Gulls, belonging to the Larus genus, are recognizable seabirds found in coastal and marine environments across the globe. Their successful survival is largely attributed to their opportunistic, generalist feeding habits. While their lives revolve around water, the extent of their time beneath the surface is far more limited than many people assume.
Diving Habits and Maximum Breath-Hold Time
Gulls are not built for prolonged underwater activity, which is reflected in their short breath-hold capacity. The typical submersion time during foraging is only a few seconds, often less than ten. For species that engage in a deeper “plunge dive,” such as the Great Black-backed Gull, the maximum breath-hold time is around 10 to 15 seconds. This brief duration is sufficient for their primary feeding strategy: snatching prey close to the water’s surface.
Their foraging dives are quick, vertical plunges from the air, or simple surface dips, rather than sustained underwater pursuit. The purpose is to seize prey immediately upon impact, using the drop’s momentum to gain a shallow depth. This behavioral constraint means their physiological limits are rarely tested, as they return to the surface almost instantly.
Unique Avian Physiology for Submersion
The avian respiratory system, while highly efficient for flight, is not optimized for deep or long-duration submersion. Bird lungs operate with a unique cross-current exchange mechanism, which allows for effective oxygen extraction from the air. This efficiency helps sustain the high metabolic demands of flight, but does not translate into massive oxygen reserves for extended apnea. The respiratory system also includes a series of air sacs distributed throughout the body.
These air sacs pose a significant limitation underwater because they contribute to high buoyancy. A gull must expend considerable energy to overcome this natural floatation, limiting the depth and duration of any dive. Furthermore, while most diving vertebrates exhibit a strong diving reflex—a sharp drop in heart rate (bradycardia) to conserve oxygen—gulls show a much less pronounced response during their brief dives. In some short dives, a gull’s heart rate may not decrease below resting levels, or may even increase due to the physical exertion of the descent and re-surfacing.
Comparing Gulls to Specialized Diving Birds
The short breath-hold time of a gull is best understood by comparing its anatomy to birds specialized for aquatic hunting. Gulls are classified as “plunge divers,” meaning their body plan is adapted for aerial agility and buoyancy. Their bones are relatively light and porous, which is advantageous for flying but challenges staying submerged.
In contrast, specialized aquatic birds like penguins (wing divers) and cormorants (foot divers) have evolved a denser, heavier body structure. These true pursuit divers possess solid bones and greater muscle mass, helping them counteract buoyancy and remain underwater. Specialized divers use their wings or feet for underwater propulsion, whereas gulls rely solely on the initial momentum of their plunge. Furthermore, the compressed plumage of a cormorant allows it to shed air and reduce buoyancy, an adaptation absent in the flight-centric feather structure of a gull.