Figure 1: Images of a Chukar Partridge and a Pheasant 1,2
With nearly 11,000 species of living birds comprising a vast spectrum of shapes, colors, and sizes, there are immense challenges to fully quantify and analyze avian phenotypic disparity. From a functional perspective, there are several weight-saving adaptations that are reflected in bone shape, many of which strengthen and stiffen the skeleton. As bone density increases, so do bone stiffness and strength. Studies demonstrate that bone shape and the material properties of bone tissue are important in understanding the evolution of flight. Other insights reveal how bird skeletons appear to be thin and delicate but contribute just as much to total body mass as do the skeletons of terrestrial mammals.
In addition to morphological characterization, other research has focused on evolutionary change in the shape of that most ecologically adaptable avian feature, the beak. Avian beaks are made of structural biocomposite materials with an exterior of keratin and a fibrous bony network of closed cells made of trabeculae. The bony foam core or trabecular bone is a closed-cell foam, which serves as a stiffener and lightweight framework for the beak.
Micro-CT’s non-destructive, high resolution 3D imaging makes it one of the most important tools for morphological avian research as well as biomimetic studies.
X-Ray Microscopy Imaging of Avian Skulls
To compare skulls from two similar game birds, a Chukar Partridge and a Hen Pheasant skull were both imaged using the SkyScan 1275 high-speed desktop micro-CT. Samples were collected from specimens obtained during a hunting trip and were stored in a freezer until imaging. For imaging, the samples were scanned in their frozen state without further defrosting.
Figure 2: Planar 2D views through the Chukar Partridge skull
In inspecting the results from the Chukar Partridge, DataViewer provides us a live linked planar view through the three orientations of the sample (Figure 2). From the image, we observe the fine details captured relating to the cortical and trabecular bone present within the skull derived from the 35µm isotropic voxel size used in acquiring the data.
Figure 3: Rendered 3D MIP view of a Chukar Partridge skull
Likewise, we obtain a broader overview image of the sample using CTVox to produce a maximum intensity projection (MIP) image of the Chukar Partridge skull (Figure 3). Within the sample, the greatest density is present in the beak of the Chukar Partridge, as shown by the enhanced brightness in this region within this MIP image.
Figure 4: Planar 2D views through the Hen Pheasant skull
In inspecting the results from the Hen Pheasant, DataViewer once again shows the fine bone morphometric details in the larger sample (Figure 4).
Figure 6: Rendered 3D MIP view of a Hen Pheasant skull
Inspecting the MIP image from the Hen Pheasant skull, the details in the orbital sockets of the skull are prominently displayed (Figure 6). Similar to the Chukar Partridge, the highest density region is once again the beak.
Conclusion
The SkyScan 1275 allowed us to easily examine skulls from two similar game birds with image acquisition times of about an hour. While keeping the acquisition times short, the fine details present in the cortical and trabecular bone are still evident for both samples. We hope you found this Image of the Month informative and encourage you to subscribe to our newsletter and social media channels in preparation for the continuation of our image of the month series next month.
Scan Specifications
| Sample | Avian Skulls |
| Voltage (kV) | 40 |
| Current (µA) | 90 |
| Pixel Size (µm) | 35 |
| Rotation Step | 0.4 |
| Scan Time (HH:MM:SS) | 01:06:18 |
These scans were completed on our desktop SkyScan 1275 system at the Micro Photonics Imaging Laboratory in Allentown, PA. Reconstructions were completed using NRecon 2.1 and visualization of 2D and 3D results were completed using DataViewer and CTVox.
Would you like your work to be featured in our monthly newsletter? If so, please contact us by calling Seth Hogg at 610-366-7103 or e-mailing seth.hogg@microphotonics.com.
References