Until recently the conventional wisdom was that birds were not very intelligent. But this view is changing. Especially the crow, parrot, owl and woodpecker families contain some very intelligent species. Some of these birds show traits that imply brains as powerful as the smarter mammals. The list is amazing: using tools, making tools, powerful spatial memory, logical reasoning, communication, social behaviour in family and larger groups, cooperation, consoling behaviour, counter-espionage showing a theory of mind, passing the mirror test for self awareness, an artistic talent. Relative to body weight, a crow has as big a brain as a chimp. Not only are they comparable to mammals in their intelligence, they also seem to have a similar sort of intelligence. So it is probably that they have a similar sort of consciousness as primates, dolphins, dogs, elephants and the like.
But there is a rub. A birds brain is very different from a mammals. Here is the intro to Gunturkuns 2005 paper (please supply umlauts on all us in the name) The avian prefrontal cortex and cognition.
Mammals such as humans, macaques or rats can adjust their behaviour to changing demands. They are capable of reversing learned behavioral choices, selecting appropriate responses according to contextual information, and withholding actions until a suitable situation occurs. In short, they optimally organize their behaviour over time. The set of cognitive skills required for this behavioural optimization is called executive functions and is associated with the operations of the prefrontal cortex. The phylogenetic success of the order of mammals is probably related to the extraordinary cognitive flexibility that is generated by prefrontal circuits. Birds represent a broadly equally successful vertebrate order and a vast literature on avian cognitive skills testifies that birds are able to generate the same set of executive functions as mammals. However, birds and mammals differ substantially with regard to the organization of their forebrains, with birds lacking a laminated cortex. So, which neutal mechanisms do birds use to generate cognitive functions for which the prefrontal cortex is required in mammals?
He goes on to examine the structure of the two brain types (mammal and bird). Of course, they share the basic vertebrate pattern of a three part brain (forebrain, midbrain and hindbrain). The hindbrain, midbrain and the basal nuclei of the forebrain are highly conserved through evolution. It is in the rest of the forebrain that birds and mammals differ. Rather than our neocortex, birds have the neostriatum. Interestingly the connections, neurotransmitters, and functions of these two structures are similar. In particular the executive functions have been compared in the prefrontal cortex (PFC) and the nidopallium caudolaterale (NCL) part of the neostriatum.
The mammalian PFC and the avian NCL show an astonishing degree of resemblance in terms of anatomical, neurochemical, electrophysiological and cognitive characteristics. Based on topographical and genetic arguments, however, they do not seem to be homologous as a telencephalic entity within the pallium but probably represent a case of evolutionary convergence in terms of neuronal circuits as paralleled by recent studies that clearly reveal that, in particular, corvids (crows) and parrots are able to generate cognitive abilities identical to apes. Emery and Clayton argue that these common cognitive operations derive from a shared cognitive tool kit consisting of causal reasoning, flexibility, imagination and perspective. Most of these shared cognitions thus depend on the PFC and the NCL This makes it likely that there exist only very limited neural solutions for the realization of higher cognitive functions.
I see another possibility. Maybe the root of the tool kit is in the older parts of the forebrain (not the PFC or NCL but the basal nuclei and thalamus) that communicate with either the PFC or the NCL. It would be like the tool kit has a computer to use in both mammals and birds but the computer was created from enlargement of different parts of the basal nuclei in the two types of vertebrate.
Also I presume that the tool kit also includes consciousness.