neurogenesis and compromised neuronal health. dLAN also negatively influenced hippocampal expression of genes associated with depressive-like responses (bdnf, il-1β, tnfr1, nr4a2), but not of those associated with neuronal plasticity (egr1, creb, syngap, syn2, grin2a, grin2b), cellular oxidative stress (gst, sod3, cat1) and neuronal death (caspase2, caspase3, foxo3). Furthermore, we envisaged the role of BDNF and showed epigenetic modification of bdnf gene by decreased histone H3 acetylation and increased hdac4 expression under dLAN. These results demonstrate transcriptional and epigenetic bases of dLAN-induced negative effects in diurnal crows, and provide insights into the risks of exposure to illuminated nights to animals including humans in an urban setting.

Periodic day-night environment shapes the temporal pattern in the behaviour and physiology (e.g. 24-h activity-rest and sleep-wake cycles) and the advanced brain function, such as learning, memory and decision making. In a previous study, we showed the abolition of 24-h rhythm in the activity-rest pattern, and an attenuated cognitive performance in diurnal Indian house crows (Corvus splendens) under constant light (no-night; LL) environment. Present study extended this, and investigated LL-induced effects on the neurogenesis (birth, maturation and neurite complexity of new born neurons) in the hippocampus and caudal nidopallium, the brain regions directly associated with learning and cognition in birds. We performed immunohistochemistry of doublecortin (DCX; a neurogenesis marker) and tyrosine hydroxylase (TH, a key enzyme of the dopamine biosynthesis) in the brain section containing hippocampus or caudal nidopallium of Indian house crows exposed for 2 weeks to LL, with controls maintained under 12L:12D. As expected, crows showed arrhythmicity with a significantly reduced rest period in the 24-h activity-rest pattern, and a decreased cognitive performance when tested for the spatial and pattern association learning tasks under LL. Importantly, there was a significant decrease in DCX-immunoreactive (ir) cells and, as shown by Sholl analysis, in the complexity of DCX-ir neurites in both, the hippocampus and caudal nidopallium of crows under LL, as compared to those under 12L:12D. The anatomical proximity of DCX-ir neurons with TH-ir fibers suggested a functional association of the new born hippocampal and caudal nidopallial neurons with the learning, and perhaps cognition in Indian house crows. These results give insights into possible impact of the loss of night on brain health and functions in an emerging ecosystem in which other diurnal species including humans may be inadvertently exposed to an illuminated night, such as in an overly lighted metropolitan urban habitat.