Like an owl in an ivy-bush. Having a sapient, vacant look, as some persons have when in their cups; having a stupid vacant stare. Owls are proverbial for their judge-like solemnity, and ivy is the favourite plant of Bacchus. Gray, in his Elegy, refers to the Owl and the Ivy.
From yonder ivy-mantled tower The moping owl doth to the moon complain Of such as, wandering near her secret bower, Molest her ancient solitary reign.
Source: Dictionary of Phrase and Fable, E. Cobham Brewer, 1894