Examination of the Bill and Buccal Cavity of an Adult Razorbill
(Alca torda) Specimen from the Dry Tortugas, December 18, 2012
During the winter of 2012-2013, hundreds of Razorbills were seen off the coasts of South Florida; an unprecedented event in recorded history. Most of the documented birds that engaged in this ‘invasion’ event appeared to be young or immature. The distinctive bill of the species has received significant attention in several studies, and has been suggested as an aid in determining the maturity of individual birds. Considering the relative few adult individuals documented on Florida waters this winter, the finding of an adult Alca torda corpse in the Dry Tortugas (DRTO) during the Christmas Bird Count (113th) expedition offered a unique opportunity to closely examine a mature bill. The fresh specimen also presented an opportunity to study the uncorrupted interior of the mouth and the buccal organs, which are adapted to catching and retaining fish prey and are bright yellow in adult birds.
The bill of the Alca torda – or Razorbill – is perhaps the most distinctive physical trait of the species. With maturity, the bill may grow to be a relatively large and laterally compressed organ with a steeply curved culmen and a complex sculpting of grooves and ridges. Birds develop an arching white “band” across the upper and lower mandibles as they age, and rarely two bands. The bill undergoes many stresses while foraging and during breeding disputes, and may develop a buttressed sculpt to reinforce the narrow organ. The mouth interior and tongue of adults are an intense warm yellow. These are used in breeding displays and to incite feeding behavior.
By contrast, the bills of younger birds have flatter culmens, and may be entirely devoid of grooves. At all ages, the bill is primarily black and glossy, with a hooked tip and sharp distal tomia that flatten and broaden towards the gape. The interior of the juvenile mouth is pale yellow.
After breeding, Razorbills will shed the outermost layer of the bill, reducing its overall size, and dulling its gloss and color. This shedding of the external sheath of the bill is true also of other alcids, particularly the puffins (Fratercula). With the arrival of the breeding season, an outer keratin layer develops; in the Alcidae this may be manifested in the form of plates, knobs or horny projections that serve as ornamentation for courtship purposes. In Razorbills, the sculpting of the bill’s grooves becomes pronounced, the ridges smoother and rounder, and the black darker and glossier, contrasting a whiter band when present.
Studies at breeding colonies have explored the potential for aging individual Razorbills based on the number and characteristic of bill grooves (Jones 1988). However, the shape and sculpture of bills is variable individually, geographically and possibly even sexually in Razorbills. It is unclear how sexual maturity relates to bill development. Some Razorbills have been known to breed earlier in Nearctic colonies, compared to the Palearctic (Lavers et al. 2008). In general, the bill develops slowly in the species, and may continually become deeper and more grooved in some birds as they age.
The distinctive white band across the bill does not generally begin developing until approximately 15 months of age, so it is unlikely that birds in their first winter show any sign of this trait. Rarely, old birds with two bands have been documented, but this may be associated with geographical tendencies. As Razorbills age and the bill becomes deeper, one proximal groove, and up to three grooves distal of the white band may develop.
The ageing of Razorbills based on the development of their bills cannot be done with accuracy, in part because sexual maturity in the species may be attained anytime between the third and sixth year of life. Some birds may never develop more than a single distal groove their entire lifespan, and this may influence their success as breeders (De Wijs 1983). A 1988 study by Jones demonstrated through the trapping and measuring of breeding birds in the Palearctic that a small margin of birds (9%) had developed a third groove distal of the white band. Only birds past their third summer had more than two distal grooves. That study also showed a tendency for bill depth and wing length to increase with age.
The impromptu situation during this Christmas Bird Count expedition to the Dry Tortugas (December 18-20, 2012) did not allow for the proper measuring of the found corpse, therefore it is hoped that a prepared specimen will supply future details. On the other hand, this might have been one of the only opportunities to examine the remarkable yellow buccal cavity of the bird, since internal tissue deterioration had likely commenced, and frozen birds may present challenges in this camp.
In addition to ornamental bill parts, the Alcidae are also known for colorful mouth interiors, used during threat displays and courtship. These range from light blue in Ancient Murrelet (Synthliboramphus antiquus) to vermilion in guillemots (Cepphus), and are yellow-orange in breeding Razorbills. Additionally, their mouths and tongues are equipped with specialized projections and gripping accessories that allow for the trapping of slippery prey.
During the breeding season, Razorbills may carry multiple fish from several fishing bouts crosswise on their bills. Prey such as capelin or sandlace are carried by breeding adults from the ocean back to nest sites on cliff ledges, and fed to the young. The Razorbill’s buccal organs are well adapted for continually foraging and catching prey while securely retaining earlier catches. After fish are caught, they are slipped back towards the gape with the aid of the smooth anterior end of the tongue. The fish are gripped tightly against the horny palate by projections on the posterior of the tongue. The knobbed and flexible inner lining of the mouth helps secure prey. In this manner, a Razorbill is able to repeatedly open its bill to continue foraging while as many as half a dozen fish remain in place.
Working from the Dead Specimen
I found this freshly deceased Razorbill washed up on the southeastern-most shoreline of Garden Key, in Dry Tortugas National Park on the evening of December 18, the night before the annual Christmas Bird Count. During these occasions, our count team stays in the barracks of Fort Jefferson, which offer modest accommodations but no suitable work space. I spent much of that night awake, sketching this Razorbill under flashlights and my headlamp.
The renderings of the bill and buccal cavity of this specimen were drafted from direct observation, aiming to depict proportionate relationships in the form and shapes of each organ. No calipers were used, nor was there an opportunity to make drawings based on measurements. The specimen was surrendered to the National Park Service and transported back to the mainland in the freezer of the NPS M/V Fort Jefferson vessel. I was informed that it would be taken to a research facility for preparation and possible eventual submission to the Florida Museum of Natural History at UF.
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