Pygmy sperm whales reach a length of at least 11 feet (3.4 m). They are characterized by 1) an extremely robust body that rapidly tapers near the tail, 2) a squarish head, and 3) a narrow, underslung lower jaw which is located well behind the tip of the snout. Along the side of the head, in approximately the same position where gill slits would be located on a fish of comparable size, there is a crescent-shaped bracket mark, often called a false gill.
The flippers, which are smoothly curved on the forward margin and may reach a length of 18 inches (45.7 cm) or more on an adult specimen, are located well forward on the body, just below and behind the bracket mark.
The dorsal fin is very small, falcate, and located in the latter half of the back.
Though coloration can be described only from stranded specimens and a few encounters with living animals, pygmy sperm whales appear to be dark steel gray on the back, shading to a lighter gray on the sides, and gradually fading to a dull white on the belly. The outer surface of the flippers and the upper surface of the tail flukes are also steel gray.
Natural History Notes
From the few accounts, the following may be summarized about the behavior of pygmy sperm whales at sea: They reportedly usually rise slowly to the surface to breathe, produce a blow that is inconspicuous, and do not normally roll aggressively at the surface like most other species of small whales. They reportedly fold their flippers flat against their bodies when swimming. They have been reported to lie motionless in the water with the back of the head on the surface and the tail hanging loosely down in the water. (A similar behavior in sperm whales has made them a minor hazard to shipping, since it has resulted in some collisions with ships.) When they are startled in this posture, they may defecate, issuing a cloud of reddish brown to rust-colored fece. Beached pygmy sperm whales have also been observed to defecate a fine chocolate feces.
Pygmy sperm whales apparently feed primarily on squid, but do take fish as well.
May Be Confused With
In general, when they can be examined at close range, pygmy sperm whales are so distinctive that they are unlikely to be confused with any other species except perhaps the dwarf sperm whales. At a distance, they might be confused with small individuals of any of the beaked-whale species (p. [78]) that also have a relatively small, falcate dorsal fin located in the latter third of the back. Closer examination should permit easy separation, however, since the pygmy sperm whale has a blunted head, while the beaked whales, as the name implies, have elongated "dolphinlike" beaks and are considerably larger. At sea, pygmy sperm whales are most likely to be confused with their cousins the dwarf sperm whales (p. [148] and Fig. [160]). The two species can be distinguished as follows:
| Pygmy Sperm Whale | Dwarf Sperm Whale |
|---|---|
| MAXIMUM SIZE | |
| To 11 feet (3.4 m). | To 9 feet (2.7 m). |
| DORSAL FIN | |
| Small to 8 inches (20.3 cm),falcate; located in latter thirdof back. | Taller, more like that ofbottlenosed dolphins; locatednear the midpoint of theback. |
| COLORATION | |
| Both species are dark steel gray on the back, grading tolighter on the belly. | |