Background Information

This is the first record of a Razorbill (Alca torda) being discovered in the stomach contents of a Snowy Owl (Bubo scandiacus). The Razorbill is a large, diving seabird of the northern Atlantic Ocean, however they can migrate as far south as New Jersey (Cornell, 2015). This falls within the Snowy Owl’s range, since they also live in the arctic and can migrate as far south as Texas and Florida. Snowy Owls are known to feed on rodents, rabbits, ducks, and various seabirds like grebes (Cornell, 2015). Optimizing search strategy by predators for prey items increases foraging efficiency in a changing environment, thus it strongly impacts their movement patterns (Shoji et al, 2016). Note, the irruptive migration of snowy owls correlates with the breeding success hypothesis, where high abundance of food during the summer permits for high production of young, and thus increases the number of snowy owls migrating south the next winter (Robillard et al, 2016). There were abnormally intense irruptions of Snowy Owls along the eastern North American provinces, states, and the Great Lakes region, for the winters of 2013-2014 and 2014-2015 (Therrien et al, 2017).

In this study, Dove and Coddington stated that a Snowy Owl carcass was found at John F. Kennedy International Airport in New York on February 3, 2013. During the autopsy, the stomach contents revealed were feathers, avian bones, a small mammal skull and hair. Comparative bone analysis, morphological comparisons, and geographical data of possible prey availability contributed to determining the species. These methods were necessary because DNA sequences were too degraded in the stomach contents to be valid (Dove and Coddington, 2015).

 

 

Methods

            The bones and feathers from the Snowy Owl’s stomach were cleaned gently by dipping them in hot, soapy water, and then dried carefully with compressed air. Samples from the downy region of the feathers were observed under a compound light microscope, in order to designate the feathers to an order or family of birds. This was because there were no distinct markings on the black or white feathers left (Dove and Coddington, 2015).

Results

            The microscopic feather characters suggested that the bird consumed was from the family Alcidae, based on barb length, colour patterns, and nodal morphology of the downy barbule. For example, they included short barbules with coloured, slightly expanded nodes that had long spines in the mid-section of the barbule (Dove and Coddington, 2015).

The avian bones consisted of a piece of one scapula (shoulder blade), a fragment of the trabecula lateralis (part of the keel), and one furcula (2 fused clavicles) with missing ends. All relevant species of alcids present during February in New York were examined, including the Common Murre, Thick-billed Murre, Razorbill, Dovekie, and Black Guillemot. However, the Dovekie and Black Guillemot have a much smaller furcula than the unknown sample, so they were removed from the list. Both the Common Murre and the Thick-billed Murre have a different angle of expansion from the center of their furcula and the length of their clavicles, so they too were removed from the list. Thus, the sample furcula had the most similar size and angle of a Razorbill’s furcula (Dove and Coddington, 2015).

Note, the mammal skull and hair that was also found in the Snowy Owl’s stomach contents was determined to belong to a meadow vole, based on skull and dental comparisons of museum examples (Dove and Coddington, 2015).

Discussion

            Snowy Owls do hunt murrelets, puffins, and auklets at nesting colonies, during the breeding season. Yet to find a Razorbill as one of their prey items is unusual, due to the abnormal location of this situation occurring in the Razorbill’s southern-most wintering range (Dove and Coddington, 2015). Interestingly enough, Dove and Coddington did find a report on eBird stating that there was a sighting of a Razorbill 11 miles northwest of JFK Airport on 3 February 2013. Furthermore, Razorbill populations were observed to be larger in 2013 than in previous years, and this may have made them more available to the Snowy Owl as prey items. The extreme southward shift in the Razorbills winter distribution is likely due to the southward expansion of breeding range, prey availability, and climate change (Veit and Manne, 2015). It is not known for certain if this specific Razorbill was a prey item or simply scavenged by the Snowy Owl (Dove and Coddington, 2015).

Conclusion

Dove and Coddington demonstrated in this study the importance of examining all possible types of evidence when researching stomach contents, because it improves dietary analyses. This included forensic techniques of microscopy, bone and morphological analyses, predator and prey relationships, geographical and population data, to deduce the identification of the Razorbill as a prey item of Snowy Owls (Dove and Coddington, 2015).

Bonus Video: The Journey of Baltimore the Snowy Owl

 

 

References

Dove, C.J. and Coddington, C.P. 2015. Forensic techniques identify the first record of snowy owl (Bubo scandiacus) feeding on a razorbill (Alca torda). Wilson Journal of Ornithology, 127(3), pp.503-506. Web. 20 October 2017. http://www.bioone.org/doi/abs/10.1676/14-176.1?journalCode=wils

Razorbill. 2015. All About Birds. Cornell Lab of Ornithology. Web. 20 October 2017. https://www.allaboutbirds.org/guide/Razorbill/lifehistory

Robillard, A., Therrien, J.F., Gauthier, G., Clark, K.M. and Bêty, J., 2016. Pulsed resources at tundra breeding sites affect winter irruptions at temperate latitudes of a top predator, the snowy owl. Oecologia, 181(2), pp.423-433. Web. 9 October 2017. https://link.springer.com/article/10.1007/s00442-016-3588-3

Shoji, A., Aris-Brosou, S., Owen, E., Bolton, M., Boyle, D., Fayet, A., Dean, B., Kirk, H., Freeman, R., Perrins, C. and Guilford, T. 2016. Foraging flexibility and search patterns are unlinked during breeding in a free-ranging seabird. Marine Biology, vol. 163, no. 4, pp. 1-10. Web. 20 October 2017. https://link-springer-com.ezproxy.viu.ca/article/10.1007%2Fs00227-016-2826-x

Therrien, J.F., Weidensaul, S., Brinker, D., Huy, S., Miller, T., Jacobs, E., Weber, D., McDonald, T., Lanzone, M., Smith, N. and Lecomte, N. 2017. Winter Use of a Highly Diverse Suite of Habitats by Irruptive Snowy Owls. Northeastern Naturalist, 24(sp7), pp.B81-B89. Web. 20 October 2017. http://www.bioone.org/doi/abs/10.1656/045.024.s712

Veit, R.R. and Manne, L.L. 2015. Climate and changing winter distribution of alcids in the Northwest Atlantic. Frontiers in Ecology and Evolution, vol. 3. Web. 20 October 2017. https://www.frontiersin.org/articles/10.3389/fevo.2015.00038/full