Cormorants are birds recognized for their ability to navigate and hunt beneath the water’s surface. These aquatic specialists spend a significant portion of their lives diving, emerging to dry their distinctive, less-waterproof plumage. Understanding how long these birds can remain submerged reveals much about their biological design and the various influences on their underwater activities.
Typical Dive Duration
Cormorants exhibit a range of dive durations. While some species, such as the blue-eyed cormorant, have been recorded holding their breath for up to 6 minutes and 20 seconds, their everyday foraging dives are often considerably shorter. For instance, the double-crested cormorant commonly dives for about 30 to 70 seconds. Across most cormorant species, the average dive period usually falls within the 20 to 40-second range, though this can extend from 6 to 68 seconds depending on the specific conditions and species. These birds often perform many shorter dives throughout the day, sometimes spending a total of 60 to 100 minutes submerged during their foraging trips.
Remarkable Adaptations for Underwater Living
Cormorants possess several biological features that enable their impressive underwater capabilities. Their bones are denser compared to most other birds, which helps reduce buoyancy and makes submerging easier. Unlike many waterbirds, cormorant feathers are not fully waterproof, allowing them to become saturated with water. This waterlogging decreases the amount of air trapped in their plumage, further reducing their natural buoyancy and aiding their descent into the water column.
Once submerged, a suite of physiological responses, collectively known as the diving reflex, takes over. This reflex involves a significant slowing of the heart rate, called bradycardia. Peripheral vasoconstriction redirects blood flow from less oxygen-sensitive areas, prioritizing delivery to the brain and heart. Cormorants also store oxygen in their powerful leg muscles, crucial for propulsion. These adaptations conserve oxygen stores, allowing birds to maintain aerobic metabolism longer underwater.
Factors Influencing Dive Time
The duration a cormorant spends underwater varies due to environmental and behavioral factors. Prey availability and type play a substantial role; dives for schooling fish near the surface are shorter. Hunting motile prey, requiring active pursuit, is more energetically demanding than capturing stationary food sources.
Water depth also influences dive time. Many cormorant dives occur in shallower waters, typically within 10 meters, but some species reach depths of 45 meters or up to 145 meters in blue-eyed cormorant populations. Deeper dives require more energy and can increase thermoregulatory costs, limiting how long a bird can stay submerged. Water temperature also impacts dive capacity, as colder water elevates their metabolic rate during dives, affecting their underwater endurance. The bird’s energy levels and the efficiency of a foraging area also influence dive duration, as cormorants may minimize time in water if prey is abundant, especially during colder seasons.