The bottom image shows non-reciprocal allopreening (the non-mutual preening of one individual exclusively by another of the same species, usually the mate or parent). This behavior has been documented in many bird species including the Carrion Crow (Harrison 1965, Summers-Smith 1959). It is often initiated by the male and is thought to establish or maintain a pair bond. Here the focus was the head of the second bird (presumably the female), an area where birds cannot preen themselves. The metallic blue sheen is characteristic of this species which has disjunct populations in Europe and East Asia with those in East Asia averaging larger than those in Europe. They are separated by a partly gray, but otherwise similar species, the Hooded Crow C. cornix. The two hybridize where they come into contact, but the hybrid offspring are at a selective disadvantage (Parkin et. al. 2003). Canon SX50 HS PowerShot.
References:
Haas, F., Pointer, M.A., Saino, N., Brodin, A., Mundy, N.I. & Hansson, B. (2009) An analysis of population genetic differentiation and genotype–phenotype association across the hybrid zone of carrion and hooded crows using microsatellites and MC1R. Mol. Ecol. 18(2): 294–305.
Harrison, C.J.O. 1965. Allopreening as agonistic behaviour. Behaviour 24: 161-209.
Londei, T. (2013) Alternation of clear-cut colour patterns in Corvus crow evolution accords with learning-dependent social selection against unusual-looking conspecifics. Ibis 155(3): 632–634.
Madge, S. (2017). Carrion Crow (Corvus corone). In: del Hoyo, J., Elliott, A., Sargatal, J., Christie, D.A. & de Juana, E. (eds.). Handbook of the Birds of the World Alive. Lynx Edicions, Barcelona. (retrieved from http://www.hbw.com/node/60794 on 7 June 2017).
Madge, S. & Burn, H. (1994) Crows and Jays: A Guide to the Crows, Jays and Magpies of the World. Houghton Mifflin, Boston.
Parkin, D. T., Collison, M., Helbig, A., Knox, A. G., & Sangster, G. (2003). The taxonomic status of Carrion and Hooded Crows. British Birds 96 (6): 274–290.
Rolando, A. (1993). A Study on the Hybridization between Carrion and Hooded Crow in Northwestern Italy. Ornis Scandinavica 24(1), 80-83. doi:10.2307/3676414
Summers-Smith, D. 1959. Co-operative preening by Carrion Crows. British Birds 52: 1640.