Rhinoceros Auklet vs Cassin's Auklet

In short

The Rhinoceros Auklet is distinguished by its prominent rhinoceros-like 'horn' on the upper mandible during breeding season, while Cassin's Auklet lacks this feature entirely. Both species are medium-sized auks, but differ in behavior and habitat preferences.

Identification tips

• Look for the 'horn' on the bill of the Rhinoceros Auklet during breeding season.
• Note the larger size and more robust build of the Rhinoceros Auklet compared to Cassin's Auklet.
• Observe behavior: Rhinoceros Auklet carries fish externally, while Cassin's Auklet does not.
• Consider habitat: Rhinoceros Auklet is often closer to shore, Cassin's Auklet is more pelagic.

Size

Both species are medium-sized auks, but the Rhinoceros Auklet is generally larger and more robust than Cassin's Auklet.

Plumage

Rhinoceros Auklet has a grayish body with a distinctive 'horn' on the bill during breeding, while Cassin's Auklet is uniformly gray without any bill ornamentation.

Behaviour

Rhinoceros Auklet is primarily nocturnal at breeding colonies and carries fish externally. Cassin's Auklet is also nocturnal but does not have the same fish-carrying behavior.

Habitat

Rhinoceros Auklet is found in temperate North Pacific waters, often closer to shore during breeding. Cassin's Auklet prefers offshore waters and is more pelagic.