The literature on whether birds have vomero-nasal organs (VNO) in birds is confusing, with little hard evidence supporting the presence of the organ, but equally few firm rejections of its presence. The situation regarding dinosaurs is equally confusing; Tyrannosaurus rex apparently did not have a VNO, but some pterosaurs might have had one (at least, they have two currently unexplained palatal fossae). Is there any recognised definitive literature on this matter?
The only contribution that I can make is reference to a reasonably recent (2011) paper - "Chemical communication without a vomeronasal organ: parallel evolution in birds and primates" by Danielle Whittaker - it is free to download. A 1999 paper by Eric B. Keverne - "The Vomeronasal Organ" in Science, simply states that the organ does not exist in birds.
A review by Taniguchi shows that VNO is absent in fishes and birds [Journal of Veterinary Medical Science Vol. 73 (2011) No. 2 February P 139-147].
It is now well established that birds lack a vomeronasal organ/system. However, this seems to be a retained, ancestral (primitive) trait in archosaurs (crocodilians also lack a VNO—we can surmise that dinosaurs did, as well). In contrast, recent work shows that many birds have a highly developed main olfactory system (nasal olfaction via the nose). This is supported genomically, morphologically and behaviorally—in contrast to earlier views. Non-avian theropod dinosaurs also had relatively large olfactory bulbs. The review in JVMS noted above is terrible, by the way—leaves out most of the relevant literature and is full of errors. Just search on 'bird' and 'olfaction' to find lots of recent papers. Note—it is not necessary to have a functional VNO to receive pheromones. In many mammals, known pheromones are received via the nose.
I can not provide a paper regarding the topic. I realize that this a highly debated topic. Although as a aviculturist turned scientist, I would argue that they do. Here are some images you might find helpful.
http://www.scarletimaging.com/birds.html
http://www.avianstudios.com/the-grey-parrot-anatomy-project/images/
This is an empirical question that can be answered fairly directly. There is significant morphological, neuroanatomical and genomic evidence demonstrating that birds lack a vomeronasal system. Here are two quotes with sources:
"No report has ever been made of a vomeronasal system in a bird. In her extensive analyses of avian nasal cavities, Bang never found a functional or vestigial vomeronasal organ nor is there any sign of a vomeronasal nerve or an accessory olfactory bulb in those avian species used for neuroanatomic studies." (Wenzel, B.M. 1987. The olfactory and related systems in birds. Annals New York Acad. Sci. 519:137-149.)
"Both the zebra finch and the chicken genome assemblies lack genes encoding vomeronasal receptors, casein milk proteins, salivary-associated proteins and enamel proteins—not surprisingly, as birds lack vomeronasal organs, mammary glands and teeth." (Warren, W.C. et al. 2010. The genome of a song bird. Nature 464:757-762.)
Birds lack an accessory olfactory bulb, which is universally associated with the VNO (Reiner A, Karten HJ. 1985. Comparison of olfactory bulb projections in pigeons and turtles. Brain Behav Evol 27:11–27; also ANTONIO ABELL_AN, ESTER DESFILIS, AND LORETA MEDINA. 2013. The olfactory amygdala in amniotes: An evo-devo approach. Anatomical Record 296:1317-1332.)
The paper Wenzel cites is:
BANG, B. G. 1971. Functional anatomy of the olfactory system in 23 orders of birds. Acta Anat. 79 (Suppl.1): 1-76.
Since living crocodilians also lack a vomeronasal system, parsimony suggests that ALL archosaurs, including dinosaurs, lacked a VNO, with the possible exception of extremely basal members of the group (there is also no physical evidence for a VNO in fossil archosaurs either, but that is equivocal).
The question of living birds possessing a VNS is one for histological research. This is so because of the microscopic size of the elements. In the periphery, one hopes to find a neuroepithelium in the form of a duct or patch, and Kurt summarizes the necessary evidence on the accessory olfactory bulb. So the very nice images provided above on the grey parrot and other birds are simply too macroscopic for the job.
A pitfall in the search for vomeronasal structures is that serial histological sections are needed because sampling regions can lead to falsely proclaiming a VNS structure is absent (when in fact it remains hidden in unsampled regions). So, there may well be birds that have not been studied thoroughly enough. See the literature on the VNO in primates and bats to get a sense of the enormity of the task.
That said, I would definitely agree with Kurt that a VNS in birds is highly unlikely. What seems possible though, is that some vestige of the peripheral receptor organ (the VNO) may remain in at least some birds, as is the case for some mammals.
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