The razorbill is a medium-sized seabird that is part of the auk family. Understanding the typical size of a razorbill can provide insight into their lifestyle, habitat, and more. In this article, we will explore the various measurements of razorbill size to get a comprehensive understanding of how large this seabird truly is.
Overall Size
The razorbill has a stout body shape that is well adapted for diving and swimming. From head to tail, the average length of a razorbill is about 18 inches (45 cm). Their wingspan ranges from 24-29 inches (61-74 cm). Overall, they are about the size of a pigeon.
Some key size measurements for an average adult razorbill include:
- Length: 16-19 inches (40-48 cm)
- Wingspan: 24-29 inches (61-74 cm)
- Weight: 1.5-2.2 pounds (680-1000 grams)
Compared to other auk species, the razorbill is on the larger end of the size spectrum. Their heavier weight and robust build allows them to dive deeper than other auks when searching for food beneath the ocean’s surface.
Head and Beak
Like other auks, the razorbill has a distinctive narrow, pointed beak that is longer than it is deep. Their beak averages about 1 inch (2.5 cm) in length.
During breeding season, the beak takes on a white and black striped pattern. The rest of the year it is solid black. Their black beak is adapted for grasping slippery fish and crustaceans.
The head of a razorbill is rounded at the crown. Their face has a puffin-like appearance with a short thick neck and piercing yellow eyes. Razorbills have sleek black feathers on the top of their head that transition into white feathers on the cheeks and chin.
Body and Plumage
Razorbills have compact, plump bodies that are well-insulated with waterproof feathers. Their dense feathering helps conserve heat while swimming in frigid northern waters.
During breeding season, razorbill plumage is entirely black on the head, back, and flippers. Their underparts are white. The white belly contrasts sharply with the black back and reduces countershading, making them less visible to predators looking up at them from below the water’s surface.
In winter, their throat and sides of the neck become white like the belly, creating a black hood appearance. The winter plumage is similar between males and females.
Juvenile razorbills have more brownish plumage compared to the black adults. After 2-3 years they molt into adult feathers.
Wings
The wings of the razorbill are relatively narrow. This helps propel them underwater when pursuing prey. Their wingspan ranges from 24-29 inches (61-74 cm).
In flight, they beat their wings rapidly to compensate for their short wing area and heavy body weight. Razorbills can reach flight speeds up to 60 mph during migration.
Their wings are adapted for both flying and underwater swimming. The wings provide powerful thrust underwater while steering with the feet and tail.
Legs and Feet
A razorbill’s legs are set far back on its body, providing them with excellent swimming capability but making them awkward on land. Their feet have leathery webbing for paddling underwater.
On average, a razorbill’s legs measure about 2 inches (5 cm) long from the tarsal joint to the end of the toes. Their outer toe is the longest, measuring around 2 inches (5 cm). The inner toe is slightly smaller at 1.5 inches (4 cm). The arrangement of three toes pointing forward and one pointing back provides excellent maneuverability while swimming.
Razorbill’s feet and webbed toes propel them gracefully through the water in pursuit of fish. They can flap their wings underwater to gain speed when chasing prey.
Weight
The thickset body and dense plumage of the razorbill gives them substantial weight for their body size. Adults weigh from 1.5-2.2 pounds (680-1,000 grams), with males tending to be slightly heavier than females.
Some key weight figures include:
- Male Weight: 1.7-2.2 pounds (770-1,000 grams)
- Female Weight: 1.5-2 pounds (680-900 grams)
The higher weight compared to related auk species allows razorbills to dive to greater depths, sometimes up to 120 m when searching for fish and crustaceans.
Size Comparisons
Comparing the razorbill’s size to other familiar birds can provide a better understanding of their overall stature:
- About 1/3 larger than a pigeon
- Over 3 times larger than a blue jay
- About 2/3 the size of a mallard duck
- Less than 1/2 the size of a common murre
Some examples of birds that are similar in size to the razorbill include:
- Cassin’s Auklet
- Rhinoceros Auklet
- Long-tailed Duck
Overall, the medium size, heavy build, and adapted wings of the razorbill allow it chase down agile fish and withstand the pressure of deep dives into cold northern waters. Their specialized body contributes to their prowess as underwater hunters.
Male vs Female Size
Male and female razorbills are similar in size, with males averaging slightly larger in weight. However, the size difference between genders is minor.
During courtship displays, the male and female razorbill appear nearly identical in size as they swim together. Within a breeding pair, the male may exceed the female in weight by just a few ounces.
Key size differences between genders include:
- Males typically weigh 1.7-2.2 lbs compared to 1.5-2 lbs in females
- Male wingspan around 1-2 inches longer than females
- Male bills tend to be very slightly longer and deeper
- Females may have slightly shorter tails
The small disparity in weight allows males to dive marginally deeper than females when hunting prey. However, during incubation shifts the female must rely solely on her fat reserves, so she is under evolutionary pressure to maintain a similar healthy body size and weight as males.
Juvenile vs Adult Size
Juvenile razorbills are distinctly smaller than adult birds. They reach about 2/3 of adult body size in their first year.
Some key size differences between juveniles and adult razorbills include:
- Juvenile Length: 14 inches vs 18 inches in adults
- Juvenile Wingspan: 20 inches vs 24-29 inches in adults
- Juvenile Weight: 1 – 1.25 lbs vs 1.5-2.2 lbs in adults
The smaller body size of juveniles likely makes them more vulnerable to predation. Their wings also are not fully developed, so they cannot dive as deep or fly as powerfully as adults. Juvenile feathers provide camouflage with brownish mottled plumage.
After fledging, juveniles must rapidly gain weight and improve diving capability. They molt into adult plumage after 2-3 years.
Population Size Differences
Interestingly, there are some subtle size differences between razorbill populations depending on their geographic location.
In general, razorbills breeding in more southern areas tend to be slightly larger than those in northern areas. For example, birds in colonies along Maine and eastern Canada average smaller in body size compared to those nesting off Iceland or Norway.
Scientists theorize several factors may contribute to this size discrepancy between populations:
- Colder ocean temperatures in the far north may limit food supply
- More prolonged periods of food scarcity in northern areas
- Genetic differences between populations
- Possibly larger birds are better able to withstand migration from farther north
The size differences are relatively small, but still noticeable in average wingspan and weight. Further research is needed to understand the precise factors driving size variations between breeding colonies.
Evolution of Razorbill Size
The razorbill belongs to the Alcaidae family, which includes the murres and other auks. Evolutionary pressures shaped the razorbill into its distinct size and form to fill its ecological niche.
Some key evolutionary factors that contributed to the razorbill’s size include:
- Shorter wings provide underwater propulsion when pursuing fish
- Dense, waterproof plumage insulates them from frigid waters
- Heavier body weight allows them to dive deeper than other auks
- Compact form reduces drag while swimming
- Large feet and legs adapted for swimming and paddling
Compared to its closest living relative, the common murre, razorbills evolved a smaller overall size but a stockier build and greater weight to fill its niche diving for fish and other prey.
Future changes in ocean temperatures, currents and food chains may exert new evolutionary pressures. The razorbill’s ability to adapt its body size and features will determine its long-term survival.
Conclusion
In summary, the razorbill is a medium-sized seabird with a thickset body profile distinct among the auk family. Adults range from 16-19 inches long with a 24-29 inch wingspan and weigh 1.5-2.2 pounds. Their compact shape, strong wings and heavy weight allow them to pursuit prey underwater. Males tend to be slightly larger than females. Juveniles are noticeably smaller with different coloration. Geographic populations show subtle size variations. The razorbill’s distinctive size and proportions reflect evolutionary adaptations for its role as a seabird that feeds by pursuit diving in northern waters.
