Pelicans are among the most recognizable birds in the world, known for their massive bills and expansive throat pouches. As large, iconic seabirds, they are frequently observed gliding over ocean waves or resting along coastal shorelines. This constant presence in marine environments raises a question about their hydration: how does a bird manage to drink without becoming dehydrated? The answer lies in biological adaptations that allow pelicans to process the high sodium content of their environment.
Pelican Habitat and Water Consumption
Pelicans can and do drink salt water, but they primarily minimize this intake by getting moisture from their diet. The fish they consume contain substantial water, which helps meet their daily fluid requirements. Marine species, such as the Brown Pelican, constantly ingest saltwater while fishing, particularly when plunge-diving for prey. This regular intake of sodium-rich fluid means they must have a mechanism to manage the salt load, as freshwater is often inaccessible in their oceanic habitat.
The eight species of pelicans exhibit a range of habitats; some, like the American White Pelican, inhabit inland freshwater lakes and rivers. Even inland birds may encounter brackish or mildly saline waters, and all pelicans can process salt. Avian kidneys cannot produce urine saltier than seawater, meaning a bird drinking ocean water would lose more water than it gained through normal excretion. This physiological limitation necessitates a specialized system to maintain the body’s internal water balance.
Specialized Salt Glands for Desalination
Pelicans possess a sophisticated adaptation called the supraorbital salt gland, which acts as a secondary excretory system for sodium. These paired glands are positioned in bony depressions above the bird’s eyes (orbits). They are densely supplied with blood vessels that filter excess salt directly from the bloodstream before it overwhelms the kidneys. The gland is more efficient than the kidney at concentrating and eliminating sodium chloride.
The process involves the active transport of salt ions from the blood into the gland’s tubules, where the sodium is concentrated into a hypertonic solution, or brine. This concentrated liquid can contain a salt content that is up to five times higher than that of the ingested seawater. The fluid travels through ducts and is excreted through the bird’s nostrils (nares), which are located on the upper part of the bill. The salty liquid often drips from the tip of the beak or is expelled with a shake of the head. This extrarenal excretion system ensures that the pelican can achieve a net gain of fresh water from its intake.
Water Conservation and Freshwater Seeking Behavior
Although the salt glands are highly effective, pelicans prefer to use them as a last resort and seek out freshwater when possible. They often take advantage of rainstorms, tilting their heads back to collect the fresh water in their large pouches. Pelicans also congregate near river mouths, freshwater runoff, or temporary pools near the coast to drink, allowing the salt glands to remain dormant or minimally active. This behavioral preference shows that using naturally fresh sources conserves energy.
Pelicans also employ behavioral and anatomical strategies to reduce water loss in warm environments. They dissipate excess heat through gular fluttering, which involves vibrating the skin of their throat pouch for evaporative cooling. Minimizing strenuous activity during the hottest parts of the day further conserves water obtained from food and the environment. Survival is a combination of obtaining moisture through prey, seeking freshwater sources, and relying on specialized salt glands when necessary.