Anatomical Specializations for Enhanced Olfactory Sensitivity in Kiwi, <b><i>Apteryx mantelli</i></b>

Abstract

The ability to function in a nocturnal and ground-dwelling niche requires a unique set of sensory specializations. The New Zealand kiwi has shifted away from vision, instead relying on auditory and tactile stimuli to function in its environment and locate prey. Behavioral evidence suggests that kiwi also rely on their sense of smell, using olfactory cues in foraging and possibly also in communication and social interactions. Anatomical studies appear to support these observations: the olfactory bulbs and tubercles have been suggested to be large in the kiwi relative to other birds, although the extent of this enlargement is poorly understood. In this study, we examine the size of the olfactory bulbs in kiwi and compare them with 55 other bird species, including emus, ostriches, rheas, tinamous, and 2 extinct species of moa (Dinornithiformes). We also examine the cytoarchitecture of the olfactory bulbs and olfactory epithelium to determine if any neural specializations beyond size are present that would increase olfactory acuity. Kiwi were a clear outlier in our analysis, with olfactory bulbs that are proportionately larger than those of any other bird in this study. Emus, close relatives of the kiwi, also had a relative enlargement of the olfactory bulbs, possibly supporting a phylogenetic link to well-developed olfaction. The olfactory bulbs in kiwi are almost in direct contact with the olfactory epithelium, which is indeed well developed and complex, with olfactory receptor cells occupying a large percentage of the epithelium. The anatomy of the kiwi olfactory system supports an enhancement for olfactory sensitivities, which is undoubtedly associated with their unique nocturnal niche.

3.0 Tesla magnetic resonance imaging anatomy of the central nervous system, eye, and inner ear in birds of prey

“…In the present study, the olfactory bulbs were consistently T2‐weighted hyperintense to the remaining brain parenchyma; this feature was not reported in previous studies describing the MRI anatomy of the avian brain . The cause of different signal behavior is unknown; one possible explanation is the laminar organization of the olfactory bulb, in contrast to the nuclear organization of the remaining parts of the telencephalon …”

Kiwi genome provides insights into evolution of a nocturnal lifestyle

“…Kiwi are unique among birds in having nostrils present at the end of their prominent beaks and have been reported to depend largely on tactile and olfactory senses for foraging [ 39 ]. To investigate whether the genome shows signs of olfactory adaptation in kiwi we assessed the numbers of olfactory receptor (OR) genes [ 40 ] and the diversity in the OR sequence [ 41 ].…”

Zebrin II Expression in the Cerebellum of a Paleognathous Bird, the Chilean Tinamou <b><i>(Nothoprocta perdicaria)</i></b>

“…The ratites are, for the most part, a highly derived group relative to their paleognathous ancestors and tinamous [Feduccia, 1999]. For example, kiwi (Apteryx mantelli) have evolved a number of unique sensory adaptations to function in a nocturnal ground-dwelling niche [Corfield et al, 2011[Corfield et al, , 2014aCunningham et al, 2013;Martin et al, 2007]. Similarly, the other ratites differ markedly in their anatomy and ecology from tinamous and neognathous birds [Davies, 2002].…”