Baleen whales (Mysticetes) are large marine mammals distinguished by their feeding apparatus—baleen plates used to filter small prey from the water. This group includes the largest animals on Earth, such as the blue whale and the humpback whale, which must surface regularly to breathe air. All species of baleen whales possess two blowholes, which are their equivalent of nostrils, located on the top of the head. This double opening is a distinctive physical trait that separates them from the other major group of whales.
The Definitive Answer: Two Blowholes
Baleen whales are defined by having a pair of external openings that function as their airway, positioned far back on the dorsal surface of the head. These two blowholes are separated by a prominent ridge of tissue, which gives the structure a characteristic V-shape when viewed from above in many species, such as the gray whale. The position on the top of the skull evolved to allow the whale to take a breath by exposing only a small portion of its body at the water’s surface. This placement minimizes the energy required for breathing and permits the rest of the massive body to remain submerged.
Each of these two openings is a distinct external naris, or nostril, leading to a separate nasal passage within the whale’s head. The symmetrical nature of these passages is considered a retention of the ancestral condition found in terrestrial mammals. Strong, specialized muscles surround each opening, which are necessary for the whale to actively control the airway. When the whale is submerged, a fibrous plug or flap covers the openings, creating a watertight seal to prevent any water from entering the respiratory tract.
The size and shape of the blowholes can vary slightly among the different families of baleen whales, contributing to the unique appearance of their exhaled breath. For instance, the two slits are more distinct in rorquals, like the fin whale, while the V-shape is particularly pronounced in right whales.
Structural Differences Between Whale Types
The presence of two blowholes is the defining anatomical difference between Mysticetes and Odontocetes, the two infraorders of cetaceans. Toothed whales, including dolphins, porpoises, and sperm whales, possess only a single blowhole opening. This distinction reflects a significant divergence in the evolutionary history of these two groups.
The single blowhole in toothed whales resulted from a dramatic shift in the nasal passages, which fused and migrated to the top of the head in a process known as telescoping of the skull. This evolutionary modification in Odontocetes is intrinsically linked to the development of their sophisticated echolocation system. The second nasal passage in toothed whales became specialized for sound production, contributing to their ability to navigate and hunt using biological sonar.
In contrast, the paired blowholes of the baleen whales represent a more primitive or ancestral mammalian condition, retaining the separation of the nasal passages. This structure suggests that the Mysticete lineage did not undergo the same degree of nasal passage fusion or specialization for sound production as their toothed counterparts. The retention of the separate passages allows baleen whales to maintain a more pronounced sense of smell compared to toothed whales, which may assist in locating large aggregations of prey.
Respiration Mechanics in Baleen Whales
The act of breathing for a baleen whale is a rapid and forceful process that relies on the precise function of the paired blowholes. When the whale breaks the surface, it first performs an explosive exhalation, often referred to as the “blow” or “spout,” which clears the old air from the lungs. This expelled breath contains warm, moist air that condenses upon contact with the cooler atmosphere, creating the visible cloud of mist.
The exhalation is immediately followed by a rapid inhalation of fresh air, a process that can take just one or two seconds in large rorquals. Whales are highly efficient breathers, capable of exchanging up to 90% of the air in their lungs with each breath, far surpassing the efficiency of human respiration.
Because the blowholes are open only for this brief moment, the whale must consciously contract the muscles to open the airway. The quick exchange of air is facilitated by the direct, unobstructed pathway from the two external openings to the lungs. This conscious control is a neurological adaptation that prevents the whale from inadvertently inhaling water while submerged or resting. Once the intake of air is complete, the powerful muscles relax, allowing the fibrous plugs to reseal the nasal passages and protect the respiratory system before the whale descends again.